1.
Dew
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Dew is water in the form of droplets that appears on thin, exposed objects in the morning or evening due to condensation. As the exposed surface cools by radiating its heat, atmospheric moisture condenses at a greater than that at which it can evaporate. When temperatures are low enough, dew takes the form of ice, Dew should not be confused with guttation, which is the process by which plants release excess water from the tips of their leaves. Water vapor will condense into droplets depending on the temperature, the temperature at which droplets form is called the dew point. When surface temperature drops, eventually reaching the dew point, atmospheric water vapor condenses to form small droplets on the surface and this process distinguishes dew from those hydrometeors, which form directly in air that has cooled to its dew point, such as fog or clouds. The thermodynamic principles of formation, however, are the same, Dew is usually formed at night. Adequate cooling of the surface typically takes place when it more energy by infrared radiation than it receives as solar radiation from the sun. Poor thermal conductivity restricts the replacement of such losses from deeper ground layers, preferred objects of dew formation are thus poor conducting or well isolated from the ground, and non-metallic, while shiny metal coated surfaces are poor infrared radiators. Preferred weather conditions include the absence of clouds and little water vapor in the atmosphere to minimize greenhouse effects. Typical dew nights are considered calm, because the wind transports warmer air from higher levels to the cold surface. However, if the atmosphere is the source of moisture. The highest optimum wind speeds could be found on arid islands, if the wet soil beneath is the major source of vapor, however, wind always seems adverse. The processes of dew formation do not restrict its occurrence to the night and they are also working when eyeglasses get steamy in a warm, wet room or in industrial processes. However, the term condensation is preferred in these cases, a classical device for dew measurement is the drosometer. A small, artificial condenser surface is suspended from an arm attached to a pointer or a pen that records the changes of the condenser on a drum. Besides being very sensitive, however, this, like all artificial surface devices. The actual amount of dew in a place is strongly dependent on surface properties. Further methods include estimation by means of comparing the droplets to standardized photographs, some of these methods include guttation, while others only measure dewfall and/or distillation
2.
Plant cuticle
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A plant cuticle is a protecting film covering the epidermis of leaves, young shoots and other aerial plant organs without periderm. It consists of lipid and hydrocarbon polymers impregnated with wax, and is synthesized exclusively by the epidermal cells, the plant cuticle is a layer of lipid polymer impregnated with waxes that is present on the outer surfaces of the primary organs of all vascular land plants. The cuticle is composed of an insoluble cuticular membrane impregnated by, cutin, a polyester polymer composed of inter-esterified omega hydroxy acids which are cross-linked by ester and epoxide bonds, is the best-known structural component of the cuticular membrane. The cuticle can also contain a non-saponifiable hydrocarbon polymer known as Cutan, aerial organs of many plants, such as the leaves of the sacred lotus have ultra-hydrophobic and self-cleaning properties that have been described by Barthlott and Neinhuis. The lotus effect has applications in biomimetic technical materials, dehydration protection provided by a maternal cuticle improves offspring fitness in the moss Funaria hygrometrica. and in the sporophytes of all vascular plants. The waxy sheet of cuticle also functions in defense, forming a barrier that resists penetration by virus particles, bacterial cells
3.
Drop (liquid)
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A drop or droplet is a small column of liquid, bounded completely or almost completely by free surfaces. A drop may form when liquid accumulates at the end of a tube or other surface boundary. Drops may also be formed by the condensation of a vapor or by atomization of a mass of liquid. Liquid forms drops because the liquid surface tension. A simple way to form a drop is to allow liquid to flow slowly from the end of a vertical tube of small diameter. The surface tension of the causes the liquid to hang from the tube. When the drop exceeds a size it is no longer stable. The falling liquid is also a drop held together by surface tension, in the pendant drop test, a drop of liquid is suspended from the end of a tube by surface tension. The force due to surface tension is proportional to the length of the boundary between the liquid and the tube, with the proportionality constant usually denoted γ. Since the length of boundary is the circumference of the tube. The limit of this formula, as α goes to 90°, gives the weight of a pendant drop for a liquid with a given surface tension. M g = π d γ This relationship is the basis of a convenient method of measuring surface tension, more sophisticated methods are available to take account of the developing shape of the pendant as the drop grows. These methods are used if the tension is unknown. In medicine, droppers have a diameter, in such a way that 1 millilitre is equivalent to 20 drops. And, for the cases when smaller amounts are necessary, microdroppers are used, the drop adhesion to a solid can be divided to two categories, lateral adhesion and normal adhesion. Normal adhesion is the required to detach a drop from the surface in the normal direction. The measurement of both forms can be done with the Centrifugal Adhesion Balance. The CAB uses a combination of centrifugal and gravitational forces to any ratio of lateral and normal forces
4.
Ultrahydrophobicity
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Ultrahydrophobic surfaces are highly hydrophobic, i. e. extremely difficult to wet. The contact angles of a water droplet exceed 150° and the roll-off angle/contact angle hysteresis is less than 10° and this is also referred to as the lotus effect, after the superhydrophobic leaves of the lotus plant. A droplet impacting on these kind of surfaces can fully rebound like an elastic ball, in 1805, Thomas Young defined the contact angle θ by analyzing the forces acting on a fluid droplet resting on a solid surface surrounded by a gas. Wenzels equation shows that microstructuring a surface amplifies the natural tendency of the surface, a hydrophobic surface becomes more hydrophobic when microstructured – its new contact angle becomes greater than the original. However, a hydrophilic surface becomes more hydrophilic when microstructured – its new contact angle less than the original. Liquid in the Cassie-Baxter state is more mobile than in the Wenzel state and it can be predicted whether the Wenzel or Cassie-Baxter state should exist by calculating the new contact angle with both equations. By a minimization of free energy argument, the relation that predicted the new contact angle is the state most likely to exist. Stated mathematically, for the Cassie-Baxter state to exist, the following inequality must be true, contact angle is a measure of static hydrophobicity, and contact angle hysteresis and slide angle are dynamic measures. Contact angle hysteresis is a phenomenon that characterizes surface heterogeneity, when a pipette injects a liquid onto a solid, the liquid will form some contact angle. As the pipette injects more liquid, the droplet will increase in volume, the angle will increase. The contact angle the droplet had immediately before advancing outward is termed the advancing contact angle, the receding contact angle is now measured by pumping the liquid back out of the droplet. The droplet will decrease in volume, the angle will decrease. The contact angle the droplet had immediately before receding inward is termed the receding contact angle, the difference between advancing and receding contact angles is termed contact angle hysteresis and can be used to characterize surface heterogeneity, roughness, and mobility. Surfaces that are not homogeneous will have domains which impede motion of the contact line, the slide angle is another dynamic measure of hydrophobicity and is measured by depositing a droplet on a surface and tilting the surface until the droplet begins to slide. Liquids in the Cassie-Baxter state generally exhibit lower slide angles and contact angle hysteresis than those in the Wenzel state, a simple model can be used to predict the effectiveness of a manmade micro- or nano-fabricated surface for its conditional state, contact angle and contact angle hysteresis. The main factor of this model is the line density, Λ. The critical contact line density Λc is a function of body and surface forces, otherwise, the droplet will collapse into the wenzel state. To calculate updated advancing and receding contact angles in the cassie-baxter state, bhushan studied the effect of unitary structures of micro and nano roughness, and hierarchical structures
5.
Chemistry
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Chemistry is a branch of physical science that studies the composition, structure, properties and change of matter. Chemistry is sometimes called the science because it bridges other natural sciences, including physics. For the differences between chemistry and physics see comparison of chemistry and physics, the history of chemistry can be traced to alchemy, which had been practiced for several millennia in various parts of the world. The word chemistry comes from alchemy, which referred to a set of practices that encompassed elements of chemistry, metallurgy, philosophy, astrology, astronomy, mysticism. An alchemist was called a chemist in popular speech, and later the suffix -ry was added to this to describe the art of the chemist as chemistry, the modern word alchemy in turn is derived from the Arabic word al-kīmīā. In origin, the term is borrowed from the Greek χημία or χημεία and this may have Egyptian origins since al-kīmīā is derived from the Greek χημία, which is in turn derived from the word Chemi or Kimi, which is the ancient name of Egypt in Egyptian. Alternately, al-kīmīā may derive from χημεία, meaning cast together, in retrospect, the definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science. The term chymistry, in the view of noted scientist Robert Boyle in 1661, in 1837, Jean-Baptiste Dumas considered the word chemistry to refer to the science concerned with the laws and effects of molecular forces. More recently, in 1998, Professor Raymond Chang broadened the definition of chemistry to mean the study of matter, early civilizations, such as the Egyptians Babylonians, Indians amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didnt develop a systematic theory. Greek atomism dates back to 440 BC, arising in works by such as Democritus and Epicurus. In 50 BC, the Roman philosopher Lucretius expanded upon the theory in his book De rerum natura, unlike modern concepts of science, Greek atomism was purely philosophical in nature, with little concern for empirical observations and no concern for chemical experiments. Work, particularly the development of distillation, continued in the early Byzantine period with the most famous practitioner being the 4th century Greek-Egyptian Zosimos of Panopolis. He formulated Boyles law, rejected the four elements and proposed a mechanistic alternative of atoms. Before his work, though, many important discoveries had been made, the Scottish chemist Joseph Black and the Dutchman J. B. English scientist John Dalton proposed the theory of atoms, that all substances are composed of indivisible atoms of matter. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current, british William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen. The inert gases, later called the noble gases were discovered by William Ramsay in collaboration with Lord Rayleigh at the end of the century, thereby filling in the basic structure of the table. Organic chemistry was developed by Justus von Liebig and others, following Friedrich Wöhlers synthesis of urea which proved that organisms were, in theory
6.
Molecule
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A molecule is an electrically neutral group of two or more atoms held together by chemical bonds. Molecules are distinguished from ions by their lack of electrical charge, however, in quantum physics, organic chemistry, and biochemistry, the term molecule is often used less strictly, also being applied to polyatomic ions. In the kinetic theory of gases, the molecule is often used for any gaseous particle regardless of its composition. According to this definition, noble gas atoms are considered molecules as they are in fact monoatomic molecules. A molecule may be homonuclear, that is, it consists of atoms of one element, as with oxygen, or it may be heteronuclear. Atoms and complexes connected by non-covalent interactions, such as hydrogen bonds or ionic bonds, are not considered single molecules. Molecules as components of matter are common in organic substances and they also make up most of the oceans and atmosphere. Also, no typical molecule can be defined for ionic crystals and covalent crystals, the theme of repeated unit-cellular-structure also holds for most condensed phases with metallic bonding, which means that solid metals are also not made of molecules. In glasses, atoms may also be together by chemical bonds with no presence of any definable molecule. The science of molecules is called molecular chemistry or molecular physics, in practice, however, this distinction is vague. In molecular sciences, a molecule consists of a system composed of two or more atoms. Polyatomic ions may sometimes be thought of as electrically charged molecules. The term unstable molecule is used for very reactive species, i. e, according to Merriam-Webster and the Online Etymology Dictionary, the word molecule derives from the Latin moles or small unit of mass. Molecule – extremely minute particle, from French molécule, from New Latin molecula, diminutive of Latin moles mass, a vague meaning at first, the vogue for the word can be traced to the philosophy of Descartes. The definition of the molecule has evolved as knowledge of the structure of molecules has increased, earlier definitions were less precise, defining molecules as the smallest particles of pure chemical substances that still retain their composition and chemical properties. Molecules are held together by covalent bonding or ionic bonding. Several types of non-metal elements exist only as molecules in the environment, for example, hydrogen only exists as hydrogen molecule. A molecule of a compound is made out of two or more elements, a covalent bond is a chemical bond that involves the sharing of electron pairs between atoms
7.
Intermolecular force
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Intermolecular forces are weak relative to intramolecular forces – the forces which hold a molecule together. For example, the covalent bond, involving sharing electron pairs between atoms, is stronger than the forces present between neighboring molecules. Both sets of forces are essential parts of force fields used in molecular mechanics. The investigation of intermolecular forces starts from macroscopic observations which indicate the existence and these observations include non-ideal-gas thermodynamic behavior reflected by virial coefficients, vapor pressure, viscosity, superficial tension, and absorption data. The first reference to the nature of microscopic forces is found in Alexis Clairauts work Theorie de la Figure de la Terre, other scientists who have contributed to the investigation of microscopic forces include, Laplace, Gauss, Maxwell and Boltzmann. The link to microscopic aspects is given by virial coefficients and Lennard-Jones potentials, dipole-dipole interactions are electrostatic interactions between permanent dipoles in molecules. These interactions tend to align the molecules to increase attraction, an example of a dipole-dipole interaction can be seen in hydrogen chloride, the positive end of a polar molecule will attract the negative end of the other molecule and influence its position. Polar molecules have a net attraction between them, examples of polar molecules include hydrogen chloride and chloroform. H δ + − Cl δ − ⋯ H δ + − Cl δ − Often molecules contain dipolar groups and this occurs if there is symmetry within the molecule that causes the dipoles to cancel each other out. This occurs in such as tetrachloromethane and carbon dioxide. The dipole-dipole interaction between two atoms is usually zero, since atoms rarely carry a permanent dipole. Ion-dipole and ion-induced dipole forces are similar to dipole-dipole and induced-dipole interactions but involve ions, ion-dipole and ion-induced dipole forces are stronger than dipole-dipole interactions because the charge of any ion is much greater than the charge of a dipole moment. Ion-dipole bonding is stronger than hydrogen bonding, an ion-dipole force consists of an ion and a polar molecule interacting. They align so that the positive and negative groups are next to one another, an ion-induced dipole force consists of an ion and a non-polar molecule interacting. Like a dipole-induced dipole force, the charge of the ion causes distortion of the cloud on the non-polar molecule. A hydrogen bond is the attraction between the pair of an electronegative atom and a hydrogen atom that is bonded to either nitrogen, oxygen. The hydrogen bond is described as a strong electrostatic dipole-dipole interaction. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides
8.
Water
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Water is a transparent and nearly colorless chemical substance that is the main constituent of Earths streams, lakes, and oceans, and the fluids of most living organisms. Its chemical formula is H2O, meaning that its molecule contains one oxygen, Water strictly refers to the liquid state of that substance, that prevails at standard ambient temperature and pressure, but it often refers also to its solid state or its gaseous state. It also occurs in nature as snow, glaciers, ice packs and icebergs, clouds, fog, dew, aquifers, Water covers 71% of the Earths surface. It is vital for all forms of life. Only 2. 5% of this water is freshwater, and 98. 8% of that water is in ice and groundwater. Less than 0. 3% of all freshwater is in rivers, lakes, and the atmosphere, a greater quantity of water is found in the earths interior. Water on Earth moves continually through the cycle of evaporation and transpiration, condensation, precipitation. Evaporation and transpiration contribute to the precipitation over land, large amounts of water are also chemically combined or adsorbed in hydrated minerals. Safe drinking water is essential to humans and other even though it provides no calories or organic nutrients. There is a correlation between access to safe water and gross domestic product per capita. However, some observers have estimated that by 2025 more than half of the population will be facing water-based vulnerability. A report, issued in November 2009, suggests that by 2030, in developing regions of the world. Water plays an important role in the world economy, approximately 70% of the freshwater used by humans goes to agriculture. Fishing in salt and fresh water bodies is a source of food for many parts of the world. Much of long-distance trade of commodities and manufactured products is transported by boats through seas, rivers, lakes, large quantities of water, ice, and steam are used for cooling and heating, in industry and homes. Water is an excellent solvent for a variety of chemical substances, as such it is widely used in industrial processes. Water is also central to many sports and other forms of entertainment, such as swimming, pleasure boating, boat racing, surfing, sport fishing, Water is a liquid at the temperatures and pressures that are most adequate for life. Specifically, at atmospheric pressure of 1 bar, water is a liquid between the temperatures of 273.15 K and 373.15 K
9.
Hydrophile
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A hydrophile is a molecule or other molecular entity that is attracted to water molecules and tends to be dissolved by water. In contrast, hydrophobes are not attracted to water and may seem to be repelled by it and they are typically charge-polarized and capable of hydrogen bonding. This makes these molecules soluble not only in water but also in polar solvents. Hydrophilic molecules can be contrasted with hydrophobic molecules, in some cases, both hydrophilic and hydrophobic properties occur in a single molecule. An example of these molecules is the lipids that comprise the cell membrane. Another example is soap, which has a head and a hydrophobic tail. Hydrophilic and hydrophobic molecules are known as polar molecules and nonpolar molecules. Some hydrophilic substances do not dissolve and this type of mixture is called a colloid. Hydrophilic substances can seem to attract water out of the air, sugar is also hydrophilic, and like salt is sometimes used to draw water out of foods. Sugar sprinkled on cut fruit will draw out the water through hydrophilia, making the fruit mushy and wet, liquid hydrophilic chemicals complexed with solid chemicals can be used to optimize solubility of hydrophobic chemicals. Hydroxyl groups, found in alcohols, are polar and therefore hydrophilic, the molecule increasingly becomes overall more nonpolar and therefore less soluble in the polar water as the carbon chain becomes longer. Methanol has the shortest carbon chain of all alcohols followed by ethanol, tert-Butyl alcohol, with four carbon atoms, is the only one among its isomers to be miscible with water. Cyclodextrins are used to make pharmaceutical solutions by capturing hydrophobic molecules as guest hosts, because inclusion compounds of cyclodextrins with hydrophobic molecules are able to penetrate body tissues, these can be used to release biologically active compounds under specific conditions. Hydrophilic membrane filtration is used in industries to filter various liquids. These hydrophilic filters are used in the medical, industrial, and biochemical fields to filter such elements as bacteria, viruses, proteins, particulates, drugs, common hydrophilic molecules include colloids, cotton, and cellulose. Unlike other membranes, hydrophilic membranes do not require pre-wetting, they can filter liquids in their dry state, although most are used in low-heat filtration processes, many new hydrophilic membrane fabrics are used to filter hot liquids and fluids. Hydrophilic-lipophilic balance Hydrophobicity scales Super hydrophilicity Ultrahydrophobicity Wetting
10.
Chemical polarity
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In chemistry, polarity is a separation of electric charge leading to a molecule or its chemical groups having an electric dipole or multipole moment. Polar molecules must contain polar bonds due to a difference in electronegativity between the bonded atoms, a polar molecule with two or more polar bonds must have an asymmetric geometry so that the bond dipoles do not cancel each other. Polar molecules interact through dipole–dipole intermolecular forces and hydrogen bonds, Polarity underlies a number of physical properties including surface tension, solubility, and melting and boiling points. Not all atoms attract electrons with the same force, the amount of pull an atom exerts on its electrons is called its electronegativity. Atoms with high electronegativities – such as fluorine, oxygen and nitrogen – exert a pull on electrons than atoms with lower electronegativities. In a bond, this leads to sharing of electrons between the atoms, as electrons will be drawn closer to the atom with the higher electronegativity. Because electrons have a charge, the unequal sharing of electrons within a bond leads to the formation of an electric dipole. Because the amount of charge separated in such dipoles is usually smaller than a charge, they are called partial charges, denoted as δ+. These symbols were introduced by Christopher Kelk Ingold and Edith Hilda Ingold in 1926, the bond dipole moment is calculated by multiplying the amount of charge separated and the distance between the charges. These dipoles within molecules can interact with dipoles in other molecules, Bonds can fall between one of two extremes – being completely nonpolar or completely polar. A completely nonpolar bond occurs when the electronegativities are identical and therefore possess a difference of zero, a completely polar bond is more correctly called an ionic bond, and occurs when the difference between electronegativities is large enough that one atom actually takes an electron from the other. The terms polar and nonpolar are usually applied to covalent bonds, to determine the polarity of a covalent bond using numerical means, the difference between the electronegativity of the atoms is used. Bond polarity is typically divided into three groups that are based on the difference in electronegativity between the two bonded atoms. He estimated that a difference of 1.7 corresponds to 50% ionic character, see also dipole § Molecular dipoles. While the molecules can be described as covalent, nonpolar covalent, or ionic. However, the properties are typical of such molecules. A molecule is composed of one or more chemical bonds between molecular orbitals of different atoms, a polar molecule has a net dipole as a result of the opposing charges from polar bonds arranged asymmetrically. Water is an example of a polar molecule since it has a positive charge on one side
11.
Dissolution (chemistry)
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Solid solutions are the result of dissolution of one solid into another, and occur, e. g. in metal alloys, where their formation is governed and described by the relevant phase diagram. In the case of a crystalline solid dissolving in a liquid, for liquids and gases, the molecules must be able to form non-covalent intermolecular interactions with those of the solvent for a solution to form. Some distinctions can be made between solvation, dissolution, and solubility, gaseous elements and compounds will dissolve in liquids dependent on the interaction of their bonds with the liquid solvent. Gaseous elements and compounds may dissolve in another liquid depending on the compatibility of the chemical and physical bonds in the substance with those of the solvent. Hydrogen bonds play an important role in aqueous dissolution, for ionic compounds, dissolution takes place when the ionic lattice breaks up and the separate ions are then solvated. e. NaCl ⇌ Na+ + Cl− The solubility of salts in water is generally determined by the degree of solvation of the ions by water molecules. Such coordination complexes occur by water donating spare electrons on the atom to the ion. This in turn results in the remaining particle possessing either a net surface charge. The dissolution of minerals such as silicates occurs by several mechanisms which depend on the composition of the mineral. Dissolution rates partially depend on solution pH, adsorbed protons or hydroxides polarize the mineral surface and weaken cation-oxygen bonds, accelerating dissolution. Silicate minerals containing metal cations undergo incongruent dissolution as the cations out of the mineral faster than the silica lattice degrades. Incongruent dissolution results in a layer with different composition than the bulk. The reductive dissolution of a metal oxide can occur when a redox event in solution reduces a cation. Dissolution occurs when the cation is unstable in the solid material. In minerals such as oxides, reduction may be caused by electron transfer from organic molecules or bacteria in anoxic waters or soils. Charge carriers responsible for reductive dissolution may also be introduced by photoexcitation or by electrochemical poising at negative potentials, reductive dissolution is integral to natural geochemical phenomena such as the iron cycle. However, Fe 2 + is unstable in the oxide lattice relative to the solution and is subsequently solvated, reductants causing reductive dissolution include natural electron donors such as ascorbic acid and Fe 2 +. Chelating species such as oxalate accelerate the process by detaching surface-bound Fe 2 +, reductive dissolution is also promoted by light
12.
Micelle
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A micelle or micella is an aggregate of surfactant molecules dispersed in a liquid colloid. A typical micelle in aqueous solution forms an aggregate with the hydrophilic head regions in contact with surrounding solvent and this phase is caused by the packing behavior of single-tail lipids in a bilayer. This type of micelle is known as a normal-phase micelle, inverse micelles have the head groups at the centre with the tails extending out. Micelles are approximately spherical in shape, other phases, including shapes such as ellipsoids, cylinders, and bilayers, are also possible. The shape and size of a micelle are a function of the geometry of its surfactant molecules and solution conditions such as surfactant concentration, temperature, pH. The process of forming micelles is known as micellisation and forms part of the behaviour of many lipids according to their polymorphism. The ability of a solution to act as a detergent has been recognized for centuries. However, it is only at the beginning of the century that the constitution of such solutions was scientifically studied. Pioneering work in area was carried out by James William McBain at the University of Bristol. As early as 1913, he postulated the existence of “colloidal ions” to explain the good conductivity of sodium palmitate solutions. Individual surfactant molecules that are in the system but are not part of a micelle are called monomers, Micelles represent a molecular assembly, in which the individual components are thermodynamically in equilibrium with monomers of the same species in the surrounding medium. In water, the heads of surfactant molecules are always in contact with the solvent. However, the tails of surfactant molecules have less contact with water when they are part of a micelle—this being the basis for the energetic drive for micelle formation. In a micelle, the tails of several surfactant molecules assemble into an oil-like core. By contrast, surfactant monomers are surrounded by water molecules that create a cage or solvation shell connected by hydrogen bonds and this water cage is similar to a clathrate and has an ice-like crystal structure and can be characterized according to the hydrophobic effect. The extent of solubility is determined by the unfavorable entropy contribution due to the ordering of the water structure according to the hydrophobic effect. Micelles composed of ionic surfactants have an attraction to the ions that surround them in solution. Although the closest counterions partially mask a charged micelle, the effects of micelle charge affect the structure of the surrounding solvent at appreciable distances from the micelle, ionic micelles influence many properties of the mixture, including its electrical conductivity
13.
Contact angle
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The contact angle is the angle, conventionally measured through the liquid, where a liquid–vapor interface meets a solid surface. It quantifies the wettability of a surface by a liquid via the Young equation. A given system of solid, liquid, and vapor at a temperature and pressure has a unique equilibrium contact angle. However, in practice contact angle hysteresis is observed, ranging from the advancing contact angle to the receding contact angle. The equilibrium contact is within those values, and can be calculated from them, the equilibrium contact angle reflects the relative strength of the liquid, solid, and vapor molecular interaction. The shape of an interface is determined by the Young–Laplace equation. The theoretical description of contact arises from the consideration of an equilibrium between the three phases, the liquid phase, the solid phase, and the gas or vapor phase. If we add a small amount of liquid to a drop, the contact line will still be pinned. Similarly, if we remove a small amount of liquid from a drop, the contact line will still be pinned. Hence, a drop placed on a surface has a spectrum of contact angles ranging from the advancing contact angle, θ A, to the so-called receding contact angle. The Young equilibrium contact angle is somewhere between those values, and the contact angle hysteresis is normally defined as θ A − θ R, the Young equation assumes a perfectly flat surface. Even in such a surface a drop will assume contact angle hysteresis. According to the Young–Dupré equation, this means that the adhesion energy varies locally – thus, one consequence of these barriers is contact angle hysteresis, the extent of wetting, and therefore the observed contact angle, depend on whether the liquid is advancing or receding on the surface. Such alterations, if slow, can also produce measurably time-dependent contact angles, for liquid moving quickly over a surface, the contact angle can be altered from its value at rest. The advancing contact angle will increase speed, and the receding contact angle will decrease. The Young–Laplace equation for a drop is highly non-linear. The shapes of three-dimensional sessile and pendant drops have been predicted using this energy minimisation method. If the liquid molecules are attracted to the solid molecules then the liquid drop will completely spread out on the solid surface
14.
Alkane
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In organic chemistry, an alkane, or paraffin, is an acyclic saturated hydrocarbon. In other words, an alkane consists of hydrogen and carbon atoms arranged in a structure in which all the carbon-carbon bonds are single. Alkanes have the chemical formula CnH2n+2. The alkanes range in complexity from the simplest case of methane, CH4 where n =1, in an alkane, each carbon atom has 4 bonds, and each hydrogen atom is joined to one of the carbon atoms. The longest series of linked carbon atoms in a molecule is known as its skeleton or carbon backbone. The number of atoms may be thought of as the size of the alkane. One group of the alkanes are waxes, solids at standard ambient temperature and pressure. They can be viewed as molecular trees upon which can be hung the more functional groups of biological molecules. The alkanes have two main sources, petroleum and natural gas. Saturated hydrocarbons are hydrocarbons having only single covalent bonds between their carbons, according to the definition by IUPAC, the former two are alkanes, whereas the third group is called cycloalkanes. Saturated hydrocarbons can also combine any of the linear, cyclic and branching structures, the formula is CnH 2n−2k+2. Alkanes are the ones, corresponding to k =0. Alkanes with more than three carbon atoms can be arranged in different ways, forming structural isomers. The simplest isomer of an alkane is the one in which the atoms are arranged in a single chain with no branches. This isomer is called the n-isomer. However the chain of atoms may also be branched at one or more points. The number of possible isomers increases rapidly with the number of carbon atoms, for example, 3-methylhexane and its higher homologues are chiral due to their stereogenic center at carbon atom number 3. In addition to the alkane isomers, the chain of atoms may form one or more loops
15.
Oil
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An oil is any neutral, nonpolar chemical substance that is a viscous liquid at ambient temperatures and is both hydrophobic and lipophilic. Oils have a carbon and hydrogen content and are usually flammable. The general definition of oil includes classes of compounds that may be otherwise unrelated in structure, properties. Oils may be animal, vegetable, or petrochemical in origin and they are used for food, fuel, medical purposes, lubrication, and the manufacture of many types of paints, plastics, and other materials. Specially prepared oils are used in religious ceremonies and rituals as purifying agents. First attested in English 1176, the oil comes from Old French oile, from Latin oleum, which in turn comes from the Greek ἔλαιον, olive oil, oil. The earliest attested forms of the word are the Mycenaean Greek
16.
Fat
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Fat is one of the three main macronutrients, along with carbohydrate and protein. Fats, also known as triglycerides, are esters of three fatty acid chains and the alcohol glycerol, the terms oil, fat, and lipid are often confused. Oil normally refers to a fat with short or unsaturated fatty acid chains that is liquid at room temperature, lipid is the general term, as a lipid is not necessarily a triglyceride. Fats, like lipids, are generally hydrophobic, and are soluble in organic solvents. Fat is an important foodstuff for many forms of life, and they are a necessary part of the diet of most heterotrophs. Some fatty acids that are set free by the digestion of fats are called essential because they cannot be synthesized in the body from simpler constituents, there are two essential fatty acids in human nutrition, alpha-linolenic acid and linoleic acid. Other lipids needed by the body can be synthesized from these, fats and other lipids are broken down in the body by enzymes called lipases produced in the pancreas. Fats and oils are categorized according to the number and bonding of the atoms in the aliphatic chain. Fats that are saturated fats have no double bonds between the carbons in the chain, unsaturated fats have one or more double bonded carbons in the chain. The nomenclature is based on the end of the chain. This end is called the end or the n-end. Thus alpha-linolenic acid is called an omega-3 fatty acid because the 3rd carbon from that end is the first double bonded carbon in the counting from that end. Some oils and fats have double bonds and are therefore called polyunsaturated fats. Unsaturated fats can be divided into cis fats, which are the most common in nature, and trans fats. Unsaturated fats can be altered by reaction with hydrogen effected by a catalyst and this action, called hydrogenation, tends to break all the double bonds and makes a fully saturated fat. However, trans fats are generated during hydrogenation as contaminants created by a side reaction on the catalyst during partial hydrogenation. Saturated fats can stack themselves in a closely packed arrangement, so they can easily and are typically solid at room temperature. For example, animal fats tallow and lard are high in saturated fatty acid content and are solids, olive and linseed oils on the other hand are unsaturated and liquid
17.
Oil spill
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An oil spill is the release of a liquid petroleum hydrocarbon into the environment, especially marine areas, due to human activity, and is a form of pollution. The term is applied to marine oil spills, where oil is released into the ocean or coastal waters. Cleanup and recovery from an oil spill is difficult and depends upon factors, including the type of oil spilled, the temperature of the water. Spills may take weeks, months or even years to clean up, oil spills can have disastrous consequences for society, economically, environmentally, and socially. The quantity of oil spilled during accidents has ranged from a few hundred tons to several hundred thousand tons, but volume is a limited barometer of damage or impact. Oil spills at sea are generally much more damaging than those on land and these can kill seabirds, mammals, shellfish and other organisms they coat. Oil spills on land are more readily containable if an earth dam can be rapidly bulldozed around the spill site before most of the oil escapes. An oil spill represents an immediate fire hazard, the Kuwaiti oil fires produced air pollution that caused respiratory distress. The Deepwater Horizon explosion killed eleven oil rig workers, the fire resulting from the Lac-Mégantic derailment killed 47 and destroyed half of the towns centre. Spilled oil can contaminate drinking water supplies. For example, in 2013 two different oil spills contaminated water supplies for 300,000 in Miri, Malaysia,80,000 people in Coca, in 2000, springs were contaminated by an oil spill in Clark County, Kentucky. Contamination can have an impact on tourism and marine resource extraction industries. For example, the Deepwater Horizon oil spill impacted beach tourism and fishing along the Gulf Coast, in general, sрilled oil can affect animals and plants in twо ways, dirесt from the oil and from the respоnsе or cleаnup process. There is no relationship between the amount of oil in the aquatic environment and the likely impact on biodiversity. A smaller spill at the wrong time/wrong season and in an environment may prove much more harmful than a larger spill at another time of the year in another or even the same environment. Animals who rely on scent to find their babies or mothers cannot due to the scent of the oil. This causes a baby to be rejected and abandoned, leaving the babies to starve, oil can impair a birds ability to fly, preventing it from foraging or escaping from predators. As they preen, birds may ingest the oil coating their feathers, irritating the digestive tract, altering liver function, together with their diminished foraging capacity, this can rapidly result in dehydration and metabolic imbalance
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Silicone
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They are typically heat-resistant and rubber-like, and are used in sealants, adhesives, lubricants, medicine, cooking utensils, and thermal and electrical insulation. Some common forms include silicone oil, silicone grease, silicone rubber, silicone resin, more precisely called polymerized siloxanes or polysiloxanes, silicones consist of an inorganic silicon-oxygen backbone chain with organic side groups attached to the silicon atoms. So, silicones are polymers constructed from inorganic-organic monomers, Silicones have in general the chemical formula n, where R is an organic group such as alkyl groups, or phenyl groups. In some cases, organic side groups can be used to two or more of these -Si-O- backbones together. By varying the -Si-O- chain lengths, side groups, and crosslinking, silicones can be synthesized with a variety of properties. They can vary in consistency from liquid to gel to rubber to hard plastic, the most common siloxane is linear polydimethylsiloxane, a silicone oil. The second largest group of materials is based on silicone resins. F. S. Kipping and Matt Saunders coined the word silicone in 1901 to describe polydiphenylsiloxane by analogy of its formula, Ph2SiO, with the formula of the ketone benzophenone, Ph2CO. Kipping was well aware that polydiphenylsiloxane is polymeric whereas benzophenone is monomeric and noted that Ph2SiO, Silicone is sometimes mistakenly referred to as silicon. The chemical element silicon is a crystalline metalloid widely used in computers, polysiloxanes are among the many substances commonly known as silicones. Molecules containing silicon-oxygen double bonds do exist and are called silanones, despite this, silanones are important as intermediates in gas-phase processes such as chemical vapor deposition in microelectronics production, and in the formation of ceramics by combustion. Most common are materials based on polydimethylsiloxane, which is derived by hydrolysis of dimethyldichlorosilane and this dichloride reacts with water as follows, n Si2Cl2 + n H2O → n + 2n HCl The polymerization typically produces linear chains capped with Si-Cl or Si-OH groups. Under different conditions the polymer is a cyclic, not a chain, for consumer applications such as caulks silyl acetates are used instead of silyl chlorides. The hydrolysis of the produce the less dangerous acetic acid as the reaction product of a much slower curing process. This chemistry is used in consumer applications, such as silicone caulk. Branches or cross-links in the chain can be introduced by using organosilicon precursors with fewer alkyl groups. Ideally, each molecule of such a compound becomes a branch point and this process can be used to produce hard silicone resins. Similarly, precursors with three groups can be used to limit molecular weight, since each such molecule has only one reactive site
19.
Fluorocarbon
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Compounds with the prefix perfluoro- are hydrocarbons, including those with heteroatoms, wherein all C-H bonds have been replaced by C-F bonds. Fluorocarbons and their derivatives are useful fluoropolymers, refrigerants, solvents, perfluoroalkanes are very stable because of the strength of the carbon–fluorine bond, one of the strongest in organic chemistry. Additionally, multiple carbon–fluorine bonds increase the strength and stability of other nearby carbon–fluorine bonds on the same geminal carbon, furthermore, multiple carbon–fluorine bonds also strengthen the skeletal carbon–carbon bonds from the inductive effect. Therefore, saturated fluorocarbons are more chemically and thermally stable than their corresponding hydrocarbon counterparts and they are susceptible to attack by very strong reductants, e. g. Birch reduction and very specialized organometallic complexes. Fluorocarbons are colorless and have high density, up to twice that of water. They are not miscible with most organic solvents, but are miscible with some hydrocarbons and they have very low solubility in water, and water has a very low solubility in them. As the high electronegativity of fluorine reduces the polarizability of the atom, as a result, fluorocarbons have low intermolecular attractive forces and are lipophobic in addition to being hydrophobic and non-polar. Reflecting the weak intermolecular forces these compounds exhibit low viscosities when compared to liquids of similar boiling points, low surface tension, the low attractive forces in fluorocarbon liquids make them compressible and able to dissolve gas relatively well. There are five perfluoroalkane gases, tetrafluoromethane, hexafluoroethane, octafluoropropane, perfluoro-n-butane and perfluoro-iso-butane, nearly all other fluoroalkanes are liquids, the most notable exception is perfluorocyclohexane, which sublimes at 51 °C. Fluorocarbons also have low energies and high dielectric strengths. Perfluoroalkanes In the 1960s there was a lot of interest in fluorocarbons as anesthetics, fluorocarbons have been considered as fire extinguishants to replace CFCs. This extinguishing effect has been attributed to their heat capacity. It has been suggested that an atmosphere containing a significant percentage of perfluorocarbons on a station or similar would prevent fires altogether. When combustion does occur, toxic fumes result, including carbonyl fluoride, carbon monoxide, perfluorocarbons dissolve relatively high volumes of gases. The high solubility of gases is attributed to the weak interactions in these fluorocarbon fluids. This table shows values for the fraction, x1, of nitrogen dissolved, calculated from the Ostwald coefficient. The development of the fluorocarbon industry coincided with World War II, prior to that, fluorocarbons were prepared by reaction of fluorine with the hydrocarbon, i. e. direct fluorination. Because C-C bonds are cleaved by fluorine, direct fluorination mainly affords smaller perfluorocarbons, such as tetrafluoromethane, hexafluoroethane
20.
Ancient Greek
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Ancient Greek includes the forms of Greek used in ancient Greece and the ancient world from around the 9th century BC to the 6th century AD. It is often divided into the Archaic period, Classical period. It is antedated in the second millennium BC by Mycenaean Greek, the language of the Hellenistic phase is known as Koine. Koine is regarded as a historical stage of its own, although in its earliest form it closely resembled Attic Greek. Prior to the Koine period, Greek of the classic and earlier periods included several regional dialects, Ancient Greek was the language of Homer and of fifth-century Athenian historians, playwrights, and philosophers. It has contributed many words to English vocabulary and has been a subject of study in educational institutions of the Western world since the Renaissance. This article primarily contains information about the Epic and Classical phases of the language, Ancient Greek was a pluricentric language, divided into many dialects. The main dialect groups are Attic and Ionic, Aeolic, Arcadocypriot, some dialects are found in standardized literary forms used in literature, while others are attested only in inscriptions. There are also several historical forms, homeric Greek is a literary form of Archaic Greek used in the epic poems, the Iliad and Odyssey, and in later poems by other authors. Homeric Greek had significant differences in grammar and pronunciation from Classical Attic, the origins, early form and development of the Hellenic language family are not well understood because of a lack of contemporaneous evidence. Several theories exist about what Hellenic dialect groups may have existed between the divergence of early Greek-like speech from the common Proto-Indo-European language and the Classical period and they have the same general outline, but differ in some of the detail. The invasion would not be Dorian unless the invaders had some relationship to the historical Dorians. The invasion is known to have displaced population to the later Attic-Ionic regions, the Greeks of this period believed there were three major divisions of all Greek people—Dorians, Aeolians, and Ionians, each with their own defining and distinctive dialects. Often non-west is called East Greek, Arcadocypriot apparently descended more closely from the Mycenaean Greek of the Bronze Age. Boeotian had come under a strong Northwest Greek influence, and can in some respects be considered a transitional dialect, thessalian likewise had come under Northwest Greek influence, though to a lesser degree. Most of the dialect sub-groups listed above had further subdivisions, generally equivalent to a city-state and its surrounding territory, Doric notably had several intermediate divisions as well, into Island Doric, Southern Peloponnesus Doric, and Northern Peloponnesus Doric. The Lesbian dialect was Aeolic Greek and this dialect slowly replaced most of the older dialects, although Doric dialect has survived in the Tsakonian language, which is spoken in the region of modern Sparta. Doric has also passed down its aorist terminations into most verbs of Demotic Greek, by about the 6th century AD, the Koine had slowly metamorphosized into Medieval Greek
21.
Hydrophobic effect
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The hydrophobic effect is the observed tendency of nonpolar substances to aggregate in aqueous solution and exclude water molecules. The hydrophobic effect is responsible for the separation of a mixture of oil, hence the hydrophobic effect is essential to life. Substances for which this effect is observed are known as hydrophobes, amphiphiles are molecules that have both hydrophobic and hydrophilic domains. Detergents are composed of amphiphiles that allow molecules to be solubilized in water by forming micelles. They are also important to cell membranes composed of phospholipids that prevent the internal aqueous environment of a cell from mixing with external water. In the case of folding, the hydrophobic effect is important to understanding the structure of proteins that have hydrophobic amino acids clustered together within the protein. Structures of water-soluble proteins have a core in which side chains are buried from water. Charged and polar side chains are situated on the surface where they interact with surrounding water molecules. In biochemistry, the effect can be used to separate mixtures of proteins based on their hydrophobicity. To achieve better separation, a salt may be added and its concentration decreased as the separation progresses, the origin of the hydrophobic effect is not fully understood. Some argue that the interaction is mostly an entropic effect originating from the disruption of highly dynamic hydrogen bonds between molecules of liquid water by the nonpolar solute. A hydrocarbon chain or a similar region of a large molecule is incapable of forming hydrogen bonds with water. Introduction of such a non-hydrogen bonding surface into water causes disruption of the hydrogen bonding network between water molecules, the water molecules that form the cage have restricted mobility. In the solvation shell of small particles, the restriction amounts to some 10%. For example, in the case of dissolved xenon at room temperature a mobility restriction of 30% has been found, generally, this leads to significant losses in translational and rotational entropy of water molecules and makes the process unfavorable in terms of the free energy in the system. By aggregating together, nonpolar molecules reduce the area exposed to water. The hydrophobic effect can be quantified by measuring the partition coefficients of non-polar molecules between water and non-polar solvents, the partition coefficients can be transformed to free energy of transfer which includes enthalpic and entropic components, ΔG = ΔH - TΔS. These components are determined by calorimetry
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Entropy
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In statistical thermodynamics, entropy is a measure of the number of microscopic configurations Ω that a thermodynamic system can have when in a state as specified by some macroscopic variables. Formally, S = k B ln Ω, for example, gas in a container with known volume, pressure, and temperature could have an enormous number of possible configurations of the collection of individual gas molecules. Each instantaneous configuration of the gas may be regarded as random, Entropy may be understood as a measure of disorder within a macroscopic system. The second law of thermodynamics states that an isolated systems entropy never decreases, such systems spontaneously evolve towards thermodynamic equilibrium, the state with maximum entropy. Non-isolated systems may lose entropy, provided their environments entropy increases by at least that amount, since entropy is a function of the state of the system, a change in entropy of a system is determined by its initial and final states. This applies whether the process is reversible or irreversible, however, irreversible processes increase the combined entropy of the system and its environment. The above definition is called the macroscopic definition of entropy because it can be used without regard to any microscopic description of the contents of a system. The concept of entropy has found to be generally useful and has several other formulations. Entropy was discovered when it was noticed to be a quantity that behaves as a function of state and it has the dimension of energy divided by temperature, which has a unit of joules per kelvin in the International System of Units. But the entropy of a substance is usually given as an intensive property—either entropy per unit mass or entropy per unit amount of substance. In statistical mechanics this reflects that the state of a system is generally non-degenerate. Understanding the role of entropy in various processes requires an understanding of how. It is often said that entropy is an expression of the disorder, or randomness of a system, the second law is now often seen as an expression of the fundamental postulate of statistical mechanics through the modern definition of entropy. In other words, in any natural process there exists an inherent tendency towards the dissipation of useful energy and he made the analogy with that of how water falls in a water wheel. This was an insight into the second law of thermodynamics. g. Clausius described entropy as the transformation-content, i. e. dissipative energy use and this was in contrast to earlier views, based on the theories of Isaac Newton, that heat was an indestructible particle that had mass. Later, scientists such as Ludwig Boltzmann, Josiah Willard Gibbs, henceforth, the essential problem in statistical thermodynamics, i. e. according to Erwin Schrödinger, has been to determine the distribution of a given amount of energy E over N identical systems. Carathéodory linked entropy with a definition of irreversibility, in terms of trajectories
23.
Hydrogen bond
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Hydrogen bonds can occur between molecules or within different parts of a single molecule. Depending on geometry and environment, the hydrogen bond free energy content is between 1 and 5 kcal/mol and this makes it stronger than a van der Waals interaction, but weaker than covalent or ionic bonds. This type of bond can occur in molecules such as water and in organic molecules like DNA. Intermolecular hydrogen bonding is responsible for the boiling point of water compared to the other group 16 hydrides that have much weaker hydrogen bonds. Intramolecular hydrogen bonding is responsible for the secondary and tertiary structures of proteins. It also plays an important role in the structure of polymers, in 2011, an IUPAC Task Group recommended a modern evidence-based definition of hydrogen bonding, which was published in the IUPAC journal Pure and Applied Chemistry. An accompanying detailed technical report provides the rationale behind the new definition, a hydrogen atom attached to a relatively electronegative atom will play the role of the hydrogen bond donor. This electronegative atom is usually fluorine, oxygen, or nitrogen, a hydrogen attached to carbon can also participate in hydrogen bonding when the carbon atom is bound to electronegative atoms, as is the case in chloroform, CHCl3. An example of a hydrogen donor is the hydrogen from the hydroxyl group of ethanol. In a hydrogen bond, the electronegative atom not covalently attached to the hydrogen is named proton acceptor, because of the small size of hydrogen relative to other atoms and molecules, the resulting charge, though only partial, represents a large charge density. A hydrogen bond results when this positive charge density attracts a lone pair of electrons on another heteroatom. The hydrogen bond is described as an electrostatic dipole-dipole interaction. These covalent features are more substantial when acceptors bind hydrogens from more electronegative donors, the partially covalent nature of a hydrogen bond raises the following questions, To which molecule or atom does the hydrogen nucleus belong. And Which should be labeled donor and which acceptor, liquids that display hydrogen bonding are called associated liquids. Hydrogen bonds can vary in strength from weak to extremely strong. For example, the central interresidue N−H···N hydrogen bond between guanine and cytosine is much stronger in comparison to the N−H···N bond between the adenine-thymine pair, the length of hydrogen bonds depends on bond strength, temperature, and pressure. The bond strength itself is dependent on temperature, pressure, bond angle, the typical length of a hydrogen bond in water is 197 pm. The ideal bond angle depends on the nature of the hydrogen bond donor, moore and Winmill used the hydrogen bond to account for the fact that trimethylammonium hydroxide is a weaker base than tetramethylammonium hydroxide
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Clathrate compound
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A clathrate is a chemical substance consisting of a lattice that traps or contains molecules. The word clathrate is derived from the Latin clatratus meaning with bars or a lattice, traditionally, clathrate compounds are polymeric and completely envelop the guest molecule, but in modern usage clathrates also include host-guest complexes and inclusion compounds. According to IUPAC, clathrates are Inclusion compounds in which the guest molecule is in a formed by the host molecule or by a lattice of host molecules. Traditionally clathrate compounds refer to polymeric hosts containing molecular guests, more recently, the term refers to many molecular hosts, including calixarenes and cyclodextrins and even some inorganic polymers such as zeolites. The natural silica clathrate mineral, chibaite was recently described from Japan, many clathrates are derived from organic hydrogen-bonded frameworks. These frameworks are prepared from molecules that self-associate by multiple hydrogen-bonding interactions, the most famous clathrates are methane clathrates where the hydrogen-bonded framework is contributed by water and the guest molecules are methane. Large amounts of methane naturally frozen in this form exist both in permafrost formations and under the ocean sea-bed, other hydrogen-bonded networks are derived from hydroquinone, urea, and thiourea. A much studied host molecule is Dianins compound, hofmann compounds are coordination polymers with the formula Ni4Ni2. These materials crystallize with small aromatic guests, and this selectivity has been exploited commercially for the separation of these hydrocarbons, photolytically-sensitive caged compounds have been examined as containers for releasing a drug or reagent. Clathrate hydrates were discovered in 1810 by Humphry Davy, in 1945, H. M. Powell analyzed the crystal structure of these compounds and named them clathrates. Inclusion compounds are molecules, whereas clathrates are typically polymeric. Intercalation compounds are not 3-dimensional, unlike clathrate compounds
25.
Accessible surface area
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The accessible surface area or solvent-accessible surface area is the surface area of a biomolecule that is accessible to a solvent. Measurement of ASA is usually described in units of square Ångstroms, ASA was first described by Lee & Richards in 1971 and is sometimes called the Lee-Richards molecular surface. ASA is typically calculated using the rolling ball algorithm developed by Shrake & Rupley in 1973 and this algorithm uses a sphere of a particular radius to probe the surface of the molecule. The points are drawn at a water molecules estimated radius beyond the van der Waals radius, all points are checked against the surface of neighboring atoms to determine whether they are buried or accessible. The number of points accessible is multiplied by the portion of area each point represents to calculate the ASA. The choice of the probe radius does have an effect on the surface area, as using a smaller probe radius detects more surface details. A typical value is 1. 4Å, which approximates the radius of a water molecule, another factor that affects the results is the definition of the VDW radii of the atoms in the molecule under study. For example, the molecule may often lack hydrogen atoms which are implicit in the structure, the hydrogen atoms may be implicitly included in the atomic radii of the heavy atoms, with a measure called the group radii. In addition, the number of points created on the van der Waals surface of each atom determines another aspect of discretization, the LCPO method uses a linear approximation of the two-body problem for a quicker analytical calculation of ASA. The approximations used in LCPO result in an error in the range of 1-3 Ų, recently a method was presented that calculates ASA fast and analytically using a power diagram. Accessible surface area is used when calculating the transfer free energy required to move a biomolecule from aqueous solvent to a non-polar solvent such as a lipid environment. The LCPO method is used when calculating implicit solvent effects in the molecular dynamics software package AMBER. It is recently suggested that surface area can be used to improve prediction of protein secondary structure. The ASA is closely related to the concept of the solvent-excluded surface and it is also calculated in practice via a rolling-ball algorithm developed by Frederic Richards and implemented three-dimensionally by Michael Connolly in 1983 and Tim Richmond in 1984. Connolly spent several years perfecting the method. Richmond, Timothy J. solvent accessible surface area and excluded volume in proteins, Connolly, Michael L. Computation of molecular volume. Connolly, M. L. Molecular interstitial skeleton, modelling and Applications of Molecular Surfaces. Blaney, J. M. Distance Geometry in Molecular Modeling, grant, J. A. Pickup, B. T
26.
Phase (matter)
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In the physical sciences, a phase is a region of space, throughout which all physical properties of a material are essentially uniform. Examples of physical properties include density, index of refraction, magnetization, a simple description is that a phase is a region of material that is chemically uniform, physically distinct, and mechanically separable. In a system consisting of ice and water in a jar, the ice cubes are one phase, the water is a second phase. The glass of the jar is another separate phase, the term phase is sometimes used as a synonym for state of matter, but there can be several immiscible phases of the same state of matter. Also, the phase is sometimes used to refer to a set of equilibrium states demarcated in terms of state variables such as pressure and temperature by a phase boundary on a phase diagram. Distinct phases may be described as different states of such as gas, liquid, solid. Useful mesophases between solid and liquid form other states of matter, distinct phases may also exist within a given state of matter. As shown in the diagram for iron alloys, several phases exist for both the solid and liquid states, phases may also be differentiated based on solubility as in polar or non-polar. A mixture of water and oil will separate into two phases. Water has a low solubility in oil, and oil has a low solubility in water. Solubility is the amount of a solute that can dissolve in a solvent before the solute ceases to dissolve. A mixture can separate into more than two phases and the concept of phase separation extends to solids, i. e. solids can form solid solutions or crystallize into distinct crystal phases. Metal pairs that are mutually soluble can form alloys, whereas metal pairs that are mutually insoluble cannot, as many as eight immiscible liquid phases have been observed. Mutually immiscible liquid phases are formed from water, hydrophobic solvents, perfluorocarbons, silicones, several different metals. Not all organic solvents are completely miscible, e. g. a mixture of ethylene glycol, phases do not need to macroscopically separate spontaneously. Emulsions and colloids are examples of immiscible phase pair combinations that do not physically separate, left to equilibration, many compositions will form a uniform single phase, but depending on the temperature and pressure even a single substance may separate into two or more distinct phases. Within each phase, the properties are uniform but between the two phases properties differ, water in a closed jar with an air space over it forms a two phase system. Most of the water is in the phase, where it is held by the mutual attraction of water molecules
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Lotus effect
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The lotus effect refers to self-cleaning properties that are a result of ultrahydrophobicity as exhibited by the leaves of Nelumbo or lotus flower. Dirt particles are picked up by water due to the micro- and nanoscopic architecture on the surface. Ultrahydrophobicity and self-cleaning properties are found in other plants, such as Tropaeolum, Opuntia, Alchemilla, cane. The phenomenon of ultrahydrophobicity was first studied by Dettre and Johnson in 1964 using rough hydrophobic surfaces and their work developed a theoretical model based on experiments with glass beads coated with paraffin or PTFE telomer. Other biotechnical applications have emerged since the 1990s, the high surface tension of water causes droplets to assume a nearly spherical shape, since a sphere has minimal surface area, and this shape therefore demands least solid-liquid surface energy. On contact with a surface, adhesion forces result in wetting of the surface, either complete or incomplete wetting may occur depending on the structure of the surface and the fluid tension of the droplet. The cause of self-cleaning properties is the hydrophobic water-repellent double structure of the surface and this enables the contact area and the adhesion force between surface and droplet to be significantly reduced resulting in a self-cleaning process. This hierarchical double structure is formed out of a characteristic epidermis, the epidermis of the lotus plant possesses papillae with 10 µm to 20 µm in height and 10 µm to 15 µm in width on which the so-called epicuticular waxes are imposed. These superimposed waxes are hydrophobic and form the layer of the double structure. This bio-chemical property is responsible for the functioning of the water repellency of the surface, the hydrophobicity of a surface can be measured by its contact angle. The higher the angle the higher the hydrophobicity of a surface. Surfaces with a contact angle < 90° are referred to as hydrophilic, some plants show contact angles up to 160° and are called ultrahydrophobic, meaning that only 2–3% of the surface of a droplet is in contact. Plants with a double structured surface like the lotus can reach a contact angle of 170°, all this leads to a self-cleaning effect. Dirt particles with a reduced contact area are picked up by water droplets and are thus easily cleaned off the surface. If a water droplet rolls across such a surface the adhesion between the dirt particle, irrespective of its chemistry, and the droplet is higher than between the particle and the surface. As this self-cleaning effect is based on the surface tension of water it does not work with organic solvents. Therefore, the hydrophobicity of a surface is no protection against graffiti, another positive effect of self-cleaning is the prevention of contamination of the area of a plant surface exposed to light resulting in reduced photosynthesis. This can usually be achieved using special fluorochemical or silicone treatments on structured surfaces or with compositions containing micro-scale particulates, in addition to chemical surface treatments, which can be removed over time, metals have been sculpted with femtosecond pulse lasers to produce the lotus effect
28.
Interfacial tension
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Surface tension is the elastic tendency of a fluid surface which makes it acquire the least surface area possible. Surface tension allows insects, usually denser than water, to float, at liquid-air interfaces, surface tension results from the greater attraction of liquid molecules to each other than to the molecules in the air. The net effect is a force at its surface that causes the liquid to behave as if its surface were covered with a stretched elastic membrane. Thus, the surface becomes under tension from the imbalanced forces, because of the relatively high attraction of water molecules for each other through a web of hydrogen bonds, water has a higher surface tension compared to that of most other liquids. Surface tension is an important factor in the phenomenon of capillarity, Surface tension has the dimension of force per unit length, or of energy per unit area. The two are equivalent, but when referring to energy per unit of area, it is common to use the surface energy. In materials science, surface tension is used for either surface stress or surface free energy, the cohesive forces among liquid molecules are responsible for the phenomenon of surface tension. In the bulk of the liquid, each molecule is pulled equally in every direction by neighboring liquid molecules, the molecules at the surface do not have the same molecules on all sides of them and therefore are pulled inwards. This creates some internal pressure and forces liquid surfaces to contract to the minimal area, Surface tension is responsible for the shape of liquid droplets. Although easily deformed, droplets of water tend to be pulled into a shape by the imbalance in cohesive forces of the surface layer. In the absence of forces, including gravity, drops of virtually all liquids would be approximately spherical. The spherical shape minimizes the necessary wall tension of the surface according to Laplaces law. Another way to view surface tension is in terms of energy, a molecule in contact with a neighbor is in a lower state of energy than if it were alone. The interior molecules have as many neighbors as they can possibly have, for the liquid to minimize its energy state, the number of higher energy boundary molecules must be minimized. The minimized quantity of boundary molecules results in a surface area. As a result of surface area minimization, a surface will assume the smoothest shape it can, since any curvature in the surface shape results in greater area, a higher energy will also result. Consequently, the surface will push back against any curvature in much the way as a ball pushed uphill will push back to minimize its gravitational potential energy. Bubbles in pure water are unstable, the addition of surfactants, however, can have a stabilizing effect on the bubbles
29.
Goniometer
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A goniometer is an instrument that either measures an angle or allows an object to be rotated to a precise angular position. The term goniometry is derived from two Greek words, gōnia, meaning angle, and metron, meaning measure, the first description of a goniometer, derived from the astrolabe, was apparently in 1538, by Gemma Frisius. Prior to the invention of the theodolite, the goniometer was used in surveying, the Bellini–Tosi direction finder was a type of radio direction finder that was widely used from World War I to World War II. It used the signals from two crossed antennas, or four individual antennas simulating two crossed ones, to re-create the radio signal in an area between two loops of wire. The operator could measure the angle to the target radio source by performing direction finding within this small area. The advantage to the Bellini–Tosi system is that the antennas do not move, the basic technique remains in use, although the equipment has changed dramatically. Goniometers are widely used for military and civil purposes, e. g. interception of satellite, in crystallography, goniometers are used for measuring angles between crystal faces. They are also used in X-ray diffraction to rotate the samples, the groundbreaking investigations of physicist Max von Laue and colleagues into the atomic structure of crystals in 1912 involved a goniometer. Goniophotometers measure the distribution of light visible to the human eye at a specific angular position. A goniometer is used to document initial and subsequent range of motion, at the visits for occupational injuries and this is to evaluate progress, and also for medico-legal purposes. It is a tool to evaluate Waddells signs In physical therapy and occupational therapy and this measurement instrument is a helpful, clinical tool that allows for objective measurements in order to accurately track progress in a rehabilitation program. When a patient has a range of motion, a therapist will assess the joint before performing an intervention. These range of measurements can be taken at any joint and they typically involve some knowledge about the anatomy of the body. For example, when measuring the knee joint, the axis would be placed on the lateral epicondyle of the femur, while the stationary arm would be lined up with the greater trochanter of the femur. Finally, the arm of the goniometer would be lined up with the lateral malleolus of the fibula. The only problem with goniometers is the accuracy of the reading is not always the greatest, issues with the intra-measure and inter-tester reliability seem to increase as the experience of the examiner decreases. Some studies suggest that these errors can be anywhere between 5 and 10 degrees when completing repeated measures and these goniometers do come in different forms that some would argue will actually increase the reliability of the tool. The universal standard goniometer is a plastic or metal tool with 1 degree increments, the arms usually are not longer than 12-inches so it can be hard to accurately pinpoint the exact landmark needed for measurement
30.
Nanotechnology
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Nanotechnology is manipulation of matter on an atomic, molecular, and supramolecular scale. It is therefore common to see the plural form nanotechnologies as well as nanoscale technologies to refer to the range of research. Because of the variety of applications, governments have invested billions of dollars in nanotechnology research. Until 2012, through its National Nanotechnology Initiative, the USA has invested 3.7 billion dollars, scientists currently debate the future implications of nanotechnology. Nanotechnology may be able to create new materials and devices with a vast range of applications, such as in nanomedicine, nanoelectronics, biomaterials energy production. These concerns have led to a debate among advocacy groups and governments on whether regulation of nanotechnology is warranted. The term nano-technology was first used by Norio Taniguchi in 1974, also in 1986, Drexler co-founded The Foresight Institute to help increase public awareness and understanding of nanotechnology concepts and implications. In the 1980s, two major breakthroughs sparked the growth of nanotechnology in modern era, the microscopes developers Gerd Binnig and Heinrich Rohrer at IBM Zurich Research Laboratory received a Nobel Prize in Physics in 1986. Binnig, Quate and Gerber also invented the atomic force microscope that year. Second, Fullerenes were discovered in 1985 by Harry Kroto, Richard Smalley, and Robert Curl, in the early 2000s, the field garnered increased scientific, political, and commercial attention that led to both controversy and progress. Controversies emerged regarding the definitions and potential implications of nanotechnologies, exemplified by the Royal Societys report on nanotechnology, challenges were raised regarding the feasibility of applications envisioned by advocates of molecular nanotechnology, which culminated in a public debate between Drexler and Smalley in 2001 and 2003. Meanwhile, commercialization of products based on advancements in nanoscale technologies began emerging and these products are limited to bulk applications of nanomaterials and do not involve atomic control of matter. Governments moved to promote and fund research into nanotechnology, such as in the U. S, by the mid-2000s new and serious scientific attention began to flourish. Projects emerged to produce nanotechnology roadmaps which center on atomically precise manipulation of matter and discuss existing and projected capabilities, goals, Nanotechnology is the engineering of functional systems at the molecular scale. This covers both current work and concepts that are more advanced, one nanometer is one billionth, or 10−9, of a meter. By comparison, typical carbon-carbon bond lengths, or the spacing between atoms in a molecule, are in the range 0. 12–0.15 nm. On the other hand, the smallest cellular life-forms, the bacteria of the genus Mycoplasma, are around 200 nm in length, by convention, nanotechnology is taken as the scale range 1 to 100 nm following the definition used by the National Nanotechnology Initiative in the US. The lower limit is set by the size of atoms since nanotechnology must build its devices from atoms and molecules
31.
Electrowetting
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Electrowetting is the modification of the wetting properties of a surface with an applied electric field. The electrowetting behavior of mercury and other liquids on variably charged surfaces was probably first explained by Gabriel Lippmann in 1875 and was observed much earlier. Frumkin used surface charge to change the shape of water drops in 1936, the term electrowetting was first introduced in 1981 by G. Beni and S. Hackwood to describe an effect proposed for designing a new type of display device for which they received a patent. The use of a transistor in microfluidic circuits for manipulating chemical and biological fluids was first investigated by J. Later. Silver at the NIH, EWOD-based electrowetting was disclosed for single and immiscible fluids to move, separate, hold, Electrowetting using an insulating layer on top of the bare electrodes was later studied by Bruno Berge in 1993. Electrowetting on this surface is called electrowetting-on-dielectric to distinguish it from the conventional electrowetting on the bare electrode. Microfluidic manipulation of liquids by electrowetting was demonstrated first with mercury droplets in water and later with water in air, manipulation of droplets on a two-dimensional path was demonstrated later. If the liquid is discretized and programmably manipulated, the approach is called Digital Microfluidic Circuits or Digital Microfluidics, the phenomenon of electrowetting can be understood in terms of the forces that result from the applied electric field. The fringing field at the corners of the droplet tends to pull the droplet down onto the electrode, lowering the macroscopic contact angle. Alternatively, electrowetting can be viewed from a thermodynamic perspective, the chemical component is just the natural surface tension of the solid/electrolyte interface with no electric field. The electrical component is the energy stored in the capacitor formed between the conductor and the electrolyte, the simplest derivation of electrowetting behavior is given by considering its thermodynamic model. The thermodynamic derivation proceeds as follows, however, surface charge is but one component of surface energy, and other components are certainly perturbed by induced charge. So, an explanation of electrowetting is unquantified, but it should not be surprising that these limits exist. It was recently shown by Klarman et al, within this framework it is predicted that reversed electrowetting is also possible. This same paper further suggests that electrohydrodynamic instability may be the source of saturation, reverse electrowetting can be used to harvest energy via a mechanical-to-electrical engineering scheme. Another electrowetting configuration is electrowetting on liquid-infused film, the liquid-infused film is achieved by locking a liquid lubricant in a porous membrane through the delicate control of wetting properties of the liquid and solid phases. Meanwhile, the effect associated with the EWOLF can be tailored by manipulating the viscosity. Optoelectrowetting, and photoelectrowetting are both optically-induced electrowetting effects, by optically modulating the number of carriers in the space-charge region of the semiconductor, the contact angle of a liquid droplet can be altered in a continuous way
32.
Dimer (chemistry)
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A dimer is an oligomer consisting of two structurally similar monomers joined by bonds that can be either strong or weak, covalent or intermolecular. The term homodimer is used when the two molecules are identical and heterodimer when they are not, the reverse of dimerisation is often called dissociation. Carboxylic acids form dimers by hydrogen bonding of the acidic hydrogen, for example, acetic acid forms a dimer in the gas phase, where the monomer units are held together by hydrogen bonds. Under special conditions, most OH-containing molecules form dimers, e. g. the water dimer, borane occurs as the dimer diborane, due to the high Lewis acidity of the boron center. Excimers and exciplexes are excited structures with a short lifetime, for example, noble gases do not form stable dimers, but do form the excimers Ar2*, Kr2* and Xe2* under high pressure and electrical stimulation. Molecular dimers are formed by the reaction of two identical compounds e. g. 2A → A-A. In this example, monomer A is said to dimerise to give the dimer A-A, an example is a diaminocarbene, which dimerise to give a tetraaminoethylene,2 C2 → 2C=C2 Carbenes are highly reactive and readily form bonds. Dicyclopentadiene is a dimer of two cyclopentadiene molecules that have reacted in a Diels-Alder reaction to give the product. Upon heating, it cracks to give monomers, C10H12 →2 C5H6 Many nonmetallic elements occur as dimers, hydrogen, nitrogen, oxygen. Mercury occurs as a cation, formally a heterodimer. In the context of polymers, dimer also refers to the degree of polymerization 2, regardless of the stoichiometry or condensation reactions. For example, cellobiose is a dimer of glucose, even though the formation reaction produces water, 2C6H12O6 → C12H22O11 + H2O Here, amino acids can also form dimers, which are called dipeptides. An example is glycylglycine, consisting of two glycine molecules joined by a peptide bond, other examples are aspartame and carnosine. Pyrimidine dimers are formed by a reaction from pyrimidine DNA bases. This cross-linking causes DNA mutations, which can be carcinogenic, causing skin cancers, monomer Trimer Polymer Protein dimer IUPAC Gold Book definition
33.
Bionics
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Bionics is the application of biological methods and systems found in nature to the study and design of engineering systems and modern technology. The word bionic was coined by Jack E. Steele in 1958, possibly originating from the technical term bion, meaning unit of life, some dictionaries, however, explain the word as being formed as a portmanteau from biology and electronics. It was popularized by the 1970s U. S. television series The Six Million Dollar Man and The Bionic Woman, all feature humans given superhuman powers by electromechanical implants. A classical example is the development of dirt- and water-repellent paint from the observation that the surface of the lotus flower plant is practically unsticky for anything, the term biomimetic is preferred when reference is made to chemical reactions. In that domain, biomimetic chemistry refers to reactions that, in nature, examples of bionics in engineering include the hulls of boats imitating the thick skin of dolphins, sonar, radar, and medical ultrasound imaging imitating animal echolocation. In the field of science, the study of bionics has produced artificial neurons, artificial neural networks. Evolutionary computation was also motivated by ideas but it took the idea further by simulating evolution in silico. The name biomimetics was coined by Otto Schmitt in the 1950s, the term bionics was coined by Jack E. Steele in 1958 while working at the Aeronautics Division House at Wright-Patterson Air Force Base in Dayton, Ohio. However, terms like biomimicry or biomimetics are more preferred in the world in efforts to avoid confusion between the medical term bionics. Coincidentally, Martin Caidin used the word for his 1972 novel Cyborg, Caidin was a long-time aviation industry writer before turning to fiction full-time. Often, the study of bionics emphasizes implementing a function found in rather than just imitating biological structures. The conscious copying of examples and mechanisms from natural organisms and ecologies is a form of applied case-based reasoning, treating nature itself as a database of solutions that already work, proponents argue that the selective pressure placed on all natural life forms minimizes and removes failures. In robotics, bionics and biomimetics are used to apply the way animals move to the design of robots, bionicKangaroo was based on the movements and physiology of kangaroos. Velcro is the most famous example of biomimetics, in 1948, the Swiss engineer George de Mestral was cleaning his dog of burrs picked up on a walk when he realized how the hooks of the burrs clung to the fur. It revolutionized the industry because the blades worked so much faster at felling trees, cats eye reflectors were invented by Percy Shaw in 1935 after studying the mechanism of cat eyes. He had found that cats had a system of reflecting cells, known as tapetum lucidum, leonardo da Vincis flying machines and ships are early examples of drawing from nature in engineering. Resilin is a replacement for rubber that has created by studying the material also found in arthropods. Julian Vincent drew from the study of pinecones when he developed in 2004 smart clothing that adapts to changing temperatures, I wanted a nonliving system which would respond to changes in moisture by changing shape, he said
34.
Vanadium(V) oxide
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Vanadium oxide is the inorganic compound with the formula V2O5. Commonly known as vanadium pentoxide, it is a solid, although when freshly precipitated from aqueous solution. Because of its oxidation state, it is both an amphoteric oxide and an oxidizing agent. From the industrial perspective, it is the most important compound of vanadium, the mineral form of this compound, shcherbinaite, is extremely rare, almost always found among fumaroles. A mineral trihydrate, V2O5·3H2O, is known under the name of navajoite. Upon heating, it reversibly loses oxygen, successively forming V2O4, V2O3, VO, unlike most metal oxides, it dissolves slightly in water to give a pale yellow, acidic solution. When this compound is formed by V2O5 it is an amphoteric oxide, if excess aqueous sodium hydroxide is used, the product is a colourless salt, sodium orthovanadate, Na3VO4. If acid is added to a solution of Na3VO4, the colour gradually deepens through orange to red before brown hydrated V2O5 precipitates around pH2. These solutions contain mainly the ions HVO42− and V2O74− between pH9 and pH13, but below pH9 more exotic species such as V4O124− and this conversion illustrates the redox properties of V2O5. Further reduction using hydrogen or excess CO can lead to complex mixtures of such as V4O7. Vanadates or vanadyl compounds in solution are reduced by zinc amalgam through the interestingly colourful pathway, The ions are, of course. Technical grade V2O5 is produced as a powder used for the production of vanadium metal. A vanadium ore or vanadium-rich residue is treated with sodium carbonate to produce sodium metavanadate and this material is then acidified to pH 2–3 using H2SO4 to yield a precipitate of red cake. The red cake is then melted at 690 °C to produce the crude V2O5, Vanadium oxide is produced when vanadium metal is heated with excess oxygen, but this product is contaminated with other, lower oxides. The oxide is heated with iron and ferrosilicon, with lime added to form a calcium silicate slag. Aluminium may also be used, producing the iron-vanadium alloy along with alumina as a by-product, the reaction is performed between 400 and 620 °C, below 400 °C the V2O5 is inactive as a catalyst, and above 620 °C it begins to break down. Maleic anhydride is produced by the V2O5-catalysed oxidation of butane with air, C4H10 +4 O2 → C2H22O +8 H2O Maleic anhydride is used for the production of polyester resins, Phthalic anhydride is produced similarly by V2O5-catalysed oxidation of ortho-xylene or naphthalene at 350–400 °C. The equation is for the oxidation, C6H42 +3 O2 → C6H42O +3 H2O Phthalic anhydride is a precursor to plasticisers
35.
Inkjet printing
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Inkjet printing is a type of computer printing that recreates a digital image by propelling droplets of ink onto paper, plastic, or other substrates. Inkjet printers are the most commonly used type of printer, the concept of inkjet printing originated in the 20th century, and the technology was first extensively developed in the early 1950s. Starting in the late 1970s inkjet printers that could reproduce digital images generated by computers were developed, mainly by Epson, Hewlett-Packard, in the worldwide consumer market, four manufacturers account for the majority of inkjet printer sales, Canon, HP, Epson, and Brother. The emerging ink jet material deposition market also uses inkjet technologies, typically printheads using piezoelectric crystals, the technology has been extended and the ″ink″ can now also comprise living cells, for creating biosensors and for tissue engineering. There are two main technologies in use in contemporary inkjet printers, continuous and Drop-on-demand, the continuous inkjet method is used commercially for marking and coding of products and packages. In 1867 Lord Kelvin patented the syphon recorder, which recorded telegraph signals as a trace on paper using an ink jet nozzle deflected by a magnetic coil. The first commercial devices were introduced in 1951 by Siemens, the ink droplets are subjected to an electrostatic field created by a charging electrode as they form, the field varies according to the degree of drop deflection desired. This results in a controlled, variable electrostatic charge on each droplet, charged droplets are separated by one or more uncharged guard droplets to minimize electrostatic repulsion between neighbouring droplets. The more highly charged droplets are deflected to a greater degree, only a small fraction of the droplets is used to print, the majority being recycled. CIJ is one of the oldest ink jet technologies in use and is fairly mature, viscosity is monitored and a solvent is added to counteract solvent loss. Drop-on-demand is divided into thermal DOD and piezoelectric DOD, most consumer inkjet printers, including those from Canon, Hewlett-Packard, and Lexmark, use the thermal inkjet process. Vaughts work started in late 1978 with a project to develop fast, low-cost printing, the team at HP found that thin-film resistors could produce enough heat to fire an ink droplet. Two years later the HP and Canon teams found out about each others work, in the thermal inkjet process, the print cartridges consist of a series of tiny chambers, each containing a heater, all of which are constructed by photolithography. The inks involved are usually water-based and use either pigments or dyes as the colorant, the inks must have a volatile component to form the vapor bubble, otherwise droplet ejection cannot occur. As no special materials are required, the print head is generally cheaper to produce than in other inkjet technologies, most commercial and industrial inkjet printers and some consumer printers use a piezoelectric material in an ink-filled chamber behind each nozzle instead of a heating element. When a voltage is applied, the material changes shape, generating a pressure pulse in the fluid. A DOD process uses software that directs the heads to apply between zero and eight droplets of ink per dot, only where needed, piezo inkjet technology is often used on production lines to mark products. For instance, the date is often applied to products with this technique, in this application the head is stationary
36.
Carrier generation and recombination
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In the solid-state physics of semiconductors, carrier generation and recombination are processes by which mobile charge carriers are created and eliminated. Carrier generation and recombination processes are fundamental to the operation of many semiconductor devices, such as photodiodes, LEDs. They are also critical to a analysis of p-n junction devices such as bipolar junction transistors. Like other solids, semiconductor materials have a band structure determined by the crystal properties of the material. The actual energy distribution among the electrons is described by the Fermi level, at absolute zero temperature, all of the electrons have energy below the Fermi level, but at non-zero temperatures the energy levels are filled following a Boltzmann distribution. In semiconductors the Fermi level lies in the middle of a band or band gap between two allowed bands called the valence band and the conduction band. The valence band, immediately below the band, is normally very nearly completely occupied. The conduction band, above the Fermi level, is nearly completely empty. Because the valence band is so full, its electrons are not mobile. However, if an electron in the valence band acquires enough energy to reach the conduction band, furthermore, it will also leave behind an electron hole that can flow as current exactly like a physical charged particle. In a material at thermal equilibrium generation and recombination are balanced, the equilibrium carrier density that results from the balance of these interactions is predicted by thermodynamics. The resulting probability of occupation of states in each energy band is given by Fermi–Dirac statistics. Recombination and generation are happening in semiconductors, both optically and thermally, and their rates are in balance at equilibrium. The product of the electron and hole densities is a constant at equilibrium, when there is a surplus of carriers, the rate of recombination becomes greater than the rate of generation, driving the system back towards equilibrium. Likewise, when there is a deficit of carriers, the rate becomes greater than the recombination rate. As the electron moves from one band to another, the energy. The following models are used to describe generation and recombination, depending on which particles are involved in the process, the localized state can absorb differences in momentum between the carriers, and so this process is the dominant generation and recombination process in silicon and other indirect bandgap materials. It can also dominate in direct bandgap materials under conditions of very low carrier densities, the energy is exchanged in the form of lattice vibration, a phonon exchanging thermal energy with the material
37.
Titanium dioxide
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Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemical formula TiO2. When used as a pigment, it is called white, Pigment White 6. Generally it is sourced from ilmenite, rutile and anatase and it has a wide range of applications, from paint to sunscreen to food coloring. When used as a coloring, it has E number E171. World production in 2014 exceeded 9 million metric tons, one of these is known as akaogiite and should be considered as an extremely rare mineral. It is mainly sourced from ilmenite ore and this is the most widespread form of titanium dioxide-bearing ore around the world. Rutile is the next most abundant and contains around 98% titanium dioxide in the ore, the metastable anatase and brookite phases convert irreversibly to the equilibrium rutile phase upon heating above temperatures in the range 600–800 °C. Dubrovinsky and co-authors to be the hardest known oxide with the Vickers hardness of 38 GPa, however, later studies came to different conclusions with much lower values for both the hardness and bulk modulus. The oxides are commercially important ores of titanium, the metal can also be mined from other minerals such as ilmenite or leucoxene ores, or one of the purest forms, rutile beach sand. Star sapphires and rubies get their asterism from rutile impurities present in them, Titanium dioxide is found as a mineral in magmatic rocks and hydrothermal veins, as well as weathering rims on perovskite. TiO2 also forms lamellae in other minerals, spectral lines from titanium oxide are prominent in class M stars, which are cool enough to allow molecules of this chemical to form. The production method depends on the feedstock, the most common method for the production of titanium dioxide utilizes the mineral ilmenite. Ilmenite is mixed with sulfuric acid and this reacts to remove the iron oxide group in the ilmenite. The by-product iron sulfate is crystallized and filtered-off to yield only the salt in the digestion solution. This product is called synthetic rutile and this is further processed in a similar way to rutile to give the titanium dioxide product. Synthetic rutile and titanium slags are made especially for titanium dioxide production, the use of ilminite ore usually only produces pigment grade titanium dioxide. Another method for the production of synthetic rutile from ilmenite utilizes the Becher Process, rutile is the second most abundant mineral sand. Rutile found in primary rock cannot be extracted hence the deposits containing rutile sand can be mined meaning a reduced availability to the high concentration ore, crude titanium dioxide is purified via converting to titanium tetrachloride in the chloride process
38.
Sol-gel
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In materials science, the sol-gel process is a method for producing solid materials from small molecules. The method is used for the fabrication of metal oxides, especially the oxides of silicon, the process involves conversion of monomers into a colloidal solution that acts as the precursor for an integrated network of either discrete particles or network polymers. In the case of the colloid, the fraction of particles may be so low that a significant amount of fluid may need to be removed initially for the gel-like properties to be recognized. This can be accomplished in any number of ways, the simplest method is to allow time for sedimentation to occur, and then pour off the remaining liquid. Centrifugation can also be used to accelerate the process of phase separation, removal of the remaining liquid phase requires a drying process, which is typically accompanied by a significant amount of shrinkage and densification. The rate at which the solvent can be removed is determined by the distribution of porosity in the gel. The ultimate microstructure of the component will clearly be strongly influenced by changes imposed upon the structural template during this phase of processing. One of the advantages of using this methodology as opposed to the more traditional processing techniques is that densification is often achieved at a much lower temperature. The precursor sol can be deposited on a substrate to form a film, cast into a suitable container with the desired shape. The sol-gel approach is a cheap and low-temperature technique that allows for the control of the product’s chemical composition. Even small quantities of dopants, such as dyes and rare earth elements, can be introduced in the sol. It can be used in processing and manufacturing as an investment casting material. Sol-gel derived materials have applications in optics, electronics, energy, space, sensors, medicine, reactive material. Sol-gel research grew to be so important that in the 1990s more than 35,000 papers were published worldwide on the process, the sol-gel process is a wet-chemical technique used for the fabrication of both glassy and ceramic materials. In this process, the sol evolves gradually towards the formation of a network containing both a liquid phase and a solid phase. Typical precursors are metal alkoxides and metal chlorides, which undergo hydrolysis, the basic structure or morphology of the solid phase can range anywhere from discrete colloidal particles to continuous chain-like polymer networks. The term colloid is used primarily to describe a range of solid-liquid mixtures. The term is specific to the size of the individual particles, if the particles are large enough, then their dynamic behavior in any given period of time in suspension would be governed by forces of gravity and sedimentation
