In organic chemistry, a hydrocarbon is an organic compound consisting of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls; because carbon has 4 electrons in its outermost shell carbon has four bonds to make, is only stable if all 4 of these bonds are used. Aromatic hydrocarbons, alkanes and alkyne-based compounds are different types of hydrocarbons. Most hydrocarbons found on Earth occur in crude oil, where decomposed organic matter provides an abundance of carbon and hydrogen which, when bonded, can catenate to form limitless chains; as defined by IUPAC nomenclature of organic chemistry, the classifications for hydrocarbons are: Saturated hydrocarbons are the simplest of the hydrocarbon species. They are composed of single bonds and are saturated with hydrogen; the formula for acyclic saturated hydrocarbons is CnH2n+2. The most general form of saturated hydrocarbons is CnH2n +2.
Those with one ring are the cycloalkanes. Saturated hydrocarbons are the basis of petroleum fuels and are found as either linear or branched species. Substitution reaction is their characteristics property. Hydrocarbons with the same molecular formula but different structural formulae are called structural isomers; as given in the example of 3-methylhexane and its higher homologues, branched hydrocarbons can be chiral. Chiral saturated hydrocarbons constitute the side chains of biomolecules such as chlorophyll and tocopherol. Unsaturated hydrocarbons have one or more triple bonds between carbon atoms; those with double bond are called alkenes. Those with one double bond have the formula CnH2n; those containing triple bonds are called alkyne. Those with one triple bond have the formula CnH2n−2. Aromatic hydrocarbons known as arenes, are hydrocarbons that have at least one aromatic ring. Hydrocarbons can be gases, waxes or low melting solids or polymers; because of differences in molecular structure, the empirical formula remains different between hydrocarbons.
This inherent ability of hydrocarbons to bond to themselves is known as catenation, allows hydrocarbons to form more complex molecules, such as cyclohexane, in rarer cases, arenes such as benzene. This ability comes from the fact that the bond character between carbon atoms is non-polar, in that the distribution of electrons between the two elements is somewhat due to the same electronegativity values of the elements, does not result in the formation of an electrophile. With catenation comes the loss of the total amount of bonded hydrocarbons and an increase in the amount of energy required for bond cleavage due to strain exerted upon the molecule. In simple chemistry, as per valence bond theory, the carbon atom must follow the 4-hydrogen rule, which states that the maximum number of atoms available to bond with carbon is equal to the number of electrons that are attracted into the outer shell of carbon. In terms of shells, carbon consists of an incomplete outer shell, which comprises 4 electrons, thus has 4 electrons available for covalent or dative bonding.
Hydrocarbons are hydrophobic like lipids. Some hydrocarbons are abundant in the solar system. Lakes of liquid methane and ethane have been found on Titan, Saturn's largest moon, confirmed by the Cassini-Huygens Mission. Hydrocarbons are abundant in nebulae forming polycyclic aromatic hydrocarbon compounds. Hydrocarbons are a primary energy source for current civilizations; the predominant use of hydrocarbons is as a combustible fuel source. In their solid form, hydrocarbons take the form of asphalt. Mixtures of volatile hydrocarbons are now used in preference to the chlorofluorocarbons as a propellant for aerosol sprays, due to chlorofluorocarbons' impact on the ozone layer. Methane and ethane are gaseous at ambient temperatures and cannot be liquefied by pressure alone. Propane is however liquefied, exists in'propane bottles' as a liquid. Butane is so liquefied that it provides a safe, volatile fuel for small pocket lighters. Pentane is a colorless liquid at room temperature used in chemistry and industry as a powerful nearly odorless solvent of waxes and high molecular weight organic compounds, including greases.
Hexane is a used non-polar, non-aromatic solvent, as well as a significant fraction of common gasoline. The C6 through C10 alkanes and isomeric cycloalkanes are the top components of gasoline, jet fuel and specialized industrial solvent mixtures. With the progressive addition of carbon units, the simple non-ring structured hydrocarbons have higher viscosities, lubricating indices, boiling points, solidification temperatures, deeper color. At the opposite extreme from methane lie the heavy tars that remain as the lowest fraction in a crude oil refining retort, they are collected and utilized as roofing comp
The 3M Company known as the Minnesota Mining and Manufacturing Company, is an American multinational conglomerate corporation operating in the fields of industry, worker safety, health care, consumer goods. The company produces a variety of products, including adhesives, laminates, passive fire protection, personal protective equipment, window films, paint protection films and orthodontic products, electronic materials, medical products, car-care products, electronic circuits, healthcare software and optical films, it is based in Maplewood, Minnesota, a suburb of St. Paul. In 2017, 3M made $31.7 billion in total sales, the company ranked No. 97 in the 2018 Fortune 500 list of the largest United States corporations by total revenue. The company has 91,000 employees and has operations in more than 70 countries. Five businessmen founded 3M in Two Harbors, Minnesota, in 1902. A mining venture, the goal was to mine corundum, but this failed because the mine's mineral holdings were anorthosite, which had no commercial value.
Co-founder John Dwan solicited funds in exchange for stock and Edgar Ober and Lucius Ordway took over the company in 1905. The company moved to Duluth and began researching and producing sandpaper products. William L. McKnight a key executive, joined the company in 1907, A. G. Bush joined in 1909. 3M became financially stable in 1916 and was able to pay dividends. The company moved to St. Paul in 1910, where it remained for 52 years before outgrowing the campus and moving to its current headquarters at 3M Center in Maplewood, Minnesota in 1962; the company began by mining stone from quarries for use in grinding wheels. Struggling with quality and marketing of its products, management supported its workers to innovate and develop new products, which became its core business. Twelve years after its inception, 3M developed its first exclusive product: Three-M-ite cloth. Other innovations in this era included masking tape, waterproof sandpaper, Scotch-brand tapes. By 1929, 3M had made its first moves toward international expansion by forming Durex to conduct business in Europe.
The same year, the company's stock was first traded over the counter and in 1946 listed on the New York Stock Exchange. The company is a component of the Dow Jones Industrial Average and of the S&P 500; the founders original plan was to sell the mineral corundum to manufacturers in the East for making grinding wheels. After selling one load, on June 13, 1902, the five went to the Two Harbors office of company secretary John Dwan, on the shore of Lake Superior and is now part of the 3M National Museum, signed papers making Minnesota Mining and Manufacturing a corporation. In reality, however and his associates were not selling what they thought. Failing to make sandpaper with the anorthosite, the founders decided to import minerals like Spanish garnet, after which sale of sandpapers grew. In 1914, customers complained that the garnet was falling off the paper; the founders discovered that the stones had traveled across the Atlantic Ocean packed near olive oil, the oil had penetrated the stones.
Unable to take the loss of selling expensive inventory, they roasted the stones over fire to remove the olive oil. The company's late innovations include waterproof sandpaper and masking tape, as well as cellophane "Scotch Tape" and sound-deadening materials for cars. In 1947, 3M began producing perfluorooctanoic acid by electrochemical fluorination. During the 1950s, the company expanded worldwide with operations in Canada, France, Germany and the United Kingdom in large part by Clarence Sampair. In 1951, DuPont started purchasing PFOA from then-Minnesota Mining and Manufacturing Company for use in the manufacturing of teflon, a product that brought DuPont a billion-dollar-a-year profit by the 1990s. DuPont referred to PFOA as C8. In 1951, international sales were $20 million. 3M's achievements were recognized by the American Institute of Management naming the company "one of the five best-managed companies in the United States" and included it among the top 12 growth stocks. In the late 1960s and early 1970s, 3M published a line of board games under the "3M bookshelf game series" brand.
These games were marketed to adults and sold through department stores, with learned simple rules but complex game play and depth and with uniformly high-quality components. As such, they are the ancestors of the German "Eurogames"; the games covered a variety of topics, from business and sports simulations to word and abstract strategy games. They were a major publisher at the time for influential U. S. designers Sid Sackson and Alex Randolph. In the mid-1970s, the game line was taken over by Avalon Hill. 3M's Mincom division introduced several models of magnetic tape recorders for instrumentation use and for studio sound recording. An example of the latter is the model M79 recorder, which still has a following today. 3M Mincom was involved in designing and manufacturing video production equipment for the television and video post-production industries in the 1970s and 1980s, with such items as character generators and several different models of video switchers, from models of audio and video routers to video mixers for studio production work.
3M Mincom was involved in some of the first digital audio recordings of the late 1970s to see commercial release when a prototype machine was brought to the Sound 80 studios in Minneapolis. After drawing on the experience of that prototype recorder, 3M introduced in 1979 a commercially available digital audio recording system called the "3M Digital Audio Mastering System", which
A chemical compound is a chemical substance composed of many identical molecules composed of atoms from more than one element held together by chemical bonds. A chemical element bonded to an identical chemical element is not a chemical compound since only one element, not two different elements, is involved. There are four types of compounds, depending on how the constituent atoms are held together: molecules held together by covalent bonds ionic compounds held together by ionic bonds intermetallic compounds held together by metallic bonds certain complexes held together by coordinate covalent bonds. A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service: its CAS number.
A compound can be converted to a different chemical composition by interaction with a second chemical compound via a chemical reaction. In this process, bonds between atoms are broken in both of the interacting compounds, bonds are reformed so that new associations are made between atoms. Any substance consisting of two or more different types of atoms in a fixed stoichiometric proportion can be termed a chemical compound, it follows from their being composed of fixed proportions of two or more types of atoms that chemical compounds can be converted, via chemical reaction, into compounds or substances each having fewer atoms. The ratio of each element in the compound is expressed in a ratio in its chemical formula. A chemical formula is a way of expressing information about the proportions of atoms that constitute a particular chemical compound, using the standard abbreviations for the chemical elements, subscripts to indicate the number of atoms involved. For example, water is composed of two hydrogen atoms bonded to one oxygen atom: the chemical formula is H2O.
In the case of non-stoichiometric compounds, the proportions may be reproducible with regard to their preparation, give fixed proportions of their component elements, but proportions that are not integral. Chemical compounds have a unique and defined chemical structure held together in a defined spatial arrangement by chemical bonds. Chemical compounds can be molecular compounds held together by covalent bonds, salts held together by ionic bonds, intermetallic compounds held together by metallic bonds, or the subset of chemical complexes that are held together by coordinate covalent bonds. Pure chemical elements are not considered chemical compounds, failing the two or more atom requirement, though they consist of molecules composed of multiple atoms. Many chemical compounds have a unique numerical identifier assigned by the Chemical Abstracts Service: its CAS number. There is varying and sometimes inconsistent nomenclature differentiating substances, which include non-stoichiometric examples, from chemical compounds, which require the fixed ratios.
Many solid chemical substances—for example many silicate minerals—are chemical substances, but do not have simple formulae reflecting chemically bonding of elements to one another in fixed ratios. It may be argued that they are related to, rather than being chemical compounds, insofar as the variability in their compositions is due to either the presence of foreign elements trapped within the crystal structure of an otherwise known true chemical compound, or due to perturbations in structure relative to the known compound that arise because of an excess of deficit of the constituent elements at places in its structure. Other compounds regarded as chemically identical may have varying amounts of heavy or light isotopes of the constituent elements, which changes the ratio of elements by mass slightly. Compounds are held together through a variety of different types of bonding and forces; the differences in the types of bonds in compounds differ based on the types of elements present in the compound.
London dispersion forces are the weakest force of all intermolecular forces. They are temporary attractive forces that form when the electrons in two adjacent atoms are positioned so that they create a temporary dipole. Additionally, London dispersion forces are responsible for condensing non polar substances to liquids, to further freeze to a solid state dependent on how low the temperature of the environment is. A covalent bond known as a molecular bond, involves the sharing of electrons between two atoms; this type of bond occurs between elements that fall close to each other on the periodic table of elements, yet it is observed between some metals and nonmetals. This is due to the mechanism of this type of bond. Elements that fall close to each other on the periodic table tend to have similar electronegativities, which means they have a similar affinity for electrons. Since neither element has a stronger affinity to donate or gain electrons, it causes the elements to share electrons so both elements have a more stable octet.
Ionic bonding occurs when valence electrons are transferred between elements. Opposite to covalent bonding, this chemical bond creates two oppositely charged ions; the metals in ionic bonding
The carbon–fluorine bond is a polar covalent bond between carbon and fluorine, a component of all organofluorine compounds. It is the fourth strongest single bond in organic chemistry—behind the B-F single bond, Si-F single bond and the H-F single bond, short—due to its partial ionic character; the bond strengthens and shortens as more fluorines are added to the same carbon on a chemical compound. As such, fluoroalkanes like tetrafluoromethane are some of the most unreactive organic compounds; the high electronegativity of fluorine gives the carbon–fluorine bond a significant polarity/dipole moment. The electron density is concentrated around the fluorine, leaving the carbon electron poor; this introduces ionic character to the bond through partial charges. The partial charges on the fluorine and carbon are attractive, contributing to the unusual bond strength of the carbon–fluorine bond; the bond is labeled as "the strongest in organic chemistry," because fluorine forms the strongest single bond to carbon.
Carbon–fluorine bonds can have a bond dissociation energy of up to 544 kJ/mol. The BDE is higher than other carbon -- carbon -- hydrogen bonds. For example, the molecule represented by CH3X has a BDE of 115 kcal/mol for carbon–fluorine while values of 104.9, 83.7, 72.1, 57.6 kcal/mol represent carbon–X bonds to hydrogen, chlorine and iodine, respectively. The carbon–fluorine bond length is about 1.35 ångström. It is shorter than any other carbon–halogen bond, shorter than single carbon–nitrogen and carbon–oxygen bonds, despite fluorine having a larger atomic mass; the short length of the bond can be attributed to the ionic character/electrostatic attractions between the partial charges on carbon and fluorine. The carbon–fluorine bond length varies by several hundredths of an ångstrom depending on the hybridization of the carbon atom and the presence of other substituents on the carbon or in atoms farther away; these fluctuations can be used as indication of subtle hybridization changes and stereoelectronic interactions.
The table below shows. The variability in bond lengths and the shortening of bonds to fluorine due to their partial ionic character are observed for bonds between fluorine and other elements, have been a source of difficulties with the selection of an appropriate value for the covalent radius of fluorine. Linus Pauling suggested 64 pm, but that value was replaced by 72 pm, half of the fluorine–fluorine bond length. However, 72 pm is too long to be representative of the lengths of the bonds between fluorine and other elements, so values between 54 pm and 60 pm have been suggested by other authors. With increasing number of fluorine atoms on the same carbon the other bonds become stronger and shorter; this can be seen by the changes in bond length and strength for the fluoromethane series, as shown on the table below. The partial charge on carbon becomes more positive as fluorines are added, increasing the electrostatic interactions, ionic character, between the fluorines and carbon; when two fluorine atoms are in vicinal carbons, as in 1,2-difluoroethane, the gauche conformer is more stable than the anti conformer—this is the opposite of what would be expected and to what is observed for most 1,2-disubstituted ethanes.
In 1,2-difluoroethane, the gauche conformation is more stable than the anti conformation by 2.4 to 3.4 kJ/mole in the gas phase. This effect is not unique to the halogen fluorine, however. A related effect is the alkene cis effect. For instance, the cis isomer of 1,2-difluoroethylene is more stable than the trans isomer. There are two main explanations for the gauche effect: bent bonds. In the hyperconjugation model, the donation of electron density from the carbon–hydrogen σ bonding orbital to the carbon–fluorine σ* antibonding orbital is considered the source of stabilization in the gauche isomer. Due to the greater electronegativity of fluorine, the carbon–hydrogen σ orbital is a better electron donor than the carbon–fluorine σ orbital, while the carbon–fluorine σ* orbital is a better electron acceptor than the carbon–hydrogen σ* orbital. Only the gauche conformation allows good overlap between the better acceptor. Key in the bent bond explanation of the gauche effect in difluoroethane is the increased p orbital character of both carbon–fluorine bonds due to the large electronegativity of fluorine.
As a result, electron density builds up above and below to the left and right of the central carbon–carbon bond. The resulting reduced orbital overlap can be compensated when a gauche conformation is assumed, forming a bent bond. Of these two models, hyperconjugation is considered the principal cause behind the gauche effect in difluoroethane; the carbon–fluorine bond stretching appears in the infrared spectrum between 1000 and 1360 cm−1. The wide range is due to the sensitivity of the stretching frequency to other substituents in the molecule. Monofluorinated compounds have a strong band between 1000 and 1110 cm−1; the carbon–fluorine bands are so strong that they may obscure any carbon–hydrogen bands that might be present. Organofluorine compounds
Ethylene tetrafluoroethylene is a fluorine-based plastic. It was designed to have high corrosion strength over a wide temperature range. ETFE is a polymer and its source-based name is poly. ETFE has a high melting temperature, excellent chemical and high-energy radiation resistance properties; when burned, ETFE releases hydrofluoric acid. Useful comparison tables of PTFE against FEP, PFA and ETFE can be found on DuPont's website, listing the mechanical, chemical and vapour properties of each, side by side. ETFE is the high-strength version of the other three in this group featuring diminished capacities in other fields by comparison. Combustion of ETFE occurs in the same way as a number of other fluoropolymers, in terms of releasing hydrofluoric acid. HF is corrosive and toxic, so appropriate caution must be exercised. ETFE film is recyclable, it is prone to punctures by sharp edges and therefore used for roofs. As a film for roofing it could be stretched and still be taut if some variation in size occurs Employing heat welding, tears can be repaired with a patch or multiple sheets assembled into larger panels.
ETFE has an approximate tensile strength of 42 MPa, with a working temperature range of 89 K to 423 K. ETFE resins are resistant to ultraviolet light. An accelerated weathering test produced no signs of film deterioration. An example of its use is as pneumatic panels to cover the outside of the football stadium Allianz Arena or the Beijing National Aquatics Centre – the world's largest structure made of ETFE film; the panels of the Eden Project are made from ETFE, the Tropical Islands have a 20,000 m2 window made from this translucent material. Another key use of ETFE is for the covering of electrical and fiber-optic wiring used in high-stress, low-fume-toxicity and high-reliability situations. Aircraft and spacecraft wiring are primary examples; some small cross-section wires like the wire used for the wire-wrap technique are coated with ETFE. As a dual laminate, ETFE can be bonded with FRP as a thermoplastic liner and used in pipes and vessels for additional corrosion protection. ETFE is used in the nuclear industry for tie or cable wraps and in the aviation and aerospace industries for wire coatings.
This is because ETFE has better mechanical toughness than PTFE. In addition, ETFE exhibits a high-energy radiation resistance and can withstand moderately high temperatures for a long period. Commercially deployed brand names of ETFE include Tefzel by DuPont, Fluon by Asahi Glass Company, Neoflon ETFE by Daikin, Texlon by Vector Foiltec. Due to its high temperature resistance ETFE is used in film mode as a mold-release film. ETFE film offered by Guarniflon or Airtech International and Honeywell is used in aerospace applications such as carbon fiber pre-preg curing as a release film for molds or hot high-pressure plates. Notable buildings and designs using ETFE as a significant architectural element: Allianz Arena, Germany Beijing National Aquatics Centre, China Eden Project, United Kingdom Khan Shatyr Entertainment Center, Kazakhstan U. S. Bank Stadium, Minnesota, United States National Space Centre, United Kingdom Cuauhtémoc Stadium, Puebla, México. Midland Metropolitan Hospital, Birmingham, United Kingdom Hard Rock Stadium, Miami Gardens, United States Banc of California Stadium.
Los Angeles, Unite States Avenues Phase-III, Al-Rai, Kuwait Dworzec Tramwajowy Centrum, tram station in Łódź, Poland. Solaris, France Discovery College, Lantau Island, Hong Kong Green 18, Hong Kong Science Park, Hong Kong Pavilion, Alnwick Castle, United Kingdom BC Place, British Columbia, River Culture Pavillon The ARC, South Korea Munich's municipal waste management department, Germany Beijing National Stadium, China FestiveWalk, Resorts World at Sentosa, Singapore Dolce Vita Tejo Shopping Centre, Lisbon, Portugal roof, dedicated underground rail station at the Heathrow Airport Terminal 5, United Kingdom Manchester Victoria station concourse, United Kingdom Forsyth Barr Stadium at University Plaza, New Zealand Islazul Shopping Centre, Spain Kansas City Power & Light District, Kansas City, United States South Campus skylight structures, Art Center College of Design, California, United States Tanaka Business School, United Kingdom Tropical Islands, Germany Barnsley Interchange, United Kingdom The Mall Athens, Greece Newport railway station, United Kingdom The Elements, United Kingdom Experimental Media and Performing Arts Center, Rensselaer Polytechnic Institute, New York, United States Arena Pernambuco, Brazil Sandton City, South Africa Key West Shopping Centre, South Africa Oceanus Casino, Special Administrative Region of China.
Masdar city, Abu Dhabi, United Arab Emirates ISS Building Lancaster University Empire City Casino, New York, United States The SSE Hydro, Scotland Anaheim Regional Transportation Intermodal Center, California National Stadium, Singapore Orto Botanico di Padova Biodiversity Garden roof, Italy Guangzhou South Railway Station, China Yujiapu Railway Station, China Persian Garden, Iran Mall, Iran Anoeta Stadium, San Sebastian, Spain Ed Kaplan Family Institute for Innovation an
Van der Waals force
In molecular physics, the van der Waals force, named after Dutch scientist Johannes Diderik van der Waals, is a distance-dependent interaction between atoms or molecules. Unlike ionic or covalent bonds, these attractions do not result from a chemical electronic bond; the Van der Waals force vanishes at longer distances between interacting molecules. Van der Waals force plays a fundamental role in fields as diverse as supramolecular chemistry, structural biology, polymer science, surface science, condensed matter physics, it underlies many properties of organic compounds and molecular solids, including their solubility in polar and non-polar media. If no other force is present, the distance between atoms at which the force becomes repulsive rather than attractive as the atoms approach one another is called the van der Waals contact distance; the van der Waals force has the same origin as the Casimir effect, arising from quantum interactions with the zero-point field. The term van der; the term always includes the London dispersion force between instantaneously induced dipoles.
It is sometimes applied to the Debye force between a permanent dipole and a corresponding induced dipole or to the Keesom force between permanent molecular dipoles. Van der Waals forces include attraction and repulsions between atoms and surfaces, as well as other intermolecular forces, they differ from covalent and ionic bonding in that they are caused by correlations in the fluctuating polarizations of nearby particles. Being the weakest of the weakest chemical forces, with a strength between 0.4 and 4kJ/mol, they may still support an integral structural load when multitudes of such interactions are present. Such a force results from a transient shift in electron density; the electron density may temporarily shift more to one side of the nucleus. This generates a transient charge to which a nearby atom can be either repelled; when the interatomic distance of two atoms is greater than 0.6 nm the force is not strong enough to be observed. In the same vein, when the interatomic distance is below 0.4 nm the force becomes repulsive.
Intermolecular forces have four major contributions: A repulsive component resulting from the Pauli exclusion principle that prevents the collapse of molecules. Attractive or repulsive electrostatic interactions between permanent charges, quadrupoles, in general between permanent multipoles; the electrostatic interaction is sometimes called the Keesom interaction or Keesom force after Willem Hendrik Keesom. Induction, the attractive interaction between a permanent multipole on one molecule with an induced multipole on another; this interaction is sometimes called Debye force after Peter J. W. Debye. Dispersion, the attractive interaction between any pair of molecules, including non-polar atoms, arising from the interactions of instantaneous multipoles. Returning to nomenclature, different texts refer to different things using the term "van der Waals force"; some texts describe the van der Waals force as the totality of forces. All intermolecular/van der Waals forces are anisotropic, which means that they depend on the relative orientation of the molecules.
The induction and dispersion interactions are always attractive, irrespective of orientation, but the electrostatic interaction changes sign upon rotation of the molecules. That is, the electrostatic force can be attractive or repulsive, depending on the mutual orientation of the molecules; when molecules are in thermal motion, as they are in the gas and liquid phase, the electrostatic force is averaged out to a large extent, because the molecules thermally rotate and thus probe both repulsive and attractive parts of the electrostatic force. Sometimes this effect is expressed by the statement that "random thermal motion around room temperature can overcome or disrupt them"; the thermal averaging effect is much less pronounced for the attractive induction and dispersion forces. The Lennard-Jones potential is used as an approximate model for the isotropic part of a total van der Waals force as a function of distance. Van der Waals forces are responsible for certain cases of pressure broadening of spectral lines and the formation of van der Waals molecules.
The London-van der Waals forces are related to the Casimir effect for dielectric media, the former being the microscopic description of the latter bulk property. The first detailed calculations of this were done in 1955 by E. M. Lifshitz. A more general theory of van der Waals forces has been developed; the main characteristics of van der Waals forces are: They are weaker than normal covalent and ionic bonds. Van der Waals forces can not be saturated, they have no directional characteristic. They are all short-range forces and hence only interactions between the nearest particles need to be considered. Van der Waals attraction is greater. Van der Waals forces are independent
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that has numerous applications. The best-known brand name of PTFE-based formulas is Teflon by Chemours. Chemours is a spin-off of DuPont, which discovered the compound in 1938. Another popular brand name of PTFE is Syncolon® by Synco Chemical Corporation. PTFE is a fluorocarbon solid, as it is a high molecular weight compound consisting wholly of carbon and fluorine. PTFE is hydrophobic: neither water nor water-containing substances wet PTFE, as fluorocarbons demonstrate mitigated London dispersion forces due to the high electronegativity of fluorine. PTFE has one of the lowest coefficients of friction of any solid. PTFE is used as a non-stick coating for other cookware, it is nonreactive because of the strength of carbon–fluorine bonds, so it is used in containers and pipework for reactive and corrosive chemicals. Where used as a lubricant, PTFE reduces friction and energy consumption of machinery, it is used as a graft material in surgical interventions.
It is frequently employed as coating on catheters. PTFE was accidentally discovered in 1938 by Roy J. Plunkett while he was working in New Jersey for DuPont; as Plunkett attempted to make a new chlorofluorocarbon refrigerant, the tetrafluoroethylene gas in its pressure bottle stopped flowing before the bottle's weight had dropped to the point signaling "empty." Since Plunkett was measuring the amount of gas used by weighing the bottle, he became curious as to the source of the weight, resorted to sawing the bottle apart. He found the bottle's interior coated with a waxy white material, oddly slippery. Analysis showed that it was polymerized perfluoroethylene, with the iron from the inside of the container having acted as a catalyst at high pressure. Kinetic Chemicals patented the new fluorinated plastic in 1941, registered the Teflon trademark in 1945. By 1948, DuPont, which founded Kinetic Chemicals in partnership with General Motors, was producing over two million pounds of Teflon brand PTFE per year in Parkersburg, West Virginia.
An early use was in the Manhattan Project as a material to coat valves and seals in the pipes holding reactive uranium hexafluoride at the vast K-25 uranium enrichment plant in Oak Ridge, Tennessee. In 1954, Collette Grégoire, the wife of French engineer Marc Grégoire urged him to try the material he had been using on fishing tackle on her cooking pans, he subsequently created the first non-stick pans under the brandname Tefal. In the United States, Marion A. Trozzolo, using the substance on scientific utensils, marketed the first US-made PTFE-coated pan, "The Happy Pan", in 1961. However, Tefal was not the only company to utilize PTFE in nonstick cookware coatings. In subsequent years, many cookware manufacturers developed proprietary PTFE-based formulas, including Swiss Diamond International, which uses a diamond-reinforced PTFE formula. Other cookware companies, such as Meyer Corporation's Anolon, use Teflon nonstick coatings purchased from Chemours. Chemours is a 2015 corporate spin-off of DuPont.
In the 1990s, it was found that PTFE could be radiation cross-linked above its melting point in an oxygen-free environment. Electron beam processing is one example of radiation processing. Cross-linked PTFE has improved radiation stability; this was significant because, for many years, irradiation at ambient conditions has been used to break down PTFE for recycling. This radiation-induced chain scission allows it to be more reground and reused. PTFE is produced by free-radical polymerization of tetrafluoroethylene; the net equation is n F2C=CF2 → −n−Because tetrafluoroethylene can explosively decompose to tetrafluoromethane and carbon, special apparatus is required for the polymerization to prevent hot spots that might initiate this dangerous side reaction. The process is initiated with persulfate, which homolyzes to generate sulfate radicals: 2− ⇌ 2 SO4•−The resulting polymer is terminated with sulfate ester groups, which can be hydrolyzed to give OH end-groups; because PTFE is poorly soluble in all solvents, the polymerization is conducted as an emulsion in water.
This process gives a suspension of polymer particles. Alternatively, the polymerization is conducted using a surfactant such as PFOS. PTFE is a thermoplastic polymer, a white solid at room temperature, with a density of about 2200 kg/m3. According to Chemours, its melting point is 600 K, it maintains high strength and self-lubrication at low temperatures down to 5 K, good flexibility at temperatures above 194 K. PTFE gains its properties from the aggregate effect of carbon-fluorine bonds, as do all fluorocarbons; the only chemicals known to affect these carbon-fluorine bonds are reactive metals like the alkali metals, at higher temperatures such metals as aluminium and magnesium, fluorinating agents such as xenon difluoride and cobalt fluoride. The coefficient of friction of plastics is measured against polished steel. PTFE's coefficient of friction is 0.05 to 0.10, the third-lowest of any known solid material. PTFE's resistance to van de