Werner Kuhn (1899-1963) is a Swiss physical chemist who developed the first model of the viscosity of polymer solutions using statistical mechanics.^[1] He is known for being the first to apply Boltzmann's entropy formula:^[2] Physical chemistry is the study of the physical basis of chemical systems and processes. ... For other uses, see Viscosity (disambiguation). ... Statistical mechanics is the application of probability theory, which includes mathematical tools for dealing with large populations, to the field of mechanics, which is concerned with the motion of particles or objects when subjected to a force. ... Boltzmanns equation - carved in stone. ...

to the modeling of rubber molecules, i.e. the "rubber band entropy model", molecules which he imagined as chains of N independenly oriented links of length b with an end-to-end distance of r.^[3] This model, which resulted in the derivation of the thermal equation of state of rubber, has since been extrapolated to the entropic modeling of proteins and other conformational polymer chained molecules attached to a surface. This article is about the polymeric material. ... For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... 3D (left and center) and 2D (right) representations of the terpenoid molecule atisane. ... In physics and thermodynamics, an equation of state is a relation between state variables. ... For other uses of the term entropy, see Entropy (disambiguation) The thermodynamic entropy S, often simply called the entropy in the context of thermodynamics, is a measure of the amount of energy in a physical system that cannot be used to do work. ...

Kuhn received a degree in chemical engineering at the Eidgenössische Technische Hochschule (ETH, Federal Institute of Technology), in Zürich, and later a doctorate (1923) in physical chemistry.^[1] Chemical engineers design, construct and operate plants Chemical engineering is the branch of engineering that deals with the application of physical science (e. ... Physical chemistry, is the application of physics to macroscopic, microscopic, atomic, subatomic, and particulate phenomena in chemical systems[1] within the field of chemistry traditionally using the principles, practices and concepts of thermodynamics, quantum chemistry, statistical mechanics and kinetics. ...

Entropy model of rubber

Composition

Aside from a few natural product impurities, natural rubber is essentially a polymer of isoprene units, a hydrocarbon diene monomer. Synthetic rubber can be made as a polymer of isoprene or various other monomers. Rubber is believed to have been named by Joseph Priestley, who discovered in 1770 that dried latex rubbed out pencil marks. The material properties of natural rubber make it an elastomer and a thermoplastic. However it should be noted that as the rubber is vulcanized it will turn into a thermoset. Most rubber in everyday use is vulcanized to a point where it shares properties of both i.e. if it is heated and cooled it is degraded but not destroyed. A polymer (from Greek: πολυ, polu, many; and μέρος, meros, part) is a substance composed of molecules with large molecular mass composed of repeating structural units, or monomers, connected by covalent chemical bonds. ... Isoprene is a common synonym for the chemical compound 2-methyl-1,3-butadiene. ... A 3-dimensional rendered Ball-and-stick model of the methane molecule. ... Dienes are hydrocarbons which contain two double bonds. ... A monomer (from Greek mono one and meros part) is a small molecule that may become chemically bonded to other monomers to form a polymer [1]. // Examples of monomers are hydrocarbons such as the alkene and arene homologous series. ... Priestley by Ellen Sharples (1794)[1] Joseph Priestley (13 March 1733 (Old Style) – 6 February 1804) was an 18th-century British theologian, Dissenting clergyman, natural philosopher, educator, and political theorist who published over 150 works. ... The term elastomer is often used interchangeably with the term rubber, and is preferred when referring to vulcanisates. ... For other uses, see Plastic (disambiguation). ... Thermosetting plastics (thermosets) refer to a range of polymer materials that cure, through the addition of energy, to a stronger form. ...

Elasticity

In most elastic materials, such as metals used in springs, the elastic behavior is caused by bond distortions. When force is applied, bond lengths deviate from the (minimum energy) equilibrium and strain energy is stored electrostatically. Rubber is often assumed to behave in the same way, but it turns out this is a poor description. Rubber is a curious material because, unlike metals, strain energy is stored thermally, as well as electrostatically. For alternative meanings see metal (disambiguation). ... A compression coil spring A tension coil spring A selection of conical coil springs A Coil spring, also known as a helical spring, is a mechanical device, which is typically used to store energy and subsequently release it, to absorb shock, or to maintain a force between contacting surfaces. ... A chemical bond is the physical process responsible for the attractive interactions between atoms and molecules, and that which confers stability to diatomic and polyatomic chemical compounds. ... Electric potential is the potential energy per unit charge associated with a static (time-invariant) electric field, also called the electrostatic potential, typically measured in volts. ... In thermal physics, thermal energy is the energy portion of a system that increases with its temperature. ...

In its relaxed state rubber consists of long, coiled-up polymer chains that are interlinked at a few points. Between a pair of links each monomer can rotate freely about its neighbour. This gives each section of chain leeway to assume a large number of geometries, like a very loose rope attached to a pair of fixed points. At room temperature rubber stores enough kinetic energy so that each section of chain oscillates chaotically, like the above piece of rope being shaken violently. In chemistry, a disulfide bond is a single covalent bond derived from the coupling of thiol groups. ... For other uses, see Room temperature (disambiguation). ... The cars of a roller coaster reach their maximum kinetic energy when at the bottom of their path. ...

When rubber is stretched the "loose pieces of rope" are taut and thus no longer able to oscillate. Their kinetic energy is given off as excess heat. Therefore, the entropy decreases when going from the relaxed to the stretched state, and it increases during relaxation. This change in entropy can also be explained by the fact that a tight section of chain can fold in fewer ways (W) than a loose section of chain, at a given temperature (nb. entropy is defined as S=k*ln(W)). Relaxation of a stretched rubber band is thus driven by an increase in entropy, and the force experienced is not electrostatic, rather it is a result of the thermal energy of the material being converted to kinetic energy. Rubber relaxation is endothermic. The material undergoes adiabatic cooling during contraction. This property of rubber can easily be verified by holding a stretched rubber band to your lips and relaxing it. For other uses, see: information entropy (in information theory) and entropy (disambiguation). ... This article is about the common household item. ... This article is about the physical effect. ... This article covers adiabatic processes in thermodynamics. ...

Stretching of a rubber band is in some ways equivalent to the compression of an ideal gas, and relaxation in equivalent to its expansion. Note that a compressed gas also exhibits "elastic" properties, for instance inside an inflated car tire. The fact that stretching is equivalent to compression may seem somewhat counter-intuitive, but it makes sense if rubber is viewed as a one-dimensional gas. Stretching reduces the "space" available to each section of chain. Bold text Wiktionary has related dictionary definitions, such as: compressor, compression inthe wkjhrlfidhb;g/df == Compressor may refer to: Gas compressor, a mechanical device that compresses a gas e. ... An ideal gas or perfect gas is a hypothetical gas consisting of identical particles of zero volume, with no intermolecular forces, where the constituent atoms or molecules undergo perfectly elastic collisions with the walls of the container and each other and are in constant random motion. ... Expansion can have several meanings, including: In physics: Expansion of space In computer hardware: an Expansion card In computer programming: In-line expansion In computer gaming: an expansion pack See also: Wikipedia:Requests for expansion This is a disambiguation page — a navigational aid which lists other pages that might otherwise... Firestone tire This article is about pneumatic tires. ...

Vulcanization of rubber creates more disulphide bonds between chains so it makes each free section of chain shorter. The result is that the chains tighten more quickly for a given length of strain. This increases the elastic force constant and makes rubber harder and less extendable. Vulcanization refers to a specific curing process of rubber involving high heat and the addition of sulfur. ... A disulfide bond (SS-bond), also called a disulfide bridge, is a strong covalent bond between two sulfhydryl groups. ... This article is about the deformation of materials. ...

When cooled below the glass transition temperature, the quasi-fluid chain segments "freeze" into fixed geometries and the rubber abruptly loses its elastic properties, though the process is reversible. This is a property it shares with most elastomers. At very cold temperatures rubber is actually rather brittle; it will break into shards when struck or stretched. This critical temperature is the reason that winter tires use a softer version of rubber than normal tires. The failing rubber o-ring seals that contributed to the cause of the Challenger disaster were thought to have cooled below their critical temperature. The disaster happened on an unusually cold day. The glass transition temperature is the temperature below which the physical properties of amorphous materials vary in a manner similar to those of a solid phase (glassy state), and above which amorphous materials behave like liquids (rubbery state). ... Firestone tire A tire (US spelling) or tyre (UK spelling) is a roughly toroidal piece of (usually) rubber placed on a wheel to cushion it. ... Typical O-ring and application An O-ring is a loop of elastomer with a round (o-shaped) cross-section used as a mechanical seal. ... STS-51-L was the 25th launch of a Space Shuttle and the tenth launch of the Challenger. ...

See also

Kuhn length

References

1. ^ ^{a b} Werner Kuhn - Encyclopedia Britannica
2. ^ Kuhn, W. (1934). "Über die Gestalt fadenförmiger Moleküle in Losungen" (On the shape of filform molecules in solutions). Kolloidzeitschrift 68, p. 2.
3. ^ Müller, Ingo (2007). A History of Thermodynamics - the Doctrine of Energy and Entropy. Springer. ISBN 978-3-540-46226-2. 

External links

• Hirsch, Warren (2003). "Disorder in un-stretched rubberbands", JCE, Feb. Vol. 80, No. 2, p. 145