Rubber elasticity

Résumé

Rubber elasticity refers to a property of crosslinked rubber: it can be stretched by up to a factor of 10 from its original length and, when released, returns very nearly to its original length. This can be repeated many times with no apparent degradation to the rubber. Rubber is a member of a larger class of materials called elastomers and it is difficult to overestimate their economic and technological importance. Elastomers have played a key role in the development of new technologies in the 20th century and make a substantial contribution to the global economy. Rubber elasticity is produced by several complex molecular processes and its explanation requires a knowledge of advanced mathematics, chemistry and statistical physics, particularly the concept of entropy. Entropy may be thought of as a measure of the thermal energy that is stored in a molecule. Common rubbers, such as polybutadiene and polyisoprene (also called natural rubber), are produced by a process called polym

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https://en.wikipedia.org/wiki/Rubber_elasticity

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AFM Force Spectroscopy and Steered Molecular Dynamics Simulation of Protein Contactin 4

Andrzej Kulik, Karolina Anna Mikulska Ruminska

We use a single molecule atomic force spectroscopy combined with the steered molecular dynamics simulation to determine a mechanical behavior of neural cell adhesion protein contactin during its unfolding. Force curves typical for modular proteins were observed, showing at most four unfolding peaks. The analysis of force spectra performed within worm-like chain model of polymer elasticity showed the presence of three unfolding lengths. Small plateaus, most likely resulting from forced transitions within domains were observed for the first time. Steered molecular dynamics simulations help to determine atomistic picture of domain unfolding.

Polish Academy of Sciences Warsaw2009

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A MLS-based lattice spring model is presented for numerical modeling of elasticity of materials. In the model, shear springs between particles are introduced in addition to normal springs. However, the unknowns contain only particle displacements but no particle rotations. The novelty of the model lies in that the deformations of shear springs are computed by using the local strain obtained by the moving least squares (MLS) approximation rather than using the particle displacements directly. By doing so, the proposed lattice spring model can represent the diversity of Poisson's ratio without violating the requirement of rotational invariance. Relationships between micro spring parameters and macro material constants are derived from the Cauchy-born rules and the hyperelastic theory. Numerical examples show that the proposed model is able to reproduce elastic solutions obtained by finite element methods for problems without fractures. Therefore, it is capable of simulating solid materials which are initially continuous, but eventually fracture when critical stress and/or displacement levels are reached. A demonstrating example is presented.

World Scientific Publ Co Pte Ltd2012

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On the influence of "arm-on, arm-off" processes on alkene hydrogenation catalysed by a rhodium triphos complex

Paul Joseph Dyson

The influence of phosphane "arm-on, arm-off" assocn./dissocn. in rhodium catalyzed alkene hydrogenation using [Rh(COD)(k3-triphos)]PF6 {1, COD = cyclooctadiene, triphos = 1,1,1-tris(diphenylphosphanylmethyl)ethane} has been investigated by comparison of the activity of 1 to mixts. of the related diphosphane complex, [Rh(COD)(k2-dppp)]PF6 {2, dppp = 1,3-bis(diphenylphosphanyl)propane} and triphenylphosphane (THF, 50 °C, 1 bar H2). These investigations are supplemented by a demonstration of the k2-k3 fluxionally of the triphos coordination in 1 by reversible reaction with [RuCl2(p-cymene)]2 at room temp. in CH2Cl2. The product of this reaction, the bimetallic complex [(p-cymene)Cl2Ru{(PPh2CH2)CMe(CH2PPh2) 2}Rh(COD)]PF6, was isolated and fully characterized, including detn. of the solid-state structure by X-ray diffraction anal. Despite this evidence for facile arm-off dissocn. of the triphos ligand in 1, complex 2, with or without triphenylphosphane, was found to be more efficient for the hydrogenation of styrene and cyclohexene. Notably, use of triphenylphosphane together with 2 was found to have beneficial effects - increasing the rate of styrene hydrogenation (in some cases) and helping to stabilize the metal center during cyclohexene hydrogenation. These observations are supported by mercury poisoning expts. and reactivity expts. with 2 in medium pressure sapphire NMR tubes.

2007

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