Swollen elastomers

The statistical theory will also describe the response under stress of elastomers swollen by solvents and, in general, it is found that the greater the degree of swelling, the better the agreement between theory and experiment. The modifications necessary for the treatment of swollen networks are relatively straightforward, and the stored energy function becomes... 

Another useful property of LCEs is that their shape changes by applied electric fields, electromechanical responses, owing to reorientation effects induced by electric field. Zentel first found tiny changes of LCEs swollen in LMWLCs under large fields in 1986 (Zentel, 1986). Subsequently, Barnes et al. (1989) observed 20% contraction of polydomain elastomers swollen in an isotropic LMWLC. Kishi et al. 

Yusuf Y, Sumisaki Y, Kai S. 2003. Birefringence measurement of liquid single crystal elastomer swollen with low molecular weight liquid crystal. Chem Phys Lett 382 198 202. 

Yusuf Y, Ono Y, Sumisaki Y, Cladis PE, Brand HR, Finkelmann H, Kai S. 2004b. Swelling dynamics of liquid crystal elastomers swollen with low molecular weight liquid crystals. Phys Rev E 69 021710. 

M. Chambers, R. Verduzco, J.T. Gleeson, S. Sprunt and A. JakU, Calamitic Uquid-crystaUine elastomers swollen in bent-core Uqurd-crystal solvents, Adv. Mater. 21(16), 1622-1626, (2009). doi 10.1002/adma.200802739... 

If values of parameter m of Eq. [10.33] are similar, the viscoelastic properties of elastomers swollen in various Uqtrids are nearly the same (for the system PDUE + DOS, m=7.0 for PDUE + TBP, m=6.6). A srrtaller value of the parameter m corresponds to a smaller change in viscoelastic properties of swollen material. 

Chambers, M. Verduzco, R. Gleeson, J. T. Sprunt, S. Jakli, A. Elexoelectricity of a calamitic liquid crystal elastomer swollen with a bent-core liquid crystal. J. Mater. Chem. 

Chambers M, Verduzco R, Gleeson JT, Sprunt S, Jakli A (2009) Calamitic liquid-crystalline elastomers swollen in bent-core liquid-crystal solvents. Adv Mater 21 1622-1626... 

Strain energy function. In order to solve the hyperelastic problem presented in a later section, it was first necessary to develop a strain energy function for elastomers swollen in solvents. 

Individual liquids and elastomers each possess their own solubility parameter, 5. This is a thermodynamic property which is related to the energy of attraction between molecules. In its simplest form, an elastomer will possess a drive to absorb a liquid of similar 8, and be swollen by it. As the difference between the solubility parameter values of species increases, so their affinity for each other decreases. The commonest units for 8 in the literature are (cal cm ) / to convert values thus to MPa, multiply by 2.05. 

Following this, elastomers can be swollen by some high-pressure gases (especially CO2) as the densities of these gases approach liquid-like levels, at appropriate temperatures they become supercritical fluids which possess a solubility parameter magnitudes that, however, are highly dependent on temperature and pressure... 

Polymers with solubility parameters differing from those of the solvent by at least 2.0 H, will not dissolve in the solvent at room temperature. Thus although unvulcanized natural rubber (NR), unvulcanized styrene-butadiene elastomer (SBR), unvulcanized butyl rubber, and EPDM dissolve in gasoline or benzene, the vulcanized (cross-linked) polymers are swollen but will not dissolve due to the presence of the crosslinks. 

Elastomers are polymeric substances with rubber-like behavior at ambient temperatures. This means they are more or less elastic, extensible, and flexible. They can be exfended by relafively small force and return to the original length (or near it) after the force is removed. Rubber-like behavior can be observed in plastics, but under different conditions, such as at elevated temperatures or in swollen state. These are not true elastomers, however. 

Many studies of vulcanized elastomer blends have revealed discontinuities in physical property trends attributable to poor interfacial bonding. Recently Rehner and Wei (5) have observed discontinuities in the swelling of blended crosslinked networks swollen in a common solvent. This departure from an averaged swelling behavior, based upon compositional ratios and the swelling behavior of the two homophases, re-... 

Adhesion Analysis in Swollen Elastomer Blended Networks... 

Evidence of Interfacial Bonding. In these experiments compounded blends were composed of two elastomer phases that were first mixed with curative ingredients before blending in various ratios. This procedure was adapted to ensure proper initial distribution of the ingredients between the two phases. Blending was accomplished, with one exception, by mill mixing on a small laboratory two-roll mill. After blending, cured specimens in the form of small 0.025-inch thick pads were swollen in a common solvent to observe the over-all state of network... 

Stirring (300 rpm) was started, and the mass was heated and kept at the desired temperature for 2 hours. During this preliminary treatment, the elastomer was swollen and partially dissolved by the monomer. Finally, the remaining water containing the initiator in suspension was introduced, and the reaction was allowed to proceed until the monomer conversion reached the desired value. The polymer, in the form of pearls, was separated from the suspending liquid by centrifugation, washed thoroughly with water, and dried in an oven at reduced pressure. 

Non-ionic polymer gel, swollen with dielectric solvent, can be extremely deformed as is the case for non-ionic polymer plasticised with non-ionic plasticiser. Instead of the charge-injected solvent drag as a mechanism of the gel actuation, the principle is based on local asymmetrical charge distribution at the surface of the gel18. The mechanism can also be applied to non-ionic elastomers in which the motion of the polymer chain is relatively free. In spite of their many difficulties for practical actuators, polyelectrolyte gels and related materials are the most interesting electroactive polymer materials. 

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