Solvent swelling, determination

The description of the physical properties of fluoroelastomers is necessarily less precise than that of fluoroplastics because of the major effect of adding curatives and fillers to achieve useful cross-linked materials of a given hardness and specific mechanical properties Generally, two parameters are varied increasing cross-link density increases modulus and decreases elongation, and raising filler levels increases hardness and decreases solvent swell because of the decreased volume fraction of the elastomer In addition to these two major vanables, the major determinants of vulcanizate behavior are the chemical and thermal stabilities of its cross-links The selection of elastomer, of course, places limits on the overall resistance to fluids and chemicals and on its service temperature range... 

The typical dependence of the swelling ratio a on the solvent quality determined by the parameter x, which is proportional to the second virial coefficient B, is shown in Figure 3. The coil-globule transition proceeds as a first-order phase transition with a jump in the size somewhat below the 6-point ... 

Padden (1964) have employed the freezing point depression of solvent-swelled NR-BR blends to determine the crosslink densities of the individual polymer phases. The freezing point depression of a solvent in a swollen vulcanizate is dependent on the volume fraction of solvent in the elastomer phase. 

Hydrogels experience recoverable elasticity if the applied strain is modest (<20% in most instances). Since gel networks are often amorphous and homogeneous, strain recovery is expected whether stresses are isotropic, anisotropic, or bulk, as in the case of solvent swelling. Therefore, mbber elastic theory can be used to determine critical hydrogel parameters, originally developed for vulcanized mbber, and later modified for polymers. Further modifications for gels... 

In most cases, stability and oxidation potential issues mean that polythiophenes are prepared, studied, and used in non-aqueous media, and the influence of the solvent can be significant. The extent of solvent swelling is determined by polymer-solvent interactions, which can be manipulated both by choice of solvent and introduction of substituents, here in the 3- and 4-positions. Electropolymerization of alkyl-substituted thiophenes provides good examples of the effects one can observe. EQCM (with PBD) measurements of potentiodynamic deposition from acetonitrile benzonitrile (4 1) of poly(didodecylterthiophene) (with the substituents in the 3, 4 - or 3,3"-positions) showed that film deposition occurred primarily during the reductive half-cycle, in the form of short chain oligomers of the... 

In the last decades of evaluation of the physical network density of SPU was done on samples swollen to equilibrium in two solvents. Swelling of SPU in toluene practically does not affect hard domains. Swelling of SPU (based on oligoethers diol) in a tributyl phosphate (a strong acceptor of protons) results in full destruction of the physical network with hard domains. The effective network density was evaluated for samples swollen to equilibrium in toluene according to the Cluff-Gladding method. Samples were swollen to equilibrium in TBP and the density of the physical network was determined from equar tion ... 

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