Multiaxial deformations of end-linked poly(dimethylsiloxane) networks. 4. Further assessment of the slip-link model for chain-entanglement effect on rubber elasticity

摘要

The Edwards-Vilgis slip-link model for the chain-entanglement effect on rubber elasticity is critically assessed on the basis of quasiequilibrium biaxial stress-strain data of end-linked polydimethylsiloxane (PDMS) networks with different entanglement densities. The PDMS networks with different entanglement densities were prepared by end-linking end-reactive long precursor PDMS in solutions with different solvent contents. The slip-link model, in which trapped entanglement is modeled by fictitious mobile slip-link attaching two entangled chains, satisfactorily describes the biaxial data over the entire range of deformation for all the networks examined. The model-specific parameters, i.e., slippage of slip-link (eta) and inextensibility of network (alpha), were employed as adjustable parameters in data-fitting. The fitted values of eta and alpha vary reasonably with the degree of dilution at network preparation, i.e., entanglement density. With an increase in dilution, i.e., decrease in entanglement density, eta increases, whereas alpha decreases. In addition, the fitted values of eta and alpha are in good agreement with the estimates from another molecular approach independent of mechanical testings: eta=M_e/M_c, where M_e and M_c are the molecular masses between neighboring entanglements and between adjacent cross-links, respectively; alpha=n_j~(-1/2), where n_j is the number of Kuhn segments between adjacent elastically effective junctions including cross-links and trapped entanglements. The satisfactory data-fit with the model parameters of physically reasonable magnitudes supports the validity of the slip-link model for entanglement effects on rubber elasticity.