Model poly(dimethylsiloxane) (PDMS) networks and imperfect networks containing pendant chains and branched structures are prepared by end-linking mixtures of di-and monofunctional PDMS and a tetrafunctional cross-linker. Values of the equilibrium modulus of the networks, obtained from dynamic mechanical experiments, illustrate the importance of the entanglement contribution to the elastic modulus. The extents of equilibrium swelling are determined for the networks in two solvents, toluene and benzene. The predictions from the c* theorem do not apply to the model networks due to extensive interspersion of the network chains, which leads to entanglements that are not removed by swelling. The Flory-Rehner model, coupled with the phantom network model gives good agreement with swelling results when the experimentally measured elastic modulus is used in the analysis.

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In this work we present an improved approach for the analysis of (1)H double-quantum nuclear magnetic resonance build-up data, mainly for the determination of residual dipolar coupling constants and distributions thereof in polymer gels and elastomers, yielding information on crosslink density and potential spatial inhomogeneities. We introduce a new generic build-up function, for use as component fitting function in linear superpositions, or as kernel function in fast Tikhonov regularization (ftikreg). As opposed to the previously used inverted Gaussian build-up function based on a second-moment approximation, this method yields faithful coupling constant distributions, as limitations on the fitting limit are now lifted. A robust method for the proper estimation of the error parameter used for the regularization is established, and the approach is demonstrated for different inhomogeneous elastomers with coupling constant distributions.

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The orientations of fibres in a semi-dilute, index-of-refraction-matched suspension in a Newtonian fluid were observed in a cylindrical Couette device. Even at the highest concentration (nL3 = 45), the particles rotated around the vorticity axis, spending most of their time nearly aligned in the flow direction as they would do in a Jeffery orbit. The measured orbit-constant distributions were quite different from the dilute orbit-constant distributions measured by Anczurowski & Mason (1967b) and were described well by an anisotropic, weak rotary diffusion. The measured ϕ-distributions were found to be similar to Jeffery's solution. Here, ϕ is the meridian angle in the flow-gradient plane. The shear viscosities measured by Bibbo (1987) compared well with the values predicted by Shaqfeh & Fredrickson's theory (1990) using moments of the orientation distribution measured here.

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The effect of entanglements on deformation properties of end-linked networks was investigated using Monte Carlo simulations. Model tetrafunctional networks were prepared by crosslinking precursor monodisperse chains in the framework of the bond fluctuation model (BFM). The degree of entanglement in these networks was tuned by changing the precursor chain lengths (N ) 20 and 50-mers) and the initial polymer concentration (Φ 0). Continuum-space simulations of isotropic swelling and uniaxial deformation were carried out in isobaric and isostress ensembles, respectively. Both equilibrium swelling and force-strain data indicated that elastic forces are enhanced in more entangled networks. The effect of Φ0 on the equilibrium swelling and on the elastic modulus was analyzed with the help of scaling theory and the Rubinstein and Panyukov model, respectively; our results are shown to be consistent with reported experimental data. Our results indicate that the effect of entanglements on the network elastic response is the largest at small extension and decreases with strain at higher extensions (supporting an entanglement-slippage scenario).