Structure and dynamics of a poly(dimethylsiloxane) network: a comparative investigation of gel and solution

Abstract

Combined measurements are described involving elastic and quasi-elastic neutron scattering, quasi-elastic light scattering, nuclear magnetic resonance, and swelling pressure on an end-linked poly-(dimethylsiloxane) (PDMS) gel swollen to equilibrium in a good solvent (toluene) and the equivalent solution. The factors affecting the collective diffusion coefficient are considered. The swelling pressure measurements show that the osmotic modulus is appreciably depressed in the gel. The neutron spin-echo measurements reveal no difference in the dynamic response at intermediate and high values of the scattering vector Q. Elastic neutron scattering at small Q detects nonuniformities in the network structure, which are absent from the solution. These nonuniformities play a major role in the dynamic response of the system at lower Q and appear to be the cause of the observed reduction in osmotic pressure. The NMR measurements show a small increase of the solvent mobility in the gel, which is consistent with the appearance of structural nonuniformities in the system.

NMR water self‐diffusion and relaxation studies on sodium polyacrylate solutions and gels in physiologic ionic solutions

“…(2) The cross‐linking process modifies the chemical properties of polymer chains and the polymer–solvent interaction. Our present observation is consistent with evidence from previous macroscopic experiments and theory: there are important thermodynamic differences between the two states, and these changes are not simply proportional to the number of cross‐linking points . Osmotic pressure measurements on poly(vinyl acetate) gel were found to be almost independent of the cross‐linking density of the gel .…”

Scattering properties of poly(vinyl acetate) gels in different solvents

“…For light scattering experiments in polymer solutions, the scattering from concentration fluctuations is usually expressed in terms of the Rayleigh ratios,1° R(0) R(e) = R(~),,,,, -R~~),,,,, = RTWWWW (4) where K (=16*2nz(anlac)2/X4N~) is an optical constant, anlac is the refractive index increment of the polymersolvent system, X is the wavelength of the radiation, and N A is Avogadro's number.…”

Length Scale Dependence of the Dynamic Properties of Hyaluronic Acid Solutions in the Presence of Salt

“…Neutron spin echo (NSE) probes the polymer dynamics in a higher q range [4]. With neutral polymers no difference is detected between D DLS and that measured by NSE, D NSE [5, 6]. In polyelectrolyte solutions, however, where the dynamics of the polymer is coupled to that of the ion cloud, this correspondence remains to be verified experimentally [7].…”