Solvent diffusion in a gel when escaping the confining polymer cage

Abstract.

The diffusive motions of propylene carbonate contained in a deuterated poly(methyl methacrylate) gel is investigated using quasi-elastic neutron scattering. The solvent motion is probed at length-scales up to the typical distance between chains in order to characterize the dynamics of the solvent escaping its confining polymer `cage'. The experimental data are well described by a model based on a combination of free and spatially restricted diffusion corresponding to the partial or temporary entrapment of the solvent in the polymer cages. The extracted confinement length of the restricted diffusion compares well with the polymer–polymer distance obtained from small angle neutron scattering data. By comparing with pulsed field gradient NMR and dielectric spectroscopy data we show that over the whole temperature range from the slow relaxations at the glass transition to long range diffusion the solvent dynamics is systematically slower in polymer gels than in bulk solvent.