To model a polymer gel or an elastomer undergoing a large change in volume under the action of a solvent diffusing in or out of it, a theoretical approach based on an elastohydrodynamic point of view is proposed. Drawing a parallel between the polymer network/solvent system of interest and a liquid flowing through a porous medium, the friction between the polymer and the solvent is described phenomenologically. An equation that couples the large elastic deformations undergone by the polymer network and the diffusion process is derived and then solved numerically in various cases. Special emphasis is placed on the influence of the shear elasticity during the diffusion process. During the swelling process, a nonzero shear modulus induces a nonisotropic swelling at the surface that is responsible for the “sigmoidal” shape of the mass uptake of solvent with the square root of time, as well as for the presence of a “front” in the concentration profile when the solvent advances inside the network. In a permeation process, the solvent flux deviates from its linear behavior as soon as a nonnegligible deformation of the membrane is present. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 166–182, 2003

Some poly(vinylidene fluoride) (PVdF) microporous separators for lithiumion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF 6 , were characterized by the study of the swelling phenomena on dense PVdF membranes. We were interested in the evolution of the swelling ratios with respect to different parameters, such as the temperature, swelling solution composition, and salt concentration. To understand PVdF behavior in microporous membranes and, therefore, to have a means of predicting its behavior with different solvent mixtures, we correlated the swelling ratios in pure solvents and in solvent mixtures to the solvent-polymer interaction parameters and solvent-solvent interaction parameters. We attempted a parametric identification of swelling curves with a very simple Flory-Huggins model with relative success.

We investigate here the stability of a gel cylinder subject to a strong surface tension. Both the criteria for the occurrence of a peristaltic instability and its dynamical evolution are determined within linear elasticity. Shrinking gels may show such an instability, as has been reported by Matsuo and Tanaka [Nature 358, 482 (1992)]. Considering approximate values of the relevant parameters, we find results in qualitative agreement with their experiments.

Some microporous poly(vinylidene fluoride) (PVdF) separators for lithiumion batteries, used in liquid organic electrolytes based on a mixture of carbonate solvents and lithium salt LiPF 6 , were characterized by the study of the swelling phenomena on dense PVdF membranes. Various aspects of the kinetics of the carbonate solvents and the solvent mixture sorption in dense PVdF slabs were studied at different temperatures. Non-Fickian behavior, characterized by S-shaped sorption curves, was highlighted, and a salt effect, which resulted in two-stage sorption, was studied. Diffusion coefficients and activation energies were calculated for the Fickian portions of the sorption curves, that is, at short times and low swelling ratios. A strong influence of the different interaction parameters was shown for the swelling kinetics. This study proved that the swelling of microporous PVdF membranes could be considered instantaneous.