Journal of Physical Chemistry B, Vol.108, No.3, 1137-1142, 2004
Carrier diffusivity in porous membranes
Carrier diffusivity of a lithium electrolyte solution in porous membranes was evaluated by observation of diffusion behavior of ionic species using NMR spectroscopy. We performed analysis on the basis of the restricted diffusion model and a new idea of diffusion distribution. That new concept is engendered in the assumption that observed diffusion values are distributed according to pore size distribution and nonuniformity of pore,and polymer density in a membrane. Carrier diffusivity in polyethylene (PE) porous membranes showed characteristic echo attenuation, which differs from echo behavior as a result of random walk migration. We first tried to simulate the echo change on the basis of the restricted diffusion model in porous structure, resulting in disagreement with the observed echo change. As a result, the idea that diffusion values are distributed concurrent with porous geometry was applied to interpret the situation. Introduction of a Gaussian function to represent the distributed condition yielded highly reproducible results for the membranes. Carrier diffusivity in porous PVDF membranes showed a narrow distribution compared with that of PE membrane. The swelling feature of the PVDF polymer would contribute to averaging the pore size and preparing the uniform network for carrier transport pathway.