A MODEL TO DETERMINE LOCAL, MICROSCOPIC FLUX PROFILES WITHIN COMPOSITES FROM THE MEASURED, MACROSCOPIC FLUX - APPLICATION TO POLY(4-VINYLPYRIDINE) COMPOSITES

For any heterogeneous matrix with a parametrizable geometry, a model i s provided to determine a microscopic, local flux profile within the m atrix from the macroscopic, experimentally measured flux of a probe sp ecies. By analyzing the dependence of the measured flux on the geometr ic parameters that describe the matrix, a mathematical function descri bing a local flux profile within the matrix is obtained. Example appli cations of the model include composites of Nafion and neutron track-et ched polycarbonate membranes. Composites of neutron track-etched polyc arbonate membranes and 20% cross-linked poly(4-vinylpyridine) are also described. The measured flux of hydroquinone through the composites v aries with r(0)(-1), where r(0) is the pore radius, a characteristic d imension of the matrix. The measured flux is characterized by a second -order polynomial in r(0)(-1). The local flux profile is found by appl ication of the model and is shown to be higher toward the center of th e pore. Poly(4-vinylpyridine) is cross-linked with various dibromoalka nes, with 2-8 and 12 carbons. A quadratic relationship is found betwee n the measured flux and the chain length of the cross-linking agent, w ith a minimum for 1,6-dibromohexane. Effects of inter- and intrachain cross-linking are discussed.