In recent years, glassy polymers have become important materials for construction of micro- and nano-devices. These devices are often used in applications, such as microfluidics, membranes, artificial tissues, bones, and organs, and controlled drug delivery, where the polymers come into contact with fluids capable of penetrating the glassy polymeric networks. In such transport processes, the macromolecular chains rearrange towards new conformations, where the rate of relaxation depends on the penetrant concentration. The relative rates of penetrant diffusion and macromolecular chain relaxation determine the nature of the transport process and lead to a wide variety of penetrant transport phenomena, such as Fickian, Case II, and anomalous (non-Fickian) sorption behavior.

Fickian transport models are useful in their relatively easy solution by analytical or numerical methods. The adjustable material properties are generally determined by fitting the experimental data to the model. Non-Fickian transport processes have often been described by modified Fickian models utilizing a convective term in the penetrant flux; changes in the polymer morphology resulting in a variable penetrant diffusion coefficient; and non-Fickian propagation of a swelling front. In order to better understand the interplay of diffusion and relaxation phenomena that governs the transport behavior of polymer-penetrant systems, we have developed a technique that can be applied to dry and slowly swelling materials. High-resolution x-ray computed tomography, a completely nondestructive technique that can be used to visualize features in the interior of opaque solids, has been successfully adapted to examine the dynamics of the transport of methanol into glassy poly(methyl methacrylate).

Work supported by a grant from the National Science Foundation (CTS-0329317) and a Fellowship from the Department of Defense to AKE.