Glassy Polymers are being increasingly used in the construction and fabrication of high-tech 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 polymer network. To examine the behavior of such systems both on the macroscopic and molecular level, it is important to study the penetrant diffusion process. In such transport, the macromolecular chains rearrange toward 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 diffusion 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. We have developed a new method that can be applied on dry and slowly swelling discs and can be used to identify the swelling and the dissolution process. The swelling behavior was investigated using high-resolution X-ray computed tomography. This is a completely nondestructive technique and can be used to visualize features in the interior of opaque solid objects, and to obtain digital information on their 3-D structure and properties. We have obtained real and computerized profiles of discs swollen/dissolving in various penetrants/solvents. We followed the gel layer dynamics and determined density variation in swellable discs. The surface area and volume of the samples were measured with appropriate software. The use of nondestructive high-resolution X-ray computed tomography can be effectively applied to study the progressive expansion and dissolution of swellable systems.

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