General

The properties of polymeric materials are often determined by their structure, especially at the nanometer and micron length scales. These microstructural features, in turn, are influenced by the engineering processes which formed the polymers, e.g., reaction, thermal history, shaping, and stretching. Our research interests in advanced materials focus primarily on the relationship between processing and structure in polymeric materials and composites.

Electrorheological Fluids

Electrorheological (ER) fluids are smart materials whose viscosity and stiffness can be quickly varied from liquid-like to solid-like with the application of an electric field. They are receiving extensive consideration for hydraulic devices such as valves and clutches, and for vibration damping devices such as shock absorbers.

Our research investigates the potential use of liquid crystalline polymers (LCPs) as ER fluids, especially on microfluidic applications. LCPs are elongated, rigid molecules, which adopt a distribution of molecular orientations at rest, as seen in the accompanying micrograph. However, when subjected to a strong orienting field, such as an extensional flow field or an electric field, the polymer molecules cooperatively align nearly parallel to each other. The direction of orientation can be controlled by the competing effects of flow field and electric field, with a material response time on the order of milliseconds.

We are examining the ER effect in LCP solutions through a research effort that includes molecular design and synthesis of new polymers, experimental measurement of flow properties, and theoretical modeling of electrical and rheological behavior. In particular we have applied molecular theories to describe LCP ER behavior, so that we can directly determine the influence of molecular-level properties on the rheological behavior of LCP solutions. This is of tremendous benefit to ER device designers, who can design both the equipment and the fluid to meet required specifications.

Polymer Processing with Supercritical Fluids

Supercritical fluids (SCFs) can combine the density and solvent quality of a liquid with the viscosity and transport properties of a gas, so they offer attractive features as potential solvents in various polymer processes. In many of these processes, both polymer solution thermodynamics and transport phenomena (fluid mechanics, mass and heat transfer) influence the structure and properties. Our research focuses on SCF processes for producing fine particles for controlled release drug delivery.In these processes, biodegradable polymers are coprecipitated with therapeutic agents such as live viruses directly into solid particles by lowering the pressure of a carbon dioxide-swollen polymer. Through experiments and modeling, we seek to describe the effect of material, design and operating parameters on the size, shape and structure of the drug delivery particles.