My current research interests are in the rheology and processing of complex fluids, including polymer melts and solutions as well as carbon nanotube and nanoplate polymer composites. One of the most difficult challenges in rheometry is the measurement of extensional viscosities. This material property is of fundamental importance in many polymer processing operations, including fiber spinning, blow molding, and injection molding, and in a variety of phenomena including turbulent drag reduction, jet stability, and anti-misting. Four extensional rheometers based on techniques of fiber spinning, stagnation point flow, contraction flow, and filament stretching have been developed in our lab to measure the extensional viscosities of complex fluids. Using these rheometers we are addressing the following important questions. Are extensional flow properties the additional information needed to characterize the behavior of viscoelastic fluids? Can existing constitutive equations properly describe both shear and extensional material functions of viscoelastic fluids? 

My research group is also studying the dynamics of gas bubble penetration through viscous and viscoelastic fluids. This problem has practical applications in gas-assisted injection molding, enhanced oil recovery, thermoset composite 

This process is capable of producing lightweight, rigid plastic parts with improved surface quality. The effects of processing conditions and polymer rheology on gas penetration through the molded part are being investigated. Fundamental free surface flow studies are also being conducted to determine how bubble dynamics are influenced by viscoelasticity and non-isothermal flow behavior. Computational fluid dynamics are being used in conjunction with experimental studies to determine the important physics required to determine bubble shape and hydrodynamic coating thickness. 

Other areas under investigation include transport problems involving void formation and removal in thermoset composite processing, thin-wall injection molding, microcellular foam processing, polymer nanocomposites, microfluidic devices, and development of biocompatible polymers.