Dr. Koelling has research interests in the processing and rheology of polymer melts and solutions. 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 techniques including fiber spinning, blow molding, and injection molding, and in a variety of phenomena including turbulent drag reduction, jet stability, and anti-misting. Two rheometers based on techniques of fiber spinning and filament stretching have been developed in our lab to measure the extensional viscosities of complex fluids. Using this rheometer the following important questions will be addressed. Are extensional flow properties the additional information needed to characterize the behavior of viscoelastic fluids? Do existing constitutive equations properly describe both shear and shear-free material functions of viscoelastic fluids.
Dr. Koelling is also studying a novel polymer processing technique called gas-assisted injection molding. This process involves the partial injection of polymer melt into a mold cavity, followed by injection of high pressure gas. The gas penetrates through the viscous polymer melt and hollows out the interior of the mold. This process is capable of producing light-weight, rigid 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.
Dr. Koelling is also interested in the processing of liquid crystalline polymer (LCP) systems. The development of ultra-high modulus and tensile strength Kevlar fibers by Dupont in the 1970s has focused the attention of polymer scientists and engineers on new process technologies for LCP's. Areas of research that are important to the potential development of new commercial LCP products include rheological and rheoptical investigations and studies of structure development as a function of processing conditions in different fabrication operations.
Potential Thesis Topics
- Measuring the molecular orientation of polymer molecules in an extensional flow using birefringence techniques.
- Developing an extensional rheometer and studying the extensional rheology of monodisperse polymers.
- Extensional rheology of dilute and semi-dilute polymer solutions.
- Gas assisted injection molding of polymer melts.
- Dynamics of gas bubble penetration through viscoelastic fluids.
- Process/structure/property relationships for thermoplastic composite materials.
A Rheological Testing Center is available for studying the rheology and structure of polymer melts and solutions as well as mechanical properties of thermoplastics and composite materials. This center is well-equipped with a Rheometrics Mechanical Spectrometer (RMS-800), Rheometrics Fluids Spectrometer (RFSII), Rheometrics Solids Analyzer (RSAII), and a Rheometrics Extensional Analyzer (RFX). A Cincinnati Milacron injection molding machine with a Cinpress gas unit is available to study the gas-assisted injection molding process. Two extensional rheometers based on techniques of fiber spinning and filament stretching have been developed in Dr KoellingÕs lab to study the extensional rheology of viscoelastic fluids. A UV-visible spectrophotometer equipped with a flow cell is available to measure drug release kinetics from controlled drug release devices. Other equipment available includes a Dynamic Light Scattering Apparatus, a Waters Gel Permeation Chromatograph, Polarizing/Phase Contrast Microscope, and X-ray diffractometer.