Dynamics of a Model for Nematic Liquid Crystalline Polymers in Planar Shear
and Pressure-Driven Channel Flows

D. Harley Klein
Department of Chemical Engineering
UCSB Doctoral Candidate

Date: Monday, February 7, 2006
Time: 4:00 p.m.
Place: Engineering II, Room 3361

ABSTRACT

Liquid crystalline polymers (LCPs) have found a multitude of applications in the form of fibers, and applications that take advantage of the low thermal expansion coefficient and relatively low viscosity of LCPs such as small-scale precision molded parts. In spite of these successes, however, there are other potentially more important applications that have not been realized, among which the greatest loss is the inability to produce high-strength, lightweight engineering materials with mechanical properties that derive from the spontaneous ordering LCPs display in the liquid state. The difficulty lies in the fact that, although the spinning process used to produce fibers enhances this tendency for ordering, other forms of polymer processing, such as injection molding, involve either shear flows or combinations of shear and extensional flows. For LCPs that tumble in shear flows–which include all lyotropic and, apparently, many commercially interesting thermotropic LCPs–these flows seriously degrade or even destroy the orientational order. The question, then, is whether the degradation of orientational order can be controlled sufficiently by some modification of the processing procedure (i.e., modest changes in the flow geometry). A necessary first step is to elucidate the structure-flow interaction and the dependence of the structural evolution on the flow type, and to develop a predictive capability that reproduces experimental observations. Accounting for the coupling between the microscopic structure and macroscopic stress using a molecular-based continuum model, we have analyzed the two- and three-dimensional flows that occur in a linear shear cell and in two-dimensional pressure-driven channel flow. In this talk, I will give an overview of our results, with an emphasis placed upon the strong correlations between our findings and relevant experimental observations reported in the literature.