Experimental and Theoretical Studies of Polymeric Liquids in Extension-Dominated Fluids

9700034 Leal The ultimate objective of this GOALI award (supported jointly by the Division of Materials Research and the Office of Multidisciplinary Activities) is the development of a predictive basis to describe the behavior of solutions of linear-chain, flexible polymers in flows that are either extensional or extension-dominated. The primary emphasis is on solutions that are sufficiently ent angled that reptation-based theories are expected to apply. The proposed experimental studies utilize a novel combination of flow cells, known as 2- and 4- roll mills, that are designed to produce pure extensional, or extension-dominated, two-dimensional flows, that can also be either steady, or time-dependent; and optical techniques that can probe the chain configuration and the actual velocity gradient at any point within the flow cell. Chain configuration is inferred from two-color birefringence measurements of the degree of optical anisotropy in the fluid. A unique implementation of dynamic light scattering provides a pointwise measure of the velocity gradient for either steady or transient flows. Comparisons with theoretical models are made via full-field fluid dynamics simulations for the dilute, Boger-type fluids. For reptation-based models of monodisperse and bi-disperse entangled solutions, measured biorefringence data is compared with model predictions using the measured velocity gradient data as input. %%%% From a technological point of view, the ability to predict the behavior of polymeric liquids in extensional flows would allow an understanding of the relationship between material characteristics and processing. From an educational standpoint, this GOALI project offers enhancements to the normal Ph.D. program. Graduate students will spend up to a year in residence at the Exxon Corporate Research Laboratory, where they will work directly with Scott Milner, as well as visiting the Exxon Research Labs at Baytown where work is being carried out on both polymer synthesis and polymer processing issues that are directly related to the fundamental objectives of this project. ***