Relaxation Dynamics of Multiarm Polymer Liquids

Cornell University, Ithaca NY

Investigators

Abstract

Experimental studies of stress relaxation dynamics of well-defined branched polymer liquids have long been recognized as important for understanding structure-processing relationships in commercial long-chain branched polyolefins. When these studies are performed using well-characterized entangled branched polymers they can provide direct insight into more general relationships between molecular architecture, relaxation dynamics, and rheology. The objective of the proposed research is three-fold. First, to determine the effect of branch point motion and constraint release on the linear rheology of model branched polymers. Second, to advance fundamental understanding of nonlinear rheology of entangled branched polymer liquids in shear and extensional flow. Finally, to devise methods for visualizing motion and stress relaxation processes in branched polymer liquids. Benefits of the proposed research extend beyond its direct impact on scientific understanding of branched polymer dynamics. The research, for example, addresses a problem of considerable industrial importance at a time when advances in metallocene catalyst chemistry are allowing unprecedented control of molecular architecture in commercial branched polymers. Fundamental understanding of structure-processing relationships in these materials will help reduce expensive trial-and-error experimentation now required to optimize existing processes for new materials. The proposed research also comes at a time when the first rigorous treatments of architecture effects on polymer processing and properties are beginning to appear in textbooks. This research will impact education in a variety of ways. Knowledge developed by study will improve the quality and scope of information about branched polymer physics written in text books and taught in the classroom. The proposed fluorescence microscopy experiments using branched DNA will also provide an excellent demonstration tool for modern courses in polymer science. Finally, the graduate and undergraduate student researchers who will work on the project will receive training in several emerging areas of polymer science and engineering.