Failure in extensional flow of entangled polymer melts

Cuny City College, New York NY

Investigators

Abstract

ABSTRACT PROPOSAL NO.: CTS-0625072 PRINCIPAL INVESTIGATOR: MORTON DENN INSTITUTION: CUNY CITY COLLEGE FAILURE IN EXTENSIONAL FLOW OF ENTANGLED POLYMER MELTS This grant supports a study focused on the failure of polymer melts in extensional flows using a stochastic model for entangled polymer liquids. Modeling results will be compared to experimental data for strain at failure and recoverable strain with the goal of understanding this phenomenon at a coarse-grained molecular level. The PI has recently developed a consistent stochastic tube model of entangled chains in shear flow. The model accurately predicts the steady shear rheology of entangled narrow-distribution linear polymers without adjustable parameters, and it predicts the transient shear rheology with a single adjustable parameter that defines the time scale. The stochastic model has been adapted to study flow of an entangled polymer near a wall that is covered with tethered chains; the model successfully predicts wall slip velocities and slip lengths in shear flow within the range observed experimentally, where the observed increase in slip with increasing shear rate is a consequence of a decrease in the entanglement density near the wall. Under this grant the stochastic model will be adapted to extensional flows in order to study high-rate extensional flow and recovery of entangled polymeric liquids, and to explore the consequences of extension at high rates on the entanglement density and possible failure mechanisms in polymer melts. The proposed research addresses a critical problem in polymer processing, with the potential to have a major impact on industrial practice. The research group is a part of the interdisciplinary Benjamin Levich Institute for Physico-Chemical Hydrodynamics and the NSF-CREST Center for Mesoscopic Modeling and Simulation, and there is considerable interaction among the faculty and students, from the Departments of Chemical, Biomedical, and Mechanical Engineering, Chemistry, and Physics. There will also be regular joint seminars and new soft materials courses developed as part of an NSF-IGERT program on Multiscale Phenomena in Soft Materials. City College is an urban institution with an 85% minority student body overall and a 50% minority student body in the School of Engineering that includes many returning students, often with family responsibilities. Two undergraduates, who wish to pursue undergraduate independent research or summer research, will be recruited into research group annually. The PI will benefit from the presence on the campus of many programs already in operation to enhance the participation of members of groups underrepresented in science and engineering, including the CUNY Pipeline Program for undergraduates interested in pursuing a Ph.D. program.