University of Connecticut |
Are Polymeric Liquids Solid of Fluid: Examining the Experimental and Theorectical Foundations of Polymer Rheology Friday, October 5, 2007 11:00 am , IMS Room 20 Are polymeric liquids solid or fluid: examining the experimental and theoretical foundations of polymer rheology Shi-Qing Wang, P. Boukany, S. Ravindranath and Y. Wang Department of Polymer Science University of Akron, Akron, Ohio 44325 The presentation will provide an overview of our efforts in a decade to explore the true nature of nonlinear flow behavior of entangled systems including various solutions and polymer melts. Recent experiments based on particle-tracking velocimetric observations have offered new insight into the crucial physics responsible for a variety of familiar phenomena including shear thinning, stress overshoot, and stress relaxation. These results, summarized in Phys. Rev. Lett. 96, 016001; 96, 19601; 97, 187801 (2006) and Macromol. Mater. Engr. 292, 15 (2007), challenge the premise of conventional rheometry (i.e., homogeneous flow) and the established theoretical framework. More importantly, they have urged us to consider new ingredients in a more realistic theoretical description of polymer rheology [J. Chem. Phys. 127, 064903 (2007)]. We found through the intimate interplay between experiment and theory that the elastic entropic force due to chain deformation in flow is principally responsible for generation of inhomogeneous flow by elastic breakup of the entanglement network. This powerful insight has also led to prediction and discovery of two dramatic and unexpected (previously unknown) phenomena: arrested wall slip and breakup of step-stretched filaments made of entangled polymer melts. There are over 20 movies on our website http://www3.uakron.edu/rheology/, showing the experimental findings that have been described or are to be described in our publications (which are also available as pdf files from the same URL).
This seminar is sponsored by a generous grant from U.S. Surgical Corporation |