CHE Seminars  

Speaker Prof. Ravi Prakash Jagadeeshan
Department of Chemical Engineering, Monash University, Australia
Topic Coil-stretch hysteresis in polymer solutions
Date 22,February 2016 (Monday)
Place L-2
4 pm. - 5 pm.

Can a polymer solution have two values of stress at the same value of strain rate? Such a possibility would have significant consequences for many industrial processes that involve polymer solutions, such as ink-jet printing and the spinning of nano-fibres. However, none of the current models for polymer solutions, which are used to solve for the flow of polymer solutions, admits such a possibility. Yet nearly 40 years ago, de Gennes (Nobel prize in Physics, 1991) predicted that polymer solutions could have different states of stress at the same strain rate if their deformation histories were different. It took 30 years for experimental confirmation of de Gennes’ prediction to be achieved by Steve Chu (Nobel prize in Physics, 1997) and Eric Shaqfeh at Stanford, using stained DNA molecules. Until recently, the influence of the concentration of the polymer solution on such hysteretic behavior has been unknown, since de Gennes’ early theory was confined to the limit of dilute solutions. I will show in this talk, through experiments and simulations, that the situation becomes more complicated and intriguing as the polymer concentration increases and as the flow type varies from extensional to shear flow. The phenomenon of hysteresis in polymer solutions provides a fascinating insight into the influence of non-linear effects on the molecular scale on macroscopic solution properties.

Dr. Ravi Prakash Jagadeeshan is currently a Professor in the Department of Chemical Engineering at Monash University, and has been at Monash since January 2001. Before joining Monash, Ravi was an Associate Professor at the Indian Institute of Technology, Madras, and did postdoctoral work on Sandpile dynamics with Prof. S. F. Edwards at Cavendish Laboratory in Cambridge, and on Polymer solution rheology with Prof. H. C. Öttinger at ETH Zürich. He was a Humboldt Fellow in the Techno-Mathematik Department at the University of Kaiserlautern in 1999/2000. Ravi’s research interests revolve around understanding the interaction of flow and micro-structure in complex fluids. Ravi and his students use an array of modelling techniques in their research, including non-equilibrium Brownian Dynamics, closure approximations, and finite element analysis.

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