Start
Dec 22, 2009 - 16:00
End
Dec 22, 2009 - 17:00
Venue
Rm#130
Event Type
Speaker
Dr J Ravi Prakash Monash University
Title
Unfolding of Polymeric Globules in Extensional Flow
The behaviour of collapsed homopolymers and diblock copolymers subjected to extensional flow is examined using fluctuating hydrodynamic simulations. The copolymer blocks are labeled H and P to represent hydrophobic and hydrophilic interactions with the solvent. Collapsed homopolymers are found to undergo a transition in their conformational state from a globular to a stretched state at a critical Weissenberg number. The existence of globule-stretch hysteresis is also demonstrated with the width of the globule-stretch hysteresis window depending significantly on the quality of the solvent. Diblock copolymers are found to exhibit a fascinatingly complex behaviour in extensional flow. With increasing extension rate the P block gets fully stretched while the H block remains coiled. Ultimately a threshold value is reached at which the H block begins to unravel and the copolymer undergoes a coil-stretch transition. The nature of coil-stretch hysteresis in diblock copolymers is found to be significantly different from the hysteretic behaviour of the each of the blocks that make up the diblock. While de Gennes hypothesis for the existence of coil-stretch hysteresis has been experimentally demonstrated for homopolymers there has been no experimental observation so far of the existence or otherwise of coil-stretch hysteresis for diblock copolymers in extensional flow.About the speaker: Prof Ravi Prakash Jagadeeshan is a Reader in Chemical Engineering at Monash University. Before joining Monash Prof Ravi Prakash was an Associate Professor at the Indian Institute of Technology Madras and did postdoctoral work on sand pile 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. His research interests revolve around understanding the interaction of flow and microstructure in complex fluids. His group uses an array of modeling techniques including non-equilibrium Brownian Dynamics closure approximations and finite element analysis. He was the President of the Australian Society of Rheology from 2006 to 2008 and is the current Editor of the Korea Australia Rheology Journal.