Chemical Engg. Seminar: Prof. Ravi Prakash Jagadeeshan

A mesoscopic model for the rheology of unentangled wormlike micelle solutions

Wormlike micelle solutions are remarkable complex fluids that are currently being used in a wide range of industrial applications. Their property of being ‘living polymer solutions’, which leads to a rich diversity of behaviour, makes the understanding of the connection between their microscopic and macroscopic dynamics a challenge. We introduce the concept of a ‘persistent worm’, representing the smallest possible length of a wormlike micelle, modelled by a bead-spring chain with sticky beads at the ends. Persistent worms are allowed to combine with each other at their sticky ends to form wormlike micelles with a distribution of lengths, and the semiflexibility of a wormlike micelle is captured with a bending potential between springs, both within and across persistent worms that stick to each other. Multi-particle Brownian dynamics simulations of such polydisperse and ‘polyflexible’ wormlike micelles, with hydrodynamic interactions included and coupled with reversible scission/fusion of persistent worms, are used to investigate the static and dynamic properties of wormlike micellar solutions in the dilute and unentangled semidilute concentration regimes. The influence of the sticker energy and persistent worm concentration are examined, and simulations are shown to validate theoretical mean-field predictions. The presence of wormlike micelles that form rings is shown not to affect the static properties of linear wormlike micelles and mean-field predictions of ring length distributions are validated. Linear viscoelastic storage and loss moduli are computed and the unique features in the intermediate frequency regime compared to those of homopolymer solutions are highlighted. Various molecular time scales responsible for these distinctive features are identified. The inclusion of hydrodynamic interactions enables the distinction between Rouse and Zimm dynamics in wormlike micelle solutions to be elucidated, and the concentration beyond which the onset of the screening of hydrodynamic interactions occurs is clearly identified. Insight into the complex interplay between microstructural dynamics and rheological properties of wormlike micelle solutions is obtained, which will prove helpful for the future design and optimization of industrial applications of wormlike micelle solutions.

Biography:

Ravi Prakash Jagadeeshan is currently a Professor in the Department of Chemical & Biological Engineering at Monash University where he has been since 2001. Before joining Monash, he 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 Kaiserslautern in 1999/2000. Ravi’s research interests revolve around understanding the interaction of flow and micro-structure in complex fluids predominantly with the help of nonequilibrium Brownian Dynamics simulations. He is also interested in applying methods of soft matter physics to studying problems in biology. He was elected a Fellow of the American Society of Rheology in 2019 and was awarded the Medallion of the Australian Society of Rheology in 2020.