The talk will focus on developing and utilizing different computer simulation techniques and theoretical methods to understand the fundamental physics of polymers relevant to pharmaceutical, food and manufacturing industries. The first part of the talk will focus on using coarse-grained molecular dynamics simulations to elucidate the role of charge sequence on the adsorption of polyelectrolyte solution on to oppositely charged polyelectrolyte brush. To this end, we consider four different model systems wherein the free and the brush polyelectrolytes can have either block or alternating charge sequences. Our model treats the polyelectrolytes in a bath of implicit solvent, explicit counterions and excess salt. Adsorption efficiency is highest when both free and brush polyelectrolytes possess a block charge sequence, and it is lowest when both free and brush polyelectrolytes possess an alternating charge sequence. By computing the free energy, internal energy and entropy of adsorption using umbrella sampling methods, we find that the origin of the differences in adsorption efficiency for different charge sequences is enthalpic. Additionally, equilibrium conformations for different charge sequences reinforce the results obtained from energetic calculations. This work can guide the design of layer-by-layer deposition of thin films and can help in understanding transport across cell membranes in the presence of naturally occurring intrinsically disordered proteins.
The second part of the talk will focus on the self-assembly of methylcellulose in solution. Methylcellulose (MC) is a biopolymer obtained from cellulose and widely used in the food and drug industries. Aqueous MC solutions undergo lower critical solution temperature behavior and form stable hydrogels at high temperatures. Recent experiments on dilute aqueous MC solution show a clear fibrillar morphology upon heating. However, the physics of the origins of such formation is poorly understood. To this end, we performed coarse-grained molecular dynamics simulations to understand the mechanisms involved in the fibril formation of methylcellulose. Explicitly, we look at the different precursor steps that are involved in the MC fibrillar formation. We showed that the current theories of stacked toroid model for fibril formation is valid only at certain polymer concentrations. Rather, we showed the existence of a nucleation mechanism and the importance of conformational fluctuations for systems containing randomly coiled chains. Understanding this physical phenomenon is essential to controlling the strength and flow properties of the aggregate formed.
Dr. Vaidyanathan graduated from National Institute of Technology, Calicut, India in 2010 with Bachelor of Technology in Chemical Engineering. Following his undergraduate studies, he completed M.Sc. (Engg) in Chemical Engineering from Indian Institute of Science, Bangalore in 2012 under the guidance of Prof. K. Ganapathy Ayappa, and Ph. D. in Chemical Engineering from University of Texas at Austin in 2017 under the guidance of Prof. Venkat Ganesan. His Ph.D. work focused on multi-scale simulations of microphase-segregated block copolymers for battery applications. Currently, he is a postdoctoral research fellow with Prof. Kevin D. Dorfman at University of Minnesota. His current research focuses on understanding self-assembly mechanisms of methylcellulose systems, and polyelectrolyte systems using
coarse-grained molecular dynamics simulations.