Speaker: Harishankar Manikantan (Chemical Engineering, UC Santa Barbara)
Title: Nontrivial surface rheology and 2D suspension dynamics of complex fluid interfaces
Surfactant-laden interfaces play central roles in industrial coatings and sprays; drainage, rupture and aging of foams; stabilization or breaking of emulsions; and in the functioning of physiological interfaces like lung alveoli and the tear film, to name a few. However, surfactants themselves generally behave like 'hidden variables' whose presence is inferred from observable fluid phenomena. Surfactants may relax surface stresses by adsorption/desorption from/to the bulk fluid, via 2D phase transitions, through surface rheology that resists flow and deformation within the plane of the interface, or some combination of these processes. I will present theoretical efforts that tease apart effects of physically distinct yet common surfactant transport processes on flow and transport of interfacial systems. I will discuss the impact of discrete condensed domains on apparent surface viscoelasticity, and point to surprising results and their implications in interpreting experimental measurements. I will also analytically explore the strong dependence of surface shear viscosity on the surface concentration of the surfactant, revealing qualitatively new features in paradigmatic and experimentally accessible flows. Ultimately, these problems provide the mathematical framework and the intuitive understanding required for the conceptual design and analysis of complex 2D interfacial materials, which I will motivate by incorporating ideas from classical suspension mechanics into these 2D systems.
Harishankar Manikantan is a postdoctoral researcher in Chemical Engineering at the University of California, Santa Barbara, where he works with Prof. Todd Squires on the dynamics and rheology of complex interfacial materials. He received his PhD in Applied Mechanics at the University of California, San Diego in 2015, working with Prof. David Saintillan on the theoretical and computational modeling of elastic fibers in viscous fluids. Prior to UCSD, he earned a Masters in Theoretical and Applied Mechanics at the University of Illinois at Urbana-Champaign in 2012. Beginning July 2019, he will start as an Assistant Professor of Chemical Engineering at the University of California, Davis.