Deformation and dynamics of droplets with complex interfaces – a study of vesicles, cells, and droplets in biology

Abstract: Droplets with viscous and/or elastic interfaces are found in many applications in industry and biology – for example, cells and vesicles in biology, capsules in drug delivery, Pickering emulsions in consumer products, and protein-adsorbed droplets in foods. Despite their common occurrence, there are still many open questions as to how complex interfaces due to adsorbed lipids, proteins, polymers, or solid particles alter droplet dynamics like sedimentation, breakup and coalescence. This talk will discuss some of our recent work in this area of science. The first part of the talk will discuss our studies on giant unilamellar vesicles (GUVs) -- i.e., sacs of fluid of ~20 microns enveloped in a phospholipid bilayer. We perform microfluidic experiments and boundary element simulations to probe their stretching behavior under steady and time-dependent extensional flows, and characterize the conditions under which they become mechanically unstable and form thin threads. We also discuss future work in understanding how such external flows may alter the thermodynamics and kinetics of lipid phase behavior on biological cell membranes. In the second half of the talk, we discuss more general problems about how surface shear and dilatational rheology of surfactants alter droplet dynamics. In particular, there are several classes of surfactants (e.g., lipids, proteins, and solid particles) whose adsorbed layer are found to exhibit surface viscosity for both shear and dilatational deformations. We perform boundary element simulations of droplets with a viscous interface, and determine how surface viscosity alters three classic problems in droplet dynamics: (a) the formation of a thin threads or cavities during sedimentation, (b) breakup in extensional flow, and (c) drainage during the initial stages of coalescence. For all three cases, we discuss how surface rheology gives rise to qualitatively different droplet dynamics than if Marangoni effects (i.e., gradients in surface tension) were present. We also discuss how droplets behave when both effects are present simultaneously.

Bio: Dr. Vivek Narsimhan is the Michael and Carolyn Ott Assistant Professor of Chemical Engineering at Purdue University.  His research uses theory, simulations, and experiments to examine problems in the areas of suspensions, complex interfaces, fluid mechanics, and polymers. His lab develops mathematical models, simulations, and experiments to describe the mechanics of droplets, red blood cells, and vesicles under various flows and microfluidic geometries. His lab also examines the mechanics of suspensions, characterizing the motion of particulates in polymeric fluids and the rheology of starches.  Other areas of research include fundamental studies in transport phenomena such as mathematics of diffusion and heat/mass transfer in biomedical devices (dialysis) and pharmaceuticals (lyophilization).

Prior to joining Purdue, Dr. Narsimhan obtained a B.S. in Chemical Engineering from Caltech and a Master in Advanced Study in Mathematics from the University of Cambridge under a Churchill Scholarship. He received his Ph.D. at Stanford in the Department of Chemical Engineering under the supervision of Prof. Eric Shaqfeh, where he performed research on problems related to droplets and biological fluid mechanics.  He performed his postdoctoral work with Prof. Patrick Doyle at MIT, where he modeled the dynamics of self-entangled (knotted) polymers.  While at Purdue, he leads a team of five PhD students and one postdoc in the areas of fluid mechanics and transport phenomena.  He has been awarded a Doctoral New Investigator Award from the ACS Petroleum Research Fund, and has won the Philip C. Wankat Graduate Teaching Award from Purdue’s Davidson School of Chemical Engineering.

All seminars are held on Wednesdays from 12:00 noon-1:00 p.m. in the Bowen Hall Auditorium Room 222. A light lunch is provided at 11:30 a.m. in the Bowen Hall Atrium immediately prior to the seminar.