"Microrheology at interfaces: Brownian motion in 2D"

Dr.  Vikram Prasad

Abstract

“Soft” matter consists of materials with both elastic and viscous properties; some well known examples include toothpaste, shaving creams/gels and mayonnaise.  However, less is understood about 2D soft systems such as soap films. A key parameter in such systems is the surface viscosity, which is the determining factor for many diverse physical processes such as diffusion of lipid rafts on the cell membrane, draining of soap films, or the behavior of lung surfactants in the alveoli. Therefore, accurate measurements of the surface viscosity are crucial to the understanding of 2D phenomena. We use the thermal motion of tracer particles to determine the surface viscosity of two model interfacial systems: protein (albumin) molecules at an air-water interface and soap films. We developed a technique that measures the correlated thermal motion of pairs of tracer particles at interfaces, and relates this to the surface viscosity. Our method overcomes problems of techniques that have previously been used, and provides a new, powerful scheme for understanding the behavior of complex interfacial systems.