Structure and Dynamics of Composite, Fluid Interfaces

Stanford University, Stanford CA

Investigators

Abstract

The proposed research will investigate the dynamics and structure of composite, fluid interfaces comprised of combinations of colloidal particles and molecular amphiphiles. Two-dimensional suspensions of asymmetric particles will also be studied. Since many commercial and naturally occurring systems (emulsions, foams, and the alveoli in our lungs) are complex mixtures of amphiphilic materials, fundamental understanding of their interfacial rheology is central to advancing the performance of products and treatment procedures. This work, which is primarily experimental, will take advantage of new measurement methods developed in our laboratory (interfacial rheometry, interfacial flow-microscopy) to reveal the relationship between interfacial microstructure and interfacial rheology. This work will focus on mobile interfaces comprised of colloidal particles that coexist with molecular amphiphiles. This results in two-dimensional suspensions that are expected to have a unique rheological character. In addition to spherical, colloidal particles, prolate and oblate particles will be studied since these systems offer the possibility of mimicking fatty acids and alcohols where positional and orientational order come together to create complex 2D phase diagrams. Intellectual merit. Complex fluid interfaces can be classified in ways that are similar to their complex fluid counterparts (2D melts, solutions, suspensions, etc.). Indeed, restricting molecules and particles to two dimensions often increases rheological nonlinearities. Most physical systems, however, are mixtures of amphiphilic constituents, but little attention has been offered in this direction. The experiments planned here will provide the first systematic data on two-dimensional suspensions where particles are collected within monolayers on nonNewtonian, molecular amphiphiles. Broader impacts. The interfacial rheology of complex, composite monolayers is important to many commercial activities, such as the processing of food products and personal products. These systems are often in the form of emulsions and foams that require stabilization. Furthermore, colloidal systems are useful model systems for the study of basic physical phenomena and in this case two-dimensional monolayers comprised of asymmetric particles will be used to mimic the rich phase behavior of fatty acids and phospholipids.