(4dd) Micro-Scale Flow and Transport Phenomena in Chemical and Biological Systems

Rosenfeld, L., Stanford University

The effect of gravity and inertia dominate our experience of the physical world. However, as systems are reduced in size, phenomena such as diffusion, surface tension and viscosity become ever more important; at the micrometer scale they can dominate and result in a world that operates very differently from the macroscopic world we perceive and live in. There are numerous processes encountered in nature and industry where the microscale interaction of fluid-fluid interfaces is of central importance. These systems can involve fluid droplets and bubbles such as deformation of red blood cells in small capillaries, liquid membranes and phase separation processes.

My research interests are microscale transport phenomena, microstructure and physical properties of complex fluids and droplet-based microfluidics as a tool for chemical and biological systems.

I will describe here three different fundamental studies. In the first study I have addressed the interfacial flow and transport phenomena of droplets and bubbles in macro and micro gravity environments. The effort was directed to two avenues: spontaneous interaction due to interfacial transport and interaction induced by external gradients. In such drop-based systems, the presence of hybrid drops is usually of great interest. Their dynamics and deformation in viscous fluids is complex because of the existence of several interfaces. The study of these systems was done using conformal mapping techniques and numerical methods.

In the second study I have explored the transition from reversible to chaotic behavior in the oscillatory shear flow of water-in-oil emulsions. Emulsions are an important class of complex fluids with many applications in chemical, biological and industrial processes. The bulk rheological properties of these fluids are directly influenced by the dynamics at the microscopic level; hence a fundamental understanding of the microscopic dissipative rearrangements and specifically the transition from hydrodynamic reversible to irreversible behavior is of central importance. Here I have applied microfluidic techniques to study this fundamental behavior of the emulsion microstructure.

In the third study I have focused on the interfacial dynamics, rheology and stability of thin aqueous films covered with small molecule amphiphile monolayers. It was designed in order to study the stability of the tear film and dry eye disease treatment. A novel methodology to characterize dewetting of thin aqueous layers covered with insoluble surfactants was developed. Optical methods such as interferometry in order to detect the film thickness, scattering techniques in order to determine the monolayer’s molecular structure and interfacial and bulk rheology measurements to determine the macroscopic, mechanical properties of the films were employed.  

My goal is to establish a research program that will continue to pursue the dynamics of fluid-fluid interfaces. I am particularly interested in the effect of non-Newtonian rheology on interfacial flows as well as microhydrodynamic phenomena and its applications in microfluidic devices.