POWRE: Constrained Diffusion of an Isolated Colloidal Sphere in Confined Geometry

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9870437 Lin This project probes the effects of confined geometry on the diffusion of an isolated colloidal sphere using optical tweezers combined with digital video microscopy. The program is divided into two distinct groups of experiments based on the nature of the confined geometry. In the first group of experiments, the diffusion of an isolated sphere near one planar wall or confined between two parallel planar walls will be studied. Optical tweezers will be used to manipulate the position and the diffusion range of the sphere with respect to the walls. The main issue in these experiments involves the effective wall drag force on a neutral or charged sphere from a neutral or charged smooth glass wall or from a "structured wall" such as a 2D colloidal crystalline surface. In a second group of experiments, the diffusion of a sphere trapped in a one-dimensional tunnel or two-dimensional network of tunnels will be studied. The tunnels or tunnel-network with a well-defined spatial structure will be fabricated by microcontact printing. These experiments probe the correlation of the diffusion of a sphere to the spatial structure of the ambient patterned confined geometry. The issues being addressed are of fundamental interest for understanding colloidal hydrodynamics. The model systems noted above are limiting cases representing problems associated with diffusion of macromolecules either at interfaces or in random porous structures. Examples include transport processes such as "single file diffusion" in physical mixing processing, electrodiffusion of polyelectrolytes in confined environments (electrophoresis in sequencing large DNA molecues), microbubble diffusion at liquid/crystal interfaces of a growing crystal front, fine particle migration and flow of stable emulsion drops in porous media (relevant to oil recovery processes). %%% This is a research enhancement grant made under the Professional Opportunities for Women in Research and Education (POWRE) program. T he research will contribute new materials science knowledge at a fundamental level.