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Show posters on the hill Molecular Diffusion in an Opal Modified Electrode Michael Newton, Henry S. White, Department of Chemistry o, 'pals are of interest because of their applications in photonic crystals, energy storage media, novel magnetic materials, sensors, and nano-particle detection. An opal is an ordered lattice of nanometerscale spheres. In these experiments, molecular diffusion through a thin layer of an opal was investigated by electrochemical methods. Diffusion is defined as the random motion of molecules across a chemical or energy gradient. Diffusion coefficients for several molecules in the opal, were determined by measuring the flux of the molecule across the thin layer opal. From the diffusion coefficients, the opal tortuosity was then determined (t), which accounts for the added distance the molecule must traverse to pass through the opal. Values obtained for t from the tests were then compared to values of t obtained from computer simulations of an infinitely thick opal film. A value of t=3.0 was obtained from the simulations. The experiments yield t=1.9 and t=3.1 for two different molecules. Differences in the values of t may be due to defects in the opal, which allow molecules to diffuse more freely through the film. Maxwell first considered diffusion through a lattice of spherical particles over one hundred years ago. Through these ex- Molecular Diffusion in an Opal Modified Electrode Michael Newton, Henry S. White, Department of Chemistry Dependence of rv /D^ , wild fraction. and UirtuuMI> on the number of la of spherical particle* and direction of the transport normal to the planes. periments, we have determined the diffusion rates in opals as a function of the crystal orientation. We are currently modifying the surface of the spheres to selectively control transport based on electrostatic interactions, with the goal of developing chemical sensors. |