Fundamental New Experiments on Molecular Diffusion in Complex Solutions: Amplitude-Calibrated Forced Rayleigh Scattering

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In this RUI project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Spiegel will utilize amplitude-calibrated forced Rayleigh scattering (AC-FRS) to investigate small-molecule diffusion in polymer solutions. This method will be used to measure photoproduct and ground-state probe diffusion in order to develop in-situ optical control of molecular diffusion through polymer solutions and solids, including nonlinear-optical polymer waveguides. Initial experiments will examine photoinduced changes in the diffusion coefficients of azobenzenes and spiropyrans within polar-pendant group polymers. The diffusion of uncharged molecules across microscopic lengths through complex solutions such as polymers is a commonly occurring process in chemistry, chemical engineering, and biology. Nonetheless, there are many fundamental physical issues which have not been addressed. This project will look at some of the interactions which are important in understanding how to use light to control the rates of diffusion of neutral particles in polymer solids and solutions. This type of phenomenon has implications for high-speed nonlinear fiber optics technology.