Optically-Driven Changes in Nanoparticle Solvation, Transport and Interaction

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Molecules within liquids organize themselves near solid surfaces in a range of different ways, a phenomenon called solvation. This organization plays a central role in important physical processes and technologies. For example, solvation underlies the use of liquids as lubricants to minimize friction between two surfaces or to control the assembly of nanoparticles of metals (for example, gold) into advanced materials for sensing. The central role of solvation in determining the properties of solid-liquid interfaces has motivated many past efforts aimed at changing solvation. Past efforts have included addition of salts to liquids or manipulation of temperature and pressure. This project moves beyond past studies by investigating the use of visible light to optically excite and change solvation of metal surfaces. The intensity and location at which light is delivered to a system can be readily manipulated, and thus the approach has the potential to make possible reversible and active control of solvation. The successful outcome of this research may provide the basis of new energy-efficient separations processes or new ways to create materials for low-cost sensor networks. This project will elucidate how optical excitation of nanoparticles can change their solvation, transport properties and phase behavior. The first thrust of research focuses on single nanoparticles, and elucidates how optical excitation of nanoparticles changes interfacial solvent structuring and thus nanoparticle hydrodynamic size. The second thrust of research examines how optically-induced changes in nanoparticle solvation alter pair-wise interactions, including electrical double layer and solvent-structural contributions. Measurements of probability distance distribution functions for pairs of nanoparticles will be inverted to obtain potentials of mean force. The third thrust of research investigates how optically-driven changes in nanoparticle solvation influence collective phenomena, such as the stability of dispersions of nanoparticles and their phase separation. The overall outcome of this program of research will be new knowledge of fundamental transport and phase separation processes arising from optically-driven changes in nanoparticle solvation.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.