Interfacial water from molecular to mesoscopic scale and its relation to tunable hydrophobicity

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Alenka Luzar of Virginia Commonwealth University is supported by an award from the Chemical Theory, Models and Computational Methods program in the Chemistry Division to carry out research on reversible wetting transitions and nanowetting of surfaces with topological and chemical heterogeneities. The methodologies include a combination of theory and simulation techniques in statistical mechanics and development of computational algorithms to deal with interfacial properties of water in nanoconfined spaces. Three specific problems are being investigated: (1) electric field or pressure-induced transitions on superyhdrophobic surfaces to achieve reversible switching between contrasting Cassie and Wenzel states; (2) nanodroplet actuation on an electrode to provide a detailed and self-consistent microscopic picture of drop and electrode dynamic responses under applied voltage, at conditions where continuum physics offers at best very crude predictions; and (3) probing the extent of surface force additivity on chemically heterogeneous substrates to address how well they can predict forces between mixed surfaces from those between pure ones.The research has broad impact on many disciplines including materials science, engineering, and biology. Molecular level understanding of intelligent control of surface hydrophobicity by external stimuli can find real-world applications in nano-fluidics and electro-optics. The first topic elucidates if reversible switching between wetting-resistant and hydrophilic behavior of a material is achievable at the nanoscale under electric and/or pressure control, and what are the time scales involved. The second topic concerns the design of nano-sized optical elements under electric control. They want to learn if tunable optical devices can be miniaturized to the nanoscale level, and what could be the essential advantages or challenges in comparison to macroscopic ones. The third topic impacts research into self-assembling materials studied in nanotechnology, as well as biophysics.