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Structure, Dynamics and Thermodynamics of Water Confined by Surfaces with Patterned Hydrophobicity

Pablo G. Debenedetti1, Nicolas Giovambattista1, and Peter J. Rossky2. (1) Chemical Engineering, Princeton University, A-419 Engineering Quadrangle, Princeton, NJ 08544, (2) Department of Chemistry and Biochemistry, University of Texas, Austin, Austin, TX 78712

We present results from molecular dynamics simulations of SPC/E water confined by surfaces with adjustable hydrophobicity. For purely hydrophobic walls we compute a phase diagram at 300K in the (pressure, separation) plane over the range -500 bar < P < 2kbar, 0.4 < d < 1.6 nm, showing the regions where the vapor, liquid, and bilayer ice phases are stable. The liquid phase is always stable for hydrophilic confinement over the range of conditions explored. Water structure is found to be sensitive to pressure for hydrophobic confinement, but not in the hydrophilic case. For chemically heterogeneous surfaces with hydrphobic and hydrophilic "patches" we find complex behavior including geometry- and length-scale-dependent hydrophobicity, as well as pattern-dependent drying kinetics. The results suggest that the relationship between drying, hydrophobic collapse and protein folding is more complex than hitherto assumed. We also investigate the gradual disappearance of differences between hydrophobic and hydrophilic confinement upon pressurization.