Interaction between hydrophobic surfaces with metastable intervening liquid

Molecular simulation is used to elucidate hydrophobic interaction at atmosp heric pressure where liquid water between apolar walls is metastable with r espect to capillary evaporation. The steep increase of the estimated activa tion barrier of evaporation with surface-surface separation explains the ap parent stability of the liquid at distances more than an order of magnitude below the thermodynamic threshold of evaporation. Solvation by metastable liquid results in a short-ranged oscillatory repulsion which gives rise to an irreversible potential barrier between approaching walls. The barrier in creases with external pressure in accord with measured pressure-induced slo wing of conformational transitions of biopolymers with strong hydrophobic i nteractions. At a sufficiently small separation, the force abruptly turns a ttractive signaling nucleation of the vapor phase. This behavior is consist ent with the cavitation-induced hysteresis observed in a number of surface- force measurements for strongly hydrophobic surfaces at ambient conditions. (C) 2001 American Institute of Physics.