SUBMICROCAVITY STRUCTURE OF WATER BETWEEN HYDROPHOBIC AND HYDROPHILIC WALLS AS REVEALED BY OPTICAL CAVITATION

Laser-induced cavitation in a thin water layer bounded by hydrophobic and hydrophilic surfaces has been explored. For hydrophobic surfaces, the cavitation probability is enhanced and its threshold lowered, For hydrophilic walls, the formation of a macroscopic gas bubble during the laser pulse is consistent with earlier work on the existence of submicrobubble (bubston) clusters in bulk water (Bunkin et al., submitted for publication; Bunkin and Lobeyev, JETP Lett. Engl. Transl. 58, 91 (1993)). The increased cavitation probability observed with hydrophobic surfaces can be linked to an enhanced concentration of gas-filled submicrocavities close to the surface as compared to those in bulk water. The phenomenon appears to be closely related to the long-range hydrophobic interactions between surfaces and to the slippage of water over hydrophobic surfaces. (C) 1995 Academic Press, Inc.