Article

Effect of Salts and Dissolved Gas on Optical Cavitation near Hydrophobic and Hydrophilic Surfaces

Langmuir (Impact Factor: 4.38). 05/1997; 13(11). DOI: 10.1021/la960265k

ABSTRACT The effect of four 1:1 electrolytes (KCl, KBr, NH4Cl, and CH3COONa) on optical (stimulated by laser pulse) cavitation in thin layers bounded by hydrophobic and hydrophilic surfaces has been explored. For water and all salts (up to 1 M) in the case of hydrophobic surfaces, the cavitation probability is enhanced as compared with the case of hydrophilic walls. The increased cavitation probability observed with hydrophobic surfaces can be linked to an enhanced concentration of gas-filled submicrocavities close to them. The phenomenon seems to depend strongly on dissolved gas. Variations in the probability of cavitation that occur with electrolyte are significant and depend on its concentration and type. The specific effect of electrolytes on optical cavitation in a thin layer likely makes sense only in terms of the previously neglected ionic dispersion interactions. The results obtained may have implications for the mechanisms of the long-range hydrophobic interactions between surfaces and hydrophobic slippage.

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    [Show abstract] [Hide abstract]
    ABSTRACT: Interaction of bubbles with solid surfaces is considered with respect to approach/contact, film rupture, and bubble attachment, with particle separation by flotation the classic example. During approach/contact bubble deformation may occur and the interaction involves momentum transfer as described by hydrodynamic forces. Subsequent interaction involving film rupture is governed by interfacial forces including van der Waals forces, electrostatic forces, hydration forces, and hydrophobic forces. The structure and stability of the film is considered with respect to interfacial water structure and the presence of surface stabilized, nanosized gas bubbles. Featured properties of the solid surface (roughness, heterogeneity) have a significant influence on water film stability and rupture. Finally the bubble attachment is examined in terms of the three- phase line of contact, its formation and relaxation.

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