Forces between Hydrophobic Solids in Concentrated Aqueous Salt Solution

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American Physical Society

Much research has focused on the discovery and description of long-ranged forces between hydrophobic solids immersed in water. Here we show that the force between high contact-angle solids in concentrated salt solution (1 M KCl) agrees very well with van der Waals forces calculated from Lifshitz theory for separations greater than 5 nm. The hydrophobic solids are octadecyltrichlorosilane-coated glass, with an advancing contact angle of 108 degrees. Thus, in 1 M salt solution, it is unnecessary to invoke the presence of a hydrophobic force at separations greater than 5 nm. Through measurement in salt solution, we avoid the necessity of accounting for large electrostatic forces that frequently occur in pure water and may obscure resolution of other forces.

Surfactant-coated surfaces, Monte carlo simulation, Long-range, Boundary-condition, Thin films, Attraction, Water, Microscopy, Particles, Interfaces, Physics
Mastropietro, Dean J. ; Ducker, William A., Mar 5, 2012. “Forces between Hydrophobic Solids in Concentrated Aqueous Salt Solution,” PHYSICAL REVIEW LETTERS 108(10): 106101. DOI: 10.1103/PhysRevLett.108.106101