IS THE LONG-RANGE HYDROPHOBIC ATTRACTION RELATED TO THE MOBILITY OF HYDROPHOBIC SURFACE GROUPS

Literature data show that there is a correlation between the lack of s tability, as indicated by contact angle hysteresis, of a hydrophobic s urface and the occurrence of a long-range (greater than or equal to 20 nm) attraction. In the case of hydrophobic monolayers adsorbed from s olution in situ, it has been shown that a shift of the adsorption/deso rption equilibrium on approach of the two surfaces can lead to a long- range attraction. For those surfaces where no adsorption/desorption eq uilibrium exists (Langmuir-Blodgett films, silylated surfaces, polymer surfaces), rearrangement or lateral diffusion of surface groups may b e possible. If the local density of hydrophobic groups is adjusted to give a decrease in free energy on approach of two surfaces, the result is an attractive interaction between the surfaces. Surfaces with no m obility of hydrophobic groups do not give rise to a long-range attract ion, as has been demonstrated experimentally for some polymer surfaces . These ideas explain the occurrence of a long-range attraction betwee n one hydrophobic surface and one hydrophilic surface, as well as in n onaqueous solvents. (C) 1997 Elsevier Science B.V.