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 stability, as indicated by contact angle hysteresis, of a hydrophobic surface and the occurrence of a long-range (greater than or equal to 20 nm) attraction. In the case of hydrophobic monolayers adsorbed from solution in situ, it has been shown that a shift of the adsorption/desorption equilibrium on approach of the two surfaces can lead to a long-range attraction. For those surfaces where no adsorption/desorption equilibrium exists (Langmuir-Blodgett films, silylated surfaces, polymer surfaces), rearrangement or lateral diffusion of surface groups may be 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 mobility of hydrophobic groups do not give rise to a long-range attraction, as has been demonstrated experimentally for some polymer surfaces. These ideas explain the occurrence of a long-range attraction between one hydrophobic surface and one hydrophilic surface, as well as in nonaqueous solvents. (C) 1997 Elsevier Science B.V.