Vsj. Craig et al., Direct measurement of hydrophobic forces: A study of dissolved gas, approach rate, and neutron irradiation, LANGMUIR, 15(4), 1999, pp. 1562-1569
Theoretical interpretations of the, as yet, poorly understood long-range hy
drophobic attraction are briefly reviewed. We report long-range hydrophobic
attractive forces between silica surfaces made hydrophobic by adsorption o
f the cationic surfactants cetyltrimethylammonium bromide and cetylpyridini
um chloride onto silica surfaces. The effects of dissolved gas, surface app
roach velocity, and neutron irradiation on the measured interaction Have be
en studied in order to investigate possible non-electrostatic mechanisms fo
r the long-range hydrophobic attraction. At large separations the presence
of dissolved gas, neutron irradiation, and reduced approach velocities are,
in each case, found to result in a stronger attraction between the hydroph
obic surfaces. These results are consistent with mechanisms related to the
metastability of the thin aqueous film separating the approaching hydrophob
ic surfaces.