STUDY OF THE LONG-RANGE HYDROPHOBIC ATTRACTION IN CONCENTRATED SALT-SOLUTIONS AND ITS IMPLICATIONS FOR ELECTROSTATIC MODELS

Direct force measurements of the interaction between silica surfaces i n low concentrations of the soluble cationic surfactant cetyltrimethyl ammonium bromide reveal a long-range strongly attractive hydrophobic f orce extending out to 100 nm. Similar forces observed for cetylpyridin ium chloride in 0.1 M electrolyte demonstrate that the hydrophobic att raction is undiminished in the presence of concentrated electrolyte. T hese results are discussed in relation to other investigations of the long-range hydrophobic attraction and lead to the conclusion that elec trostatic double layer forces are unable to account for these attracti ve forces.