Langmuir, Vol.16, No.2, 631-635, 2000
Long-range force of attraction between solvophobic surfaces in water and organic liquids containing dissolved air
An atomic force microscope has been employed to measure the force of interaction between a micron-sized colloidal sphere and a flat plate, both coated with a copolymer of perfluoro(2,2-dimethyl-1,3-dioxole) and tetrafluoroethylene (Teflon AF1600) in water, glycerol, formamide, ethylene glycol, ethylammonium nitrate, formic acid, ethanol, methanol, diiodomethane, 1-bromonaphthalene, hexadecane, and hexane. A long-range force of attraction was measured in water and, with the exception of the n-alkanols and n-alkanes, all the organic liquids. The results indicate that there is a macroscopic long-range attraction between solvophobic surfaces that has a different origin from that of the hydrophobic interaction observed at the molecular level, The results also indicate that there is a "solvophobic force" that is not due to either orientational ordering propagated by hydrogen bonds, electrostatic (or polarization) effects, or condensates of "loosely attached" surface material; all mechanisms that have been invoked previously to explain the macroscopic "hydrophobic force". The force curves measured in the organic liquids provide a new perspective which is consistent with the hypothesis that submicroscopic air bubbles adhering to the macroscopic surfaces are responsible for a long-range attraction.
Keywords:DER-WAALS-INTERACTION;HYDROPHOBIC SURFACES;AQUEOUS-ELECTROLYTE;FREE-ENERGIES;SURFACTANTS;MICROSCOPY;BUBBLE;SALT