Measurement of the Long- and Short-Range Hydrophobic Attraction between Surfactant-Coated Surfaces

We have measured the attractive long-range ‘hydrophobic' forces in water between double-chained surfactant monolayers physisorbed on mica. We used both normal and high-speed video cameras to follow the dynamics and possible rate-dependence of force−distance profiles in the distance regime from 1000 Å to adhesive contact, including the short-distance regime below 100 Åthe regime of greatest biological interest. We find that the hydrophobic interaction follows a double-exponential function down to separations of ∼50 Å, after which point the attractive force appears to become considerably stronger.