(33a) Recent Progress In Understanding the Hydrophobic Interaction: Is There a Generic Hydrophobic Interaction Potential?

The current situation is concerning the existence or otherwise of a hydrophobic interaction potential between surfaces (rather than molecules) will be reviewed. The review will cover both old and new SFA and AFM experiments in the all-important short-range regime at surface separations below 2 nm down to hemi-fusion contact. I will also present recent SFA results (by co-workers Steve Donaldson, Ted Lee and Brad Chmelka) on the approach, jumps into contact, adhesion and hemi-fusion of surfactant bilayers that have allowed us to quantitatively assess the separate contributions of van der Waals, double-layer, steric-hydration, bilayer elasticity, and hydrophobic forces at small (~nm) separations. We propose a model that includes an exponentially attractive hydrophobic term (which acts only when the headgroups expose an area above their equilibrium or ‘optimum’ head group area) that adequately models the fusion/hemi-fusion instability and the magnitudes and separations of the energy maximum (just before fusion) and adhesive minimum (at hemi-fusion contact of the surfactant chains).