Development of a General Interaction Potential for Hydrophobic and Hydrophilic Interactions with Applications to Wetting and Contact Angles

Seminar series
Physical Chemistry Seminar
Mon, Mar 11 4:00pm to 5:00pm
2033 Young Hall
Speaker Professor Jacob N. Israelachvili
University of California, Santa Barbara
Dept. of Chemical Engineering

We have carried out surface force measurements between surfactant-bilayer coated surfaces whose hydrophobicity could be reversibly modulated by light activation, and have obtained a possibly universal interaction potential for the attractive interaction between surfaces whose hydrophobicity varies from f=0 (fully hydrophobic surfaces, interfacial energy ~50 mJ/m2) to f=1 (no hydrophobic interaction). A picture is emerging that suggests that both hydrophobic and hydrophilic interactions can be described by the same equation, that is, for f>1 the equation also appears to quantitatively describe the additional repulsive ‘hydration’ force between naturally hydrophilic surfaces or surfaces rendered hydrophilic by the adsorption of hydrated ions. A universal exponential decay length of ~1.0 nm is proposed for both interactions. The equation also relates the orientations of surfactant molecules in adsorbed monolayers to their interfacial energy and, in turn, to water contact angles, and especially the molecular (reorientation) processes and dynamics associated with contact angle hysteresis effects.