DIRECT MEASUREMENT OF STRUCTURAL FORCES IN A SUPERMOLECULAR FLUID

The force as a function of separation between two mica surfaces immersed in a reversed micellar system sodium bis(2-ethyl hexyl) sulfosuccinate (AOT)/water/heptane was measured for a range of concentrations with size and polydispersity of the micelles constant. A piezoelectric bimorph force sensor was used which produces a charge proportional to the load. At low micellar volume fractions the force is a purely attractive van der Waals interaction, while at higher concentrations, the force-distance profile oscillates with a period equal to the size expected for the micelles. The measured interaction is lower in magnitude than theoretical values for a monodisperse hard-sphere fluid between hard walls.