Foams and Emulsions: the Importance of Structural Forces

Abstract

We present a brief summary of the salient findings of our recent research delivered as a keynote lecture at the Australian Conference on Colloid and Interface Science held in Sydney in February 2007. We have developed a hybrid surface force apparatus (thin film capillary force balance) in conjunction with differential interference microscopy to show the phenomenon of microstructuring or stratification in thin films containing surfactant micelles, proteins, and nanoparticles separating two bubbles or droplets, as in foam and emulsion systems. The structural disjoining pressure, i.e. the structural force, arising because of the ordered microstructure formation inside thin liquid films between bubbles or drops, offers a new stabilization mechanism for foams, emulsions, and fluid-particle suspensions. In addition to the thin film approach, we also used both the Kossel diffraction and direct digitized optical imaging methods to directly observe the structure and stability of foam and emulsion systems. Our experiments were complemented by computations involving Monte Carlo simulations and the integral equation of statistical mechanics.