Bridging flocculation induced by competitive adsorption: implications for emulsion stability

Abstract

A new kind of bridging flocculation of colloidal particles arising from competitive adsorption between stabilizing components of different surface activity is explored using a simple statistical model. The simulated system consists of a circular cavity containing a single spherical particle and a large number of adsorbate molecules which interact with the particle surface and the cavity wall through a square-well potential. Bridging flocculation occurs when the particle and wall are separated by a monolayer of adsorbate molecules. Monte Carlo results show how, under certain conditions of adsorbate composition and adsorbate–adsorbent binding energies, bridging flocculation is present in the two-component system when it is absent in both the equivalent one-component systems at the same adsorbate density. The simulation gives a mechanistic explanation for the experimental observation of bridging flocculation in oil-in-water emulsions made with mixed biopolymer emulsifiers (protein + polysaccharide) at low emulsifier concentrations.