(444g) Describing Emulsions in Terms of Pseudo-Potential Lattice Boltzmann Modeling

Liquid-liquid dispersions or emulsions are usually described in terms of densities and interfacial tension, while their mean droplet size and their droplet size distribution are assumed to depend on either shear rate (Capillary number) or (average) energy dissipation rate in the system. This phenomenological (or engineering) approach, however, does not explicitly and accurately represent the intermolecular interactions that lead to phase separation. On the contrary, the pseudopotential lattice Boltzmann model is excellently geared to describe such interactions between the constitutive components of a system, which lead to phase separation, and in this method the interfaces between phases are captured automatically. We use a pseudopotential lattice Boltzmann method for small density ratios  between the two liquid phases to study systems with three non-ideal components (described by the Carnahan-Starling EoS), one of which models a surfactant. We report a systematic study of the effects of the interaction strengths between the components and their reduced temperatures on the number and composition of the phases present at equilibrium. These results allow us to perform simulations of emulsions at prescribed density ratios between the two liquid phases. We also study how the surfactant component, which is present in small amounts relative to the other two components and repelled by both of them, is distributed between the interfacial region and the bulk phases. We determine how this third component alters the surface tension of the interfaces between the fluid phases.