A Mesoscale Dynamics study of the phases in surfactant-water ternary systems

Abstract

A mesoscale dynamics simulation using a Dissipative Particle Dynamics regime was developed to investigate the ability of small molecules to control phase structures in non-ionic surfactant-water systems. The ability to control phase structure has positive implications for potential templating applications which require ordered and stable phases with high surface curvature. The phases present in such systems were successfully modelled, the results of which compare well with experiment. Additives which decreased the surface curvature of the interfacial region included oils and long-chained alcohols. These molecules destabilised high-surface curvature phases, such as the bicontinuous cubic and mesh phases, in favour of the lamellar phase.

However, the addition of anaesthetics and short-chained alcohols, which are small amphiphilic molecules, promote surface curvature, and there is an optimum chain length for maximum stability of the mesh phase. Coulombic interactions, although unsuccessfully modelled with the simulations, were found to be important through Langmuir trough investigations adding ionic and nonionic anaesthetics to non-ionic surfactant and ionic lipid monolayers, as ionic monolayer-anaesthetic combinations showed a larger increase in surface pressure compared to the non-ionic monolayer-anaesthetic combination. It is therefore very difficult to engineer phase structures for templating applications because the extreme chemical environment in the templating solution would serve to destabilise any high surface curvature these additives would stabilise.