(448h) Numerical Simulations of the Effect of Ionic Surfactant/Polymer on Oil-Water Interface Using Dissipative Particle Dynamics

The dissipative particle dynamics (DPD) is an ideal method to simulate such a coarse-grained system. DPD method can reproduce the forming process of the water-oil microstructure. In term of the effect of surfactants on emulsion structures, it is of fundamental importance to study the properties of emulsions. In this study, effects of the ionic surfactant (CTAB) and polymer (SMAc) on the oil/water interface are studied using dissipative particle dynamics (DPD) at the mesoscopic scale. Effects of the water content on equilibrated morphology of the oil/water emulsion are studied with the help of ionic surfactant. In addition, oil/water emulsion has the patterns of the compound emulsifier at the very low and very high water content. The interfacial tension increases, reaches maximum, and then decreases with an increase of water content. Both experiments and simulations show that the inorganic salts can improve the interfacial efficiency of the ionic surfactants, and lower the interfacial tension. The influence of polymer number is studied on their ability to reduce interfacial tension. The distributions of interfacial tension and mean interfacial density are predicted. The lower the interfacial tension and faster oil coalescence are, the more polymers is. In addition, the influence of the polymer on the surfactant aggregation behavior of the oil-water interface is discussed. The molecules of polymer (SMAc) are mainly gathering at the interface, where the surfactant molecules associate on the polymer chains in the composite oil/water/surfactant/polymer systems. The surfactant beads both located at the interface and associated on the polymer chains are in more upright and orderly arrangement at the interface with an increase of polymer number, as well as, the peak of polymer interfacial density become higher and broader. The interfacial tension impairment of the composite system is higher than that of the single system. The lower the interfacial tension and faster oil coalescence are, the more the polymer is. The model predictions reveal the basic mechanisms of ionic surfactant in the oil-water system and the coalescence process of oil and water droplets at the different ratio of water and oil. From these results, the conclusion can be made that the coarse grained model is a powerful and flexible tool to study emulsion processes in the oil-water systems, and further determines the properties surfactant and polymer in the emulsion processes.