(221c) Influences of Surfactant and Nanoparticle Assembly on Effective Interfacial Tensions

Assembly of surfactants or nanoparticles at air-liquid or liquid-liquid interfaces is important due to their wide applications. The application of surfactants is ubiquitous, ranging from natural and industrial processes to commercial and personal care products. However, many industrial processes are performed in the presence of both surfactants and nanoparticles. In spite of the importance, interfacial adsorption when a system contains both surfactants and nanoparticles has not been extensively studied. In this work, we have studied the assembly at air-water and liquid-liquid interfaces with an emphasis on the systems containing both surfactants and nanoparticles. Anionic surfactant, sodium dodecyl sulfate (SDS), and non-ionic surfactants, Triton X-100 and tetraethylene glycol monododecyl ether (C12E4), effectively decrease the surface tensions of air-water interfaces. The inclusion of negatively charged hydrophilic silica nanoparticles (diameters of approximately 13 nm) increases the efficiency of the SDS molecules but doesn't alter the performance of the non-ionic surfactants. The former is likely due to the repulsive Coulomb interactions between the SDS molecules and nanoparticles which promote the surfactant adsorption at air-water interfaces. For systems involving trichloroethylene (TCE)-water interfaces, the SDS and Triton X-100 surfactants effectively decrease the interfacial tensions and the nanoparticle effects are similar compared to those involving air-water interfaces. Interestingly, the C12E4 molecules, with or without the presence of nanoparticles, fail to decrease the TCE-water interfacial tensions. Our molecular dynamics simulations have suggested that the C12E4 molecules tend to disperse in the TCE phase rather than adsorb at the TCE-water interface.