CHAPTER 7: The Effect of Nanoparticles on the Oil–Water Interfacial Tension in the Presence of Nonionic Surfactants

Combining nanoparticles and surfactants has become increasingly important in recent approaches to bijel fabrication. This chapter illustrates the effect of silica nanoparticles (NPs) in combination with nonionic surfactants on the oil–water interfacial tension (IFT). Results from experiments and molecular dynamic simulations, mainly from our group, are summarized in this chapter. The interfacial tension of the oil−water system containing nonionic surfactants increases in the presence of silica NPs. The effect of silica nanoparticles on the diffusion and adsorption mechanism of the surfactant is analysed using different analytical models. Using coarse-grain molecular dynamics simulations it is observed that silica NPs in the absence of surfactant do not affect the oil–water IFT. However, depending on the amount of the surfactant adsorbed on the surface of the NPs, silica NPs may or may not affect the IFT values. The oil–water IFT increases with increasing amount of adsorption of the nonionic surfactant on the NPs. The cause of this adsorption is explained by atomistic molecular dynamics simulations.