Effects of chain length of surfactants and their adsorption on nanoparticles on stability of CO2-in-water emulsions

Abstract

Hydrophilic silica nanoparticles (NPs) were employed to stabilize CO2-in-water (C/W) emulsions with three cationic homolog surfactants. In order to explore the effect of surfactant adsorption different alkyl chain lengths and concentrations on the NP surface on NPs’ potential and agglomeration size, zeta potential, particle size analysis and adsorption isotherms were quantitatively characterized by experiments. The distribution of interfacial active substances at the interface affected the emulsion stability. Therefore, the influence of surfactant adsorption on the interfacial properties of NPs was determined by surface tension and contact angle characterization. The results demonstrated that surfactant adsorption on NPs would form vertically oriented bilayer adsorption owing to an increase in surfactant concentration. Surfactants adsorbed onto negatively charged NPs as a monolayer due to electrostatic attraction of hydrophilic head groups, leading to the increase of NPs’ hydrophobicity. Sufficient surfactant bilayer adsorption on the NP surface by virtue of tail chain interactions also altered particles’ wettability. The equilibrium adsorption values of the homologous surfactants on the NP surface were almost identical. However, for the synergistic emulsification of single surfactant and NPs, the surfactant with the longer alkyl chain would achieve its optimum performance with NPs at the lower concentration.