Alkane-tolerant worm-like micelles based on assembled surfactants

Abstract

Self-assembly of surfactants in aqueous solution can form a variety of aggregate structures, among which worm-like micelles (WLMs) have attracted much attention due to their excellent viscoelasticity. The addition of oil often leads to a decrease in the viscosity of WLMs, which is closely related to the location of oil dissolution within the WLMs. Whether oil could induce a viscosity increase in WLMs caught our attention. In order to explore the effect of alkanes on the microstructure of different WLMs systems, three WLMs systems were prepared using three surfactants: oleic acid-N,N-dimethylcyclohexylamine (OA-DMCHA), sodium oleate-chlorinated sodium (NaOA-NaCl) and cetyltrimethylammonium bromide-sodium salicylate (CTAB-NaSA). The changes of parameters such as viscosity, microstructure of these systems before and after the introduction of alkanes were analyzed. The relationship between the alkane concentration and the interlayer spacing of the lamellar phase was investigated by small angle X scattering (SAXS). Except for OA-DMCHA, the structures of the other two systems were destroyed after the addition of alkanes. Considering the solubility of surfactants in organic alkanes, it was found that alkanes can enter the hydrophobic barrier layer of OA-DMCHA. The initial WLMs transformed into a lamellar phase, and the interlayer spacing of the lamellar phase increased with increasing alkane concentration.