Oil-induced formation of branched wormlike micelles in an alcohol propoxysulfate extended surfactant system

Abstract

The addition of oil to an extended surfactant–water system (sodium tetrapropylene glycol (2-ethyl)octyl ether sulfate, C₁₀PO₄SO₄Na) induces the elongation of spherical micelles into oil-swollen branched wormlike micelles (WLMs) near the phase inversion point of the surfactant–oil–water (SOW) system. The hydrophilic–lipophilic-difference (HLD) framework, which has been associated with surfactant curvature, was successfully used to predict the conditions under which WLMs are produced for both polar and non-polar oils. At HLD = 0, the formation of low-curvature surfactant structures including WLMs and liquid crystals are favored in water-rich systems. Micellar growth begins around HLD = −0.5, and reaches a plateau upon the formation of a branched WLM network at HLD = 0. Above the entanglement concentration, the branched WLMs exhibit Maxwell and shear thinning behavior which is suitable for the suspension of nanoparticles, among others.