From Oil-Swollen Wormlike Micelles to Microemulsion Droplets: A Static Light Scattering Study of the L1 Phase of the System Water + C12E5 + Decane

Abstract

The microstructure of the ternary system pentaethyleneglycol monododecyl ether (C12E5), decane and water was investigated by static light scattering in the water-rich region of the phase diagram at constant temperature (22 °C). Micellar size and shape were determined along several pseudobinary sections of constant oil-to-surfactant ratio. The main focus was on dilute solutions (cm ranging from 0.0004 g cm-3 up to 0.3 g cm-3, where cm denotes the mass concentration of oil plus surfactant in the aqueous phase) and small oil content (α up to 0.35, where α denotes the mass fraction of oil in the oil + surfactant mixture). Our data analysis supports the presumed existence of wormlike micelles at low α. The concentration dependence of the apparent molar mass Mapp of the micelles can be represented over a wide concentration range (up to the semidilute regime) by a model that combines a power law Mw ∝ cma with the structure factor S(q = 0) for flexible polymer chains in good solvents. For α ≤ 0.10 the fitted valu...