Small angle neutron scattering of D2O–Brij 35 and D2O–alcohol–Brij 35 solutions and their modelling using the Percus–Yevick integral equation

Abstract

Small angle neutron scattering of direct micelles in binary surfactant–D₂O and ternary surfactant–alcohol– D₂O systems has been measured. The nonionic surfactant was poly(oxyethylene-23) lauryl ether (C₁₂E₂₃, commercial name: Brij 35) which was used at concentrations far beyond its critical micellar concentration: between 0.1 and 15 mass% (about 1.0×10^-3–1.5×10^-1 mol l^-1). The alcohols were butan-1-ol, pentan-1-ol, hexan-1-ol, and heptan-1-ol at concentrations of about 0.25 mol l^-1. The spectra could quantitatively be modelled by the Percus–Yevick integral equation method in combination with a core/shell model yielding detailed information about the size, the (ellipsoidal) shape, the aggregation number, the internal structure and the distribution of the micelles. The ternary systems were modelled with an additional parameter, the partition of the alcohol between the outer aqueous bulk and the inner micellar pseudo-phase. In the case of the pentanol system the partition coefficient inferred from NMR self-diffusion measurements was used to describe the scattering result.