Extended Q-range small angle neutron scattering from inverse micellar solutions of PIBSA—Micelle and molecular scattering

Inverse micelles play an important role in the stability of high internal phase water in oil (W/O) emulsions. The influence of both solvent and temperature has been investigated on the structure of inverse micelles prepared from the polyisobutylene-based surfactant, PIBSA, using small-angle neutron scattering (SANS). By collecting data over an extended range of scattering vector (Q), combined with the use of solvent deuteration, SANS has highlighted an additional contribution to the anticipated micellar scattering, namely a signal characteristic of rod-like scattering that is consistent with single dissolved molecules of the PIBSA surfactant and its primarily hydrogenated (mainly alkane oil) solvent (both MW ca. 1000 Da). The solvency effect of three different solvents (hexadecane, cyclohexane and toluene) on micellar–monomer (rod) equilibrium has also been evaluated. The volume fractions of rods and micelles in solution are found to agree with the sample compositions, as does the intensity of the observed incoherent background. This consistency across fit parameters not only highlights the sensitivity of the model but also the value of extended Q range, enhanced signal-to-noise studies in such soft matter systems. The data show the extent to which quantitative measurements can be carried at the molecular level using small angle scattering.