A quasi-elastic neutron scattering study of water-in-oil microemulsions stabilised by aerosol-OT. Effect of additives including solubilised protein on molecular motions

Abstract

The quasi-elastic incoherent neutron scattering method has been used to investigate the mobility of surfactant and water molecules in single-phase oil-continuous microemulsions stabilised by sodium bis(2-ethylhexyl)sulphosuccinate (AOT). Addition of benzyl alcohol, which is adsorbed at the interface, or toluene effects little change in the lateral translational diffusion of AOT within the interface. Replacement of the dispersed water by glycerol results in a two-fold reduction in surfactant mobility. Solubilisation of α-chymotrypsin within the water droplet core of the microemulsion system causes no significant change in AOT mobility. However, spectra associated with water mobility in the enzyme-containing system clearly reveal the presence of 250–500 water molecules per protein molecule, which are ‘bound’ on the time scale of the experiment (6 × 10¹⁰ rad s^–1). The mobility of the remainder of the solubilised water in the system is unaffected by the presence of the enzyme.