Investigations of microemulsions by light scattering and neutron scattering

Abstract

Microemulsions formed from water, xylene, sodium dodecyl benzene sulphonate and hexanol have been investigated by three different scattering techniques, namely, time-average light scattering (l.s.), small-angle neutron scattering (SANS) and photon correlation spectroscopy (p.c.s.). The water volume fraction in this water-in-oil system, which was investigated at a constant molar ratio (hexanol: sodium dodecyl benzene sulphonate) of 3.28, was varied from zero to 0.533. Over most of the volume-fraction range the droplets were strongly interacting. The problem of obtaining information about the variation of particle size with volume fraction from scattering techniques in strongly interacting systems is discussed in some detail and a possible theoretical approach suggested based on the use of a hard-sphere interaction model. The combination of l.s., SANS and p.c.s. is shown to be an excellent one for problems of this type, in that l.s. and SANS can provide time-average structural information and p.c.s. dynamic information about the motion of the particles in strongly interacting systems. With the model proposed the information from the three experimental techniques was found to be self-consistent. For the system investigated the radius of the water core of the droplet was found to increase with increase in the water volume fraction whilst apparently maintaining a constant water–oil interfacial area.