Evolutionary behaviour of miniemulsion phases: I. Hard sphere interaction and bound water on miniemulsion droplets

Abstract

The interaction between nano sphere droplets in translucent oil in water (O/W) emulsion phases, so-called miniemulsion phases, was investigated by using light scattering measurement techniques. We choose the ternary system of water/hexadecane/Mergital LT7 (the main component is heptaethylene glycol mono-n-dodecyl ether). Rayleigh ratio measurement was performed with changing dispersed phase volume fraction ´, and it revealed the fact that the osmotic compressibility is in good agreement with that of a hard sphere fluid. The dependence of the collective diffusion coefficients, measured by dynamic light scattering experiments, is similar to those observed in colloidal hard sphere suspensions. We found out that the ratio of the hydrodynamic diameter to the hard sphere diameter is 1.19 and the volume fraction of dispersed droplets is given by = 1.35´. Preparing miniemulsions with various water to oil ratios, it was revealed that the ratio /´ was varied from 1.01 to 1.33. This indicates that the underestimation of the total volume of droplets calculated by the sum of surfactant and oil volume was not negligible. It is therefore considered that the volume fraction of bound water on miniemulsion droplets should be taken into account. We briefly discuss the idea that bound water plays an important role in obtaining a homogeneous miniemulsion phase.