Y. Katsumoto et al., Evolutionary behaviour of miniemulsion phases: I. Hard sphere interaction and bound water on miniemulsion droplets, J PHYS-COND, 12(3), 2000, pp. 249-264
The interaction between nano sphere droplets in translucent oil in water (O
/W) emulsion phases, so-called miniemulsion phases, was investigated by usi
ng 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 changi
ng dispersed phase volume fraction phi', and it revealed the fact that the
osmotic compressibility is in good agreement with that of a hard sphere flu
id. The dependence of the collective diffusion coefficients, measured by dy
namic light scattering experiments, is similar to those observed in colloid
al 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 di
spersed droplets is given by phi = 1.35 phi'. Preparing miniemulsions with
various water to oil ratios, it was revealed that the ratio phi/phi' was va
ried from 1.01 to 1.33. This indicates that the underestimation of the tota
l volume of droplets calculated by the sum of surfactant and oil volume was
not negligible. It is therefore considered that the volume fraction of bou
nd water on miniemulsion droplets should be taken into account. We briefly
discuss the idea that bound water plays an important role in obtaining a ho
mogeneous miniemulsion phase.