Formation and properties of paraffin wax submicron emulsions prepared by the emulsion inversion point method

Paraffin wax-in-water submicron emulsions stabilized by Span 80/Tween 80 were prepared by the emulsion inversion point (EIP) method. Stable emulsions with droplet diameters about 700 nm could be formed when the hydrophilic–lipophilic balance (HLB) values are between 9.5 and 10.3 and the surfactant-to-oil ratio is above 0.2. Increased emulsification temperature and cooling rate were found to improve the emulsion properties. Either mixing all components together or addition of oil to the aqueous surfactant dispersion could not produce stable emulsions. Optical microscopy and scanning electron microscopy (SEM) were used to study the morphology of the emulsion droplets. The droplets were solid at room temperature, showing bright spots under polarized light and an irregular spheres shape under SEM. Due to homogeneous nucleation in the finely dispersed emulsion droplets, the emulsion shows a large degree of undercooling (15 °C) in the differential scanning calorimetry (DSC) thermogram. The emulsions became unstable with heating, but remained stable under cooling. The electrophoretic properties of emulsion droplets showed a negative zeta potential, which was increased with the pH of the system due to the adsorption of hydroxyl groups.