From Spherical to Polymorphous Dispersed Phase Transition in Water/Oil Emulsions

Optical scanning tomography is used to characterize bulk properties of transparent water-in-paraffin oil emulsions stabilized with hexadecyl-trimethylammonium bromide (CTAB) and silica nanoparticles. A flow of 500 hundred images is used to analyze each scanning shot with a precision of about 1 ?m. The role of silica particles in the shape of the water droplets is investigated. Depending on the concentration of CTAB and silica nanoparticles, a transition occurs in their geometry that changes from spherical to polymorphous. This transition is controlled by the ratio R = [CTAB]/[SiO2] and is described using an identification procedure of the topology of the gray level contours of the tomographic images. The transition occurs for Rcrit ? 3 × 10-2 and is shown to correspond to a pH of the dispersed phase of 8.5.