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 microm. 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 approximately 3x10(-2) and is shown to correspond to a pH of the dispersed phase of 8.5.