Emulsion phase inversion of epoxies with non-ionic block emulsifiers: Effect of the emulsifier concentration on inversion phase and formation of spherical particles

Phase inversion emulsification technique, as a versatile method for emulsification of high-viscosity materials has received considerable attention in recent years due to its potential for producing particles of precise geometries, sizes, and size distributions. This report involves an investigation on the effect of emulsifier concentration on the inversion behaviour and the morphological aspects of the resulting solid epoxy particles. Emulsion inversion was induced by increasing the amount of initially dispersed deionized water in presence of a non-ionic block copolymer surfactant. The process of inversion was followed by monitoring the changes in the rotational speed of the stirrer. These changes are introduced in this study as a means to probe the viscosity variations of the emulsifying system during the process. It is shown that under a specific emulsifier concentration mainly the rod-shaped and ellipsoidal particles are formed. The fully spherical particles, however, were formed above this specific concentration. Further increase in the emulsifier concentration significantly reduced the size of spherical particles, controlled, and narrowed their random size and wide distributions. Dynamic light scattering analysis and scanning electron microscopy were used to study the particles size and distribution. In addition, the study of rotational speed variations of the stirrer which is directly related to the viscosity changes of the emulsifying system revealed that during the inversion process a correlation could be established between the physical aspects of the inversion behaviour and the viscosity changes.