Catastrophic phase inversion of ellipsoids stabilized emulsion - Role of surface modification

Abstract: In this work, a systematic investigation of catastrophic phase inversion of emulsions stabilized by ellipsoidal particles is carried out. In particular, we consider the role of surface modification of particles and their dispersibility in different phases in the context of catastrophic phase inversion. In our experiments, we model monodisperse hematite ellipsoids and modify their surface to a different degree by oleic acid treatment. The effect of the oil-water ratio on the formation and stability of solid stabilized emulsions is studied by considering (i) particle-laden aqueous phase and oil, (ii) water and particle-laden oil phase, and (iii) particle-laden aqueous phase and particle-laden oil phase. Interestingly, when homogenized with oil, aqueous dispersions that contain either unmodified or partially modified hematite ellipsoids did not show any phase inversion when the oil-water ratio was varied. On the other hand, the oil phase dispersed with hematite ellipsoids whose surface is partially or fully modified with oleic acid, when homogenized with water, is found to exhibit catastrophic phase inversion. Moreover, when aqueous dispersions with pristine hematite ellipsoids and oil phases containing fully modified hematite ellipsoids are emulsified, catastrophic phase inversion is observed as the oil-water ratio is varied. The main findings of our work are that the oil-to-water ratio at which catastrophic phase inversion occurs can be tuned by particle surface modification and by dispersing particles in different phases used for emulsification.