|M.Sc Student||Bittoun Eyal|
|Subject||Emulsions Stabilized by Colloidal Particles|
|Department||Department of Chemical Engineering||Supervisor||Professor Emeritus Abraham Marmur|
Solid-Stabilized emulsions (Pickering emulsions) consist of drops of one immiscible liquid in another, stabilized solely by solid particles. These emulsions are prepared in the absence of any surface active species like surfactant molecules, amphiphilic polymers or proteins as in conventional emulsions.
Recently, there has been resurgence of interest in this field as a result of current activity in nanoparticle technology for producing new materials. Research and development activity in this field can be found in paint coatings, preparation of core-shell colloid particles of various structures and compositions, micro-capsules for encapsulation of drugs, enzymes and nanostructured surfaces for photoelectrochemical and photocathalytic processes.
The stability of Pickering emulsions is explained in the literature by high energy of "attachment" of the particles to the water-oil interface. This energy depends on the wettability of the particles at the water-oil interface, quantified by the contact angle qY that water makes with the particles.
This thesis dealt with thermodynamic aspects of emulsions stabilized by solid particles. The investigation of such emulsions was made by theoretical modeling considering the surface energies of the tri-phase system. The effect of various parameters on the stability of the emulsion was studied.
The results showed that Pickering emulsions, of both type (o/w and w/o), stabilized with spherical particles of equal size cannot be thermodynamically stable. There is a phase separated state which has always a lower Gibbs energy of the emulsion state.
It was also shown that high energy barriers for removal of the particles from drop surfaces to one of the liquid phases is the source of the high kinetic stability of Pickering emulsions. Most stable o/w and w/o emulsions are obtained around qY=700 and qY=1100 respectively. This novel approach of energy barriers calculation gives a very good explanation to many experimental results governing the emulsion stability.