Particles as stabilizers and wetting modifiers in colloidal multiphase systems

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Zhang, Yi
Behrens, Sven H.
Meredith, J. Carson
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Common colloidal systems such as particle suspensions, foams, and emulsions are simply fine dispersions of one phase in another. More complex systems containing multiple dispersed fluids (gas bubbles and liquid droplets or droplets of different immiscible liquids) also occur naturally and even play increasingly important roles in industrial applications such as cosmetics, pharmaceutical formulations, water purification, or food processing. Their various applications depend both on their stability and on their intrinsic wetting morphology. Surfactants traditionally serve as stabilizers and wetting modifiers, but solid particles can sometimes achieve the same goal; moreover, they can have the advantage of providing better resistance to harsh application conditions, posing fewer environmental concerns, and allowing for easier recovery. As part of my doctoral research on particles as stabilizers in a colloidal multiphase system, I discovered a new class of foam material, capillary foam, which is obtained by frothing a particle suspension in the presence of a small amount of oil. I studied the stabilization mechanism, formation stages, effects of process parameters, and various applications of capillary foams. In addition to serving as co-stabilizers, it has been discovered that colloidal particles can be used as efficient wetting modifiers. In the final part of my thesis, the interfacial activity of isotropic silica nanoparticles is analyzed. It is demonstrated that isotropic particles can change interfacial tensions as long as they are delivered to and have strong affinity for the interface. A thermodynamic model is developed to estimate the effective interfacial tensions and packing density of particles in fluid-fluid interfaces, which matches the experimentally measured results.
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