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Title: Stabilisation and destabilisation of Pickering emulsions
Author: Zheng, Raojun
ISNI:       0000 0005 0287 7444
Awarding Body: University of Hull
Current Institution: University of Hull
Date of Award: 2020
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In this thesis, the stabilisation and destabilisation of Pickering emulsions have been investigated. Organic electrolytes are added to hydrophilic silica and partially hydrophobic polystyrene latex particle dispersions to enable them to stabilise emulsions. A series of tetraalkylammonium salts (R4NX, X is an anion) is added to aqueous dispersions of hydrophilic silica particles, with the alkyl chain (R) systematically increasing from 1 (methyl) to 4 (butyl). The adsorption of R4N+ ions onto particle surface reduces the surface charge which increases the particle hydrophobicity. Consequently, the stability of oil-in-water (o/w) emulsions increases with salt concentration and the R chain length. In addition, we compare the arrangement of micron-sized silica particles at both curved droplet interfaces and at a planar oil-water interface in the presence of the butyl analogue. Tetrapentylammonium bromide (TPeAB) and sodium thiocyanate (NaSCN) induce charge reversal of negatively charged sulfate (SO4-) and positively charged amidine (C(NH)NH3+) latex particles, respectively. However, charge reversal of particles hardly influences the type or stability of emulsions. Water-in-oil (w/o) emulsions are preferentially stabilised by both types of particles with dodecane. In systems with carboxyl latex particles, no charge reversal is induced by TPeAB at studied concentrations. However, emulsions invert from w/o to o/w upon increasing TPeAB concentration when PDMS (silicone oil) of viscosity 1 cS and 50 cS is used as the oil phase. It is intriguing that the surface charge of particles plays a minor role in the stabilization of emulsions whereas the hydrophobic polystyrene part dominates the emulsion type. In addition, the destabilisation of both w/o and o/w Pickering emulsions using solid particles is explored. Destabilizers adsorb onto oil-water interfaces with the help of gentle stirring. If the particles are more wetted by the inner phase of droplets, the adsorbed particles traverse the interface entering the inner phase, which breaks the interface resulting in emulsion coalescence. Hence, monodispersed particles more wetted by the inner phase of droplets are preferred as the destabilizers. Overall, this research helps gain the understanding of particles at oil-water interface and expands the application of solid particles in the stabilization and destabilisation of emulsions.
Supervisor: Binks, Bernard P. Sponsor: China Scholarship Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Chemistry