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Title: Oil-dispersed pH-responsive particle as Pickering emulsifiers
Author: Zhou, Yuanyuan
ISNI:       0000 0004 6347 5820
Awarding Body: University of Leeds
Current Institution: University of Leeds
Date of Award: 2016
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In this work, the oil-dispersed polydimethylsiloxane (PDMS) sterically stabilised poly(Methl Methacrylate-2Vinyl Pyridine) p(MMA-2-VP) particles are investigated for use as Pickering emulsifiers with varied emulsification conditions (pH, particle concentrations and oil-water volume ratios) and their adsorption behaviours on 2-Dimensional curved oil-water interface. These particles are synthesised by dispersion polymerisation in dodecane and their particle content can be controlled by varying the initial MMA: 2-VP ratio (uncrosslinked particles with varied MMA-2-VP ratio in particle cores) and crosslinker concentrations (cross-linked particles with constant initial MMA-2-VP ratio). Transitional phase inversion from w/o to o/w emulsions which are stabilised by oil-dispersed p(MMA-2-VP)-PDMS particles is induced by tuning pH from 6 to 2 in aqueous phase, regardless of particle concentrations. It is the first time reported of such phase inversion in emulsions stabilised with responsive emulsifiers by responding to the relevant environmental trigger. This phenomenon occurs only in the emulsion systems that prepared in the presence of such oil-dispersed particles containing more than 62% p2-VP in cores. The particles which synthesised with 5 mol% (respect to monomer concentration) cross-linkers can stabilise most stable emulsions than others, in particular the o/w emulsion, no released oil can be observed after 10 months preparation. Pickering emulsions are also prepared by changing the oil-water volume ratio under different pHs. Catastrophic emulsion phase inversion from single emulsions to multiple emulsions are observed under certain experimental conditions, indicating that such phenomenon is not only controlled by increased dispersed phase fraction in emulsion systems but also governed by the proton concentration/quantity in aqueous phase. The o/w high internal phase emulsion gels are stabilised by such oil-dispersed pH responsive particles which synthesised with 5 mol% (respect to monomer concentration) cross-linkers at pH 2 with 70 vol% oil phase. Eventually, the measurement of interfacial tension as a function of time in the presence of varied concentrations of oil-dispersed pH responsive particles are performed basing on a pendant drop method. Oil-dispersed pH responsive particles are more interfacially active at uncharged state than charged state. The adsorption coefficient value is large at charged state (pH2) than uncharged state (pH 6), implying the fact that such particle stabilised emulsion properties are governed mainly by their adsorption kinetics.
Supervisor: Cayre, Olivier ; Hunter, Timothy ; Harbottle, David Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available