Investigation And Applications Of Pickering Emulsions Prepared By Phase Inversion

Emulsions and Pickering emulsions play important roles in the fields of drug delivery,tissue engineering,oil exploitation and water treatment,etc.When the emulsions complete their intended functions,the separation of the oil and water is usually needed.Therefore,the controllable emulsification-demulsification and transformation between emulsion types are widely concerned in applications.Based on the phase inversion principle of emulsions,my thesis constructed two systems to realize the emulsion phase inversion by applying metal ion stimulation or changing particle wettability.The systems can be used for extraction and separation of rare earth ions in wastewater and preparation of bicontinuous interfacially jammed emulsion gel(Bijel),thus broadening the applications of emulsion phase inversion and greatly simplifying the construction method.The thesis mainly consists of three parts.Chapter Ⅰ:The basic concepts of emulsions and Pickering emulsions,the classification and function of stabilizers of emulsions are introduced;the preparation methods and applications of the Bijel are summarized,as well as the principle and strategy of realizing the phase inversion of Pickering emulsions are described.By summarizing the previous studies,the research contents,purpose and significance of this thesis are introduced.Chapter Ⅱ:Metal ion-triggered Pickering emulsions for extracting and separating rare earth ions were discussed.The metal ion extractant,2-ethylhexyl phosphoric acid mono-2ethylhexyl ester(EHEHPA),could be deprotonated into an anionic surfactant,EHEHP",causing the emulsification of EHEHPA/H2O system to form O/W emulsions or EHEHP" solutions according to the different protonated degrees.When the O/W emulsion stabilized by EHEHP"met with some multi-valent metal ions,the insoluble(EHEHP)nM particles were generated,realizing the in-situ transformation from emulsions to Pickering emulsions,or from EHEHP"solution to Pickering foams,with the results of selectively extracting some rare earth ions.By tuning pH,the extraction agent,EHEHPA,can be effectively recovered by demulsifying or defoaming the Pickering emulsions or foams.In this work,EHEHPA can act as oil,anionic surfactant and surface-active particles at different forms,achieving the convenient and reversible transformation between different dispersion states.This work avoids the additional surfactants,being hopeful to provide useful understanding for constructing emulsions or foams in an unusual consideration.Chapter Ⅲ:Bijel was constructed based on Pickering emulsion phase inversion principle.The surface wettability of cellulose nanocrystalline particles(CNC)was changed by in-situ binding of hydrophilic CNC with mixed molecular weights of hydrophobic poly(dimethylsiloxane)etherimide(PDMS-NH2),acting as the stabilizers locating at the oil-water interface.The Pickering emulsions realized O/W-Bijel-W/O transition with the changing ratio of CNC and PDMS-NH2.By direct mixing method at the appropriate ratio range,Bijel was successfully constructed at room temperature,which greatly simplified the construction process,being conducive to large-scale preparation and applications of Bijel.