Emulsion Stabilized By Stimuli-Responsive Emulsifiers Based On Dynamic Covalent Bonds

Emulsions are a class of disperse systems consisting of two immiscible liquids.The formation and the deemulsification of the responsive emulsions can be controlled by some external stimuli,such as temperature,p H,and ion strength etc.The responsive emulsions have many important applications in many fields,like oil recovery,and interface reaction,and so on.In this thesis,stimuli–responsive emulsions stabilized by emulsifiers fabricated by B-O reversible covalent bonds were reported,and the detailed contents included the following two parts:(1)Dual responsive Pickering emulsions stabilized by the constructed core crosslinked polymer nanoparticles via reversible covalent bonds.Firstly,well-defined poly(N,N-dimethylacrylamide)-b-poly(3-acrylamidophenylboronic acid)(PDMA-b-PAPBA)diblock copolymers were synthesized by sequential reversible addition-fragmentation chain transfer(RAFT)polymerization reactions.By means of the complex of PBA units in PDMA-b-PAPBA with PVA in basic water,core crosslinked polymer nanoparticles(CCPNs)with a core-shell structure were formed.The PAPBA/PVA crosslinked network and PDMA acted as the core and shell,respectively.Because of the reversible B-O chemical bonds in the core,the as-produced CCPNs showed structure transitions in response to the external stimuli involving p H and glucose.The investigation on the interfacial activities revealed that CCPNs exhibited high emulsifying performances,and oil in water(o/w)Pickering emulsions could be formed at a low particle content.The formed Pickering emulsion showed a high stability at room temperature without any disturbances,whereas deemulsification was observed upon improving p H or adding the glucose at a given p H.(2)Dual responsive emulsions that were stabilized by amphiphilic dynamic graft copolymers formed in-situ at the oil-water interface.Firstly,linear poly(N,N-dimethylacrylmide)-ran-poly(3-acrylamidophenylboronic acid)(PDMA-ran-PAPBA)copolymers with phenylboronic acid lateral groups copolymers and linear polystyrene with bihydroxyl terminal(PS(OH)2)polymers were synthesized separately by reversible addition-fragmentation chain transfer(RAFT)polymerization reaction.And then,the water containing PDMA-ran-PAPBA copolymers and the toluene containing PS(OH)2 were used as the water phase and the oil phase,respectively,and oil in water emulsions were formed by the homogenization.The dispersed oil droplets were stabilized by the amphiphilic PDMA-ran-PAPBA-g-PS graft copolymers,which were formed in-situ at the oil-water interface during the homogenization by means of the complexation of lateral PBA units of PDMA-ran-PAPBA with the diol terminals of PS.Owing to the reversible B-O chemical bonds,the grafted PS side chains could be detached by the decreasing of p H or the addition of the glucose,and this conferred the generated oil in water emulsions with p H-and glucose-induced deemulsification features.