Stimuli-Responsive Pickering Emulsions:Preparation And Apllication

Pickering emulsion is a dispersed system stabilized by solid particles instead of low molecular weight surfacants.Pickering emulsion has been widely used in the fields of crude oil extraction,interface reaction,materials synthesis,etc.due to its good stability,tunable droplet size and low toxicity.The high stability of Pickering emulsion is of importance in industry.However,in some cases where only the temporary stability is required,such as interfacial reaction and oil transportation,etc,stimuli-responsive Pickering emulsions integrating the high stability with on-demand demulsification are much desired.It is particularly important to prepare particles with high emulsifying performances and stimuli-responsive interfacial activities.Polymerization induced self-assembly(PISA)has become a powerful technique for a scalable preparation of polymer nanoparticles with various morphologies.To date,a large number of diblock copolymer nanoparticles with different morphologies(sphere,worm,vesicle,lamella,etc)have been yielded via PISA formulations.Compared with the spherical structures,anisotropic polymer worms displaying extremely excellent emulsifying performances.The main contents of this thesis were summarized as follows:(1)Preparation of temperature/pH-responsive Pickering emulsion.POEGMA-b-PDAAM diblock copolymer nanoparticles with different morphologies,including sphere,worm,vesicle,etc,were synthesized via RAFT-mediated aqueous dispersion polymerization using POEGMA and PDAAM stabilizer block and core-forimg block,respectively.The factors influencing the morphologies of polymer nanoparticles,such as the length of stabilizer block and the solid content,were carefully investigated.The morphological transitions of POEGMA-b-PDAAM diblock copolymer nanoparticles with advanced morphologies in response to pH and temperature were studied.POEGMA-b-PDAAM diblock copolymer nanoparticles were employed as Pickering emulsifiers to prepare n-dodecane-in-water Pickering emulsions.Compared with spherical and vesicular counterparts,POEGMA-b-PDAAM worms exhibited the best excellent emulsifying performances.The responsive demulsifying of n-dodecane-in-water Pickering emulsions stabilized by POEGMA-b-PDAAM worms were studied in detail.And the results revealed the Pickering emulsions demonstrated a slow demulsification at pH10 or 70 ~oC or pH10/70 ~oC combinations,and a long time(～2-7 hours)were needed for the total demulsification,whereas a rapid demulsification(within 10 min)was achieved at 90~oC.The different demulsification rates were attributed to different sensitivities of POEGMA shells and PDAAM cores of POEGMA-b-PDAAM worms to external stimuli.(2)pH-responsive Pickering emulsions:preparation and interfacial catalytic applications.:Preparation and application as a highly efficienct and recyclable.platform for adol reaction PEO-b-PGMA diblock copolymer nanoparticles with different morphologies,including sphere,worm,vesicle,etc,were synthesized via photo-mediated RAFT dispersion polymerization in water/ethanol mixure using PEO and PGMA stabilizer block and core-forimg block,respectively.The PGMA cores of PEO-b-PGMA worms were further chemically cross-linked using ethylenediamine as the cross-linkers.It was revealed that core cross-linked PEO-b-PGMA worms exhibited excellent emulsifying performances in netural or alkalic surroundings,which could be used as stabilizers for the formation of n-decane-in-water Pickering emulsions at a low content.However,n-decane-in-water Pickering emulsions stabilized by core cross-linked PEO-b-PGMA worms displayed demulsifying at acidic surroundings.The demulsifying rate was related to pH,and rapid demulsifying was achieved at a low pH.Such pH-responsive n-decane-in-water Pickering emulsions provided a readily platform for the adol reaction between benzaldehyde and acetone catalyzed by alkali.The reaction kinetic was investigated.