Preparation Of Pickering Emulsion With Temperature/pH Response Microgel As Emulsifier

Emulsion stabilized by colloidal particles is called Pickering emulsion.Because Pickering emulsion has many advantages such as safety,non-toxicity,and good stability.In recent years,the research on Pickering emulsion has been increasing day by day.For environmentally sensitive colloidal particle emulsifiers,the adsorption-desorption balance of colloidal particles at the oil-water interface can be achieved by adjusting the chemical substances or physical parameters of the system(such as temperature,pH,magneto-optical or gas),which is beneficial to control and adjust stability and type of Pickering emulsion.Therefore,with the deepening of the research on Pickering emulsion,the use of environmentally responsive polymer microgels as the emulsifier of Pickering emulsion has gradually become a research hotspot,providing the possibility to expand its application in the fields of medicine and food.The main purpose of this paper is to use temperature-sensitive or temperature/ pHsensitive microgels as emulsifiers of Pickering emulsions..Firstly,the soap-free emulsion polymerization method is adopted,and N-isopropylacrylamide(NIPAM)was used as the monomer,N’,N’-methylene bisacrylamide(BIS)as cross-linking agent,potassium persulfate as initiator,poly N-isopropylacrylamide(PNIPAM)microgels were prepared.Then used PNIPAM microgel as the seed,NIPAM and polyethyleneimine(PEI)as the second monomer,tert-butyl hydroperoxide(TBHP)as the initiator,and BIS as the cross-linking agent.PNIPAM/PNIPAM-PEI composite microgel PNIPAM was synthesized by seed free-soap emulsion polymerization,has a typical core-shell structure with a PNIPAM as a core and the graft copolymer of PNIPAM and PEI as a shell.Transmission electron microscopy characterization shows that the two types of microgels have submicron size and uniform spherical morphology.At different temperatures,dynamic light scattering(DLS)was used to test the fluid particle size of the two types of microgels.The test results shows that both microgels have obvious temperature sensitivity.The VPTT of PNIPAM microgel and PNIPAM/PNIPAM-PEI composite microgel are approximately 32 and 34°C,respectively.In addition,the fluid particle size of the PNIPAM/PNIPAM-PEI composite microgel decreases with the increase of the pH value of the dispersion,showing a significant pH dependence.Using toluene,trichloroethylene,n-heptane and octanol as the oil phase,the feasibility of the PNIPAM microgel and PNIPAM/PNIPAM-PEI composite microgel as the emulsifier of Pickering emulsion was explored,And systematically studied the influence of factors such as oil-water ratio,water phase particle concentration,temperature and water phase pH value on the formation of Pickering emulsion.The experimental results show that PNIPAM microgel forms a homogeneous O/W Pickering emulsions with toluene,trichloroethylene and n-heptane at 25℃,particle concentration of 1 wt% and oil / water ratio of 8:4.The formed Pickering emulsions lose its stability and are separated into oil and water phases Macroscopically when the system temperature exceeds the VPTT of the PNIPAM microgel.The PNIPAM microgel has high wettability in octanol and cannot form a stable Pickering emulsion.On the other hand,PNIPAM/PNIPAM-PEI composite microgel formed a uniform O/W Pickering emulsion with toluene at 25°C,particle concentration 1 wt%,oil-water ratio 7:5,and pH 4.