Effect On Emulsion Stability And Phase Transition Ofkaolinite Modified With Vinyltrimethoxy

Pickering emulsion,as an environment-friendly emulsion,has the advantages of long stabilization period and good thermal stability.It has wide application prospects in the fields of food,cosmetics,petroleum and pharmaceutical preparation.However,Pickering particle shows a poor ability of stabilizing emulsions because of without the hydrophilic and lipophilic groups on surfaces,and is still required to cooperate with surfactant to stabilize emulsions efficiently and control the phase transition behavior.Therefore,improving the stability of Pickering emulsions and controlling the phase transition have become a hot spot of concern.Based on the structure and composition difference of kaolinite aluminium-oxygen octahedral layer and silica-oxygen tetrahedral layer,and the structure matching of aluminium hydroxyl groups of kaolinite octahedral layer and silica hydroxyl groups of vinyltrimethoxysilan(VTMS),VTMS was used to modified the octahedral surface of kaolinite for preparation emulsifiers.The kaolinite octahedral surfaces show lipophilic character after modified.Janus kaolinite with both hydrophilic and lipophilic groups on surfaces as a emulsifier were used to stabilize paraffin-water emulsions.The Janus kaolinite was characterized by fourier transformation infra-red spectra(FTIR),X-ray diffractometer(XRD),UV-Vis-NIR spectrometer(UV-vis),optical water contact angle meter,scanning electron microscopy with energy dispersive X-ray spectroscope(FSEM),and Thermogravimetric analysis(TGA).The stability and phase transition of emulsions were characterized by conductivity analyzer,viscometer,optical microscope,and laser particle size analyzer.The main conclusions are presented as follows:The aluminium hydroxyl groups of kaolinite octahedral surface were grafted with the silicon hydroxyl groups of hydrolyzed VTMS.Janus characteristics of kaolinite was enhanced by selective modification.Temperature played a key role for modification of kaolinite.The wettbility of Janus kaolinite could be adjusted by controlling temperature.In the range of 40~80 oC,Janus kaolinite was with a contact angle of 93o~170o,a thermal degradation temperature of 180~300 oC.Janus kaolinite shown a good performance on stabilizing emulsions.The wettbility of Janus kaolinite had an effect on the stability of emulsions,demulsification phenomenon was not observed after standing 90 days..The final volume fraction of emulsions stabilized by Janus kaolinite modified at temperature of 40 oC was 87% and the droplet of emulsion dispersed phase was with an diameter of 125 μm.The final volume fraction of emulsions stabilized by Janus kaolinite modified at temperature of 70 oC was 80% and the droplet of emulsion dispersed phase was in even distribution with an average diameter of 20 μm.The emulsions phase transition could be controlled through adjusting the wettbility of Janus kaolinite or the initial oil volume fraction.Janus kaolinite modified at temperature of 40~50 oC could stabilize oil-in-water(O/W)emulsions,Janus kaolinite modified at temperature of 74~80 oC could stabilize water-in-oil(W/O)emulsions.Janus kaolinite modified at temperature of 60~70 oC could stabilize different type of emulsions,including O/W emulsions,W/O emulsions,water-in-oil-in-water(W/O/W)emulsions.The viscosity of O/W emulsions nearby phase transition reaching the maximum.Specifically,emulsions stabilized by Janus kaolinite modified at 67 oC shown triple or double phase transition of O/W→W/O→O/W→W/O at the initial oil volume fraction of 0.20,0.27,0.53,respectively;emulsions stabilized by Janus kaolinite modified at 70 oC shown double phase transition of W/O→O/W→W/O at the initial oil volume fraction of 0.30,0.43.