Preparation And Application Of Amphiphilic Block Copolymer Modified Silica Nanoparticles

Stimuli-responsive(including thermosensitive and pH responsive) polymer/silica nanoparticles can be prepared via silica modification with functional polymers. Amphiphilic block copolymer endows silica nanoparticle the same amphiphilic properties which shows significant advantages in stabilizing Pickering emulsion. Yet, few reports concerns on silica nanoparticles modified with amphiphilic block copolymer, even the appliance in Pickering emulsion. In this study, our main work focus on preparation of amphiphilic block copolymer modified silica nanoparticles and its application in Pickering emulsion, the main contents and results are listed as follows:First, amphiphilic ABC 3-miktoarm terpolymer consisting of hydrophilic poly(ethylene glycol) monomethyl ether(PEG), hydrophobic polystyrene(PS) and cross-linkable poly(3-(3-(Triisopropyloxysilyl)propyl methacrylate)(PIPSMA) were synthesized by combination of atom transfer radical polymerization(ATRP) and click chemistry. The polymers were well defined through 1H NMR and GPC characterization.Second, amphiphilic block copolymer μ-(PEG45-b-PS25-b-PIPSMA25) grafted silica nanoparticle was prepared through sol-gel method. Influence of coating solvent, catalysts and reaction time on the graft density were investigated. The polymer/silica nanoparticles were well defined through TEM, TG and IR etc. characterization and the graft density was calculated to be 0.242 chain/ nm2.At last, polymer grafted silica nanoparticles were used to stabilize Pickering emulsion. The effect of particle concentration, oil volume fraction, initial dispersion phase of modified silica and different oil type on emulsion properties were investigated, the corresponding results are listed as follows:(a) Stable Pickering emulsions can be formed between water and different oil type(cyclohexane, toluene, n-dodecane and sunflower seeds oil). And water/toluene emulsion shows a good long-term stability for more than one year;(b) Different emulsion type can be formed according to the initial dispersion phase when μ-(PEG45-b-PS25-b-PIPSMA25) grafted silica nanoparticles were used to stabilize water-to-hexane and water-tododecane emulsion. O/W emulsions can be formed when particles were first dispersed into water and W/O emulsions can be formed when particles were first dispersed into oil,and O/W/O multiple emulsion can be formed while P-silica particles were dispersed both in water and cyclohexane;(c) Stable emulsions can be formed at a very low particle concentration of 0.05%;(d) Stable water/toluene emulsions can be formed even at 20% toluene volume fraction. When toluene volume fraction decrease to 10%, a phase transition occurs and resulted in O/W emulsion. Emulsion gels were formed when toluene volume fraction rises to 30%. All these results demonstrated that amphiphilic block copolymer grafted silica nanoparticles exhibits unique properties in stabilizing Pickering emulsion.