Self-assembly Behavior And Emulsion Properties Of Amphiphilic Block Copolymer PSt-b-P(St-alt-MA)-b-PAA

In this paper, a series of ABCBA-type amphiphilic block copolymers, polystyrene-b-poly(styrene-alt-maleic anhydride)-b-polyacrylic acid (PSt-b-P(St-alt-MA)-b-PAA) with varying block ratio were successfully synthesized by reversible addition-fragmentation chain transfer radical (RAFT) polymerization using BDMAT as chain transfer agent and styrene, maleic anhydride, acrylic acid as monomers. The composition and structure of the copolymer is determined by FT-IR and 1H-NMR.The self-assembled micelles were obtained in the mixed solvents of DMF/water. The self-assembly behavior of copolymer was studied by UV-Vis tracking and laser particle sizer (LPS). Experimental results showed that hydrophilic/hydrophobic block length, initial concentration of copolymer solution and water content in selective solution would affect the self-assembly behavior. The critical water content (CWC) was lower when the copolymer hydrophilic block length and the initial concentration of copolymer solution were lower. Micelles would excessively aggregation when water content in selective solution was overhigh. PSt-b-P(St-alt-MA)-b-PAA crosslinked spherical micelles with stable structure and nanoscale, were prepared using ethanediamine as crosslinking agent. TEM, LPS and Zeta potential studies indicated that crosslinked micelles would not redissolve in good solvent, crosslinked micelles size could be larger with the appropriate increase of pH value, and the increase of salt content made micelle diameter lager and Zeta potential higher.Amphiphilic crosslinked PSt-b-P(St-alt-MA)-b-PAA micelles had been confirmed as a kind of nanoscale solid particle. Based on this, this kind of crosslinked micelles were applied to stabilize Pickering emulsion as particle emulsifier. Copolymer itself and external environment could affect the characters of crosslinked micelles, including hydrophilicity/hydrophobicity and size, etc. Therefore, these factors would play an important role on the emulsion properties of micelles. With the help of digital photos, optical microscope and conductivity meter, emulsion had been characterized. It was found that the crosslinked PSt-b-P(St-alt-MA)-b-PAA micelles could stabilize a variety of oil phases. Emulsion stability became better with micelle concentration and salt concentration increased, but too high salt concentration could make the emulsion demulsification. Emulsion stability and emulsion type could be changed by adjusting pH value of aqueous phase. By adding acid and alkali alternately, the type of emulsion could be inverted circularly. Emulsions stabilized by various crosslinked micelles with different hydrophilicity/hydrophobicity ratio exhibited disparate pH-dependence. It was confirmed by SEM that crosslinked micelle particles could stable the Pickering emulsion by attaching between oil-water interfaces.