Pickering emulsification of pyrrolidone-based block copolymer aggregates: Effects of copolymer composition and oil

A series of block copolymers poly ( N -2-(methacryloyloxy) ethyl pyrrolidone)- b -poly (benzylmethacrylate) (PNMP 39 - b -PBzMA n ) were developed. These amphiphilic copolymers formed diversified aggregates in water, depending on the degree of polymerization n of the PBzMA segment. There presented the n -induced morphological transition from spherical micelles to vesicles via wormlike micelles. Moreover, PNMP 39 - b -PBzMA n aggregates were excellent dual function emulsifiers, showing similarity with both particles and surfactants simultaneously. The emulsification of PNMP 39 - b -PBzMA n aggregates was affected significantly by the degree of polymerization n of the PBzMA segment and oil. However, the effect of oil was more remarkable in comparison with that of n , in which the compatibility between oil and the hydrophobic PBzMA segment was critical. In general, O/W and W/O emulsions were formed for oils with poor and good compatibility to the PBzMA segment such as nonpolar alkanes and toluene, respectively. In these cases, PNMP 39 - b -PBzMA n aggregates were remained in water in the alkane/water systems, whereas they were transferred into the toluene phase according to the similarity-intermiscibility principle. For isopropyl myristate, a polar oil with the intermediate compatibility to the PBzMA segment, PNMP 39 - b -PBzMA n in water were transferred into the oil phase partially. Accordingly, emulsifiers in water and oil benefit the formation of O/W and W/O emulsions, respectively, as observed in the alkane/water and toluene/water systems. As a result, O/W and W/O emulsions were generated by PNMP 39 - b -PBzMA n with relatively small and large n , respectively. For PNMP 39 - b -PBzMA n with the intermediate n , W/O/W multiple emulsions were formed attributing to the synergistic emulsification of PNMP 39 - b -PBzMA n in water and oil.