Fabricating switchable Pickering emulsions by dynamic covalent copolymer amphiphiles

Abstract

In this work, amphiphilic copolymers D-An based on the dynamic imine bonds were generated in-situ in the aqueous solutions by two water-soluble precursors, the random copolymer poly(N-(2-methacryloylxyethyl)-random-poly(4-(formaldehyde) phenyl methacrylate) (PNMP83-co-PBFMA4, Precursor D) and alkylamines (Precursor An, n represents the carbon number in the alkyl chain that is ranging from 4 to 10). Amphiphiles D-An formed micelles spontaneously in the aqueous solutions, which were studied by the surface tension and cryogen-transmission electron microscopy (cryo-TEM) measurements. Moreover, the CO2/N2 responsive micellization of D-An due to the reversible formation and breaking of the dynamic imine bond (-CH=N-) was confirmed by the nuclear magnetic resonance (NMR) measurements. Accordingly, the emulsification of dynamic covalent amphiphilic copolymers D-An was studied in detail. O/W Pickering emulsions with excellent stability were commonly generated by employing D-An as emulsifiers regardless of n and the nature of oil employed, which was significantly different from the weak emulsification of either precursor D or precursor An. The synergistic emulsification of D-An monomers and micelles was proved to be the major cause as evidenced by the confocal laser scanning microscopy (CLSM) method. Noticeably, the abundant alkylamines were also advantageous in stabilizing emulsions. Attributing to the stimuli-responses of amphiphiles D-An to CO2/N2, the stability of Pickering emulsions could be reversibly controlled by CO2/N2 as well.