We report on a multiresponsive emulsion stabilization/breaking by hydrogen-bonded polymer complexes of poly(methacrylic acid) (PMAA) and poly(N-isopropylacrylamide) (PNIPAM). Unlike their comprising polymers, hydrogen-bonded complexes could stabilize emulsions at acidic pH and ambient temperature. The stabilization of emulsions was dependent on the ratio of PNIPAM to PMAA and could be reversed by increasing pH and/or temperature. The use of PMAA tagged with a covalently attached Alexa-488 fluorophore (PMAA*) enabled further investigation of the interfacial complex formation using fluorescence microscopy and fluorescence correlation spectroscopy (FCS). These studies indicated that PNIPAM/PMAA* complexes were formed at liquid-liquid interfaces in a wider pH range than they did in the bulk and selectively existed at liquid-liquid interfaces at pH values between 5 and 6. FCS measurements of the molecular mobility of PNIPAM/PMAA* complexes indicated slow interfacial dynamics. Fourier transform infrared spectroscopy (FTIR) revealed that the degree of ionization of PMAA within interfacial complexes was significantly lower than within complexes formed in bulk solution at the same pH. This work presents the first example of reconfigurable, interface-assembled amphiphiles for efficient control of the stability of liquid-liquid interfaces using multiple stimuli.

Interfacial assembly of hydrogen-bonded complexes for stimuli-responsive emulsion stabilization and breaking

254th National Meeting (2017)

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