Dual pH- and Light-Responsive Amphiphilic Random Copolymer Nanomicelles as Particulate Emulsifiers to Stabilize the Oil/Water Interface

Dual pH- and light-responsive nanomicelles self-assembled from amphiphilic random poly­(methacrylic acid-co-methyl methacrylate-co-7-(4-vinylbenzyloxyl)-4-methylcoumarin) (P­(MAA-co-MMA-co-VM)) have been successfully prepared and employed as particulate emulsifiers to stabilize the oil/water interface. The self-assembling behavior of copolymers in a selective solvent is explored. The structural transitions of CP55 micelles based on a copolymer with 55 mol % hydrophilic methacrylic acid units are investigated by the dosage of ultraviolet irradiation and pH variation. As pH increases, the ionization of the carboxyl groups leads to the swelling of micelles. Both the size and polydispersity index of cross-linked micelles are far larger than those of un-cross-linked micelles under alkaline conditions. The comparison of the configuration of the un-cross-linked micelles and cross-linked micelles at the oil/water interface is investigated by scanning electron microscopy. The results show that the ability of swelling and conformational changing in response to external pH- and light-triggers largely affected the emulsifying performance of the particulate emulsifiers. Especially for emulsions stabilized by the cross-linked micelles, oil begins to separate out as pH elevated over 7.3 on account of the restricted conformational adjustment that resulted from the increasing interparticle cross-linking and electrostatic repulsion. The findings may be useful for challenging industrial areas where organic macromolecules and surfactants cooperate.