Multiresponsive Azobenzene-Modified Microgels with Polyampholyte Behavior

Multiresponsive microgels that are able to respond to different stimuli are essential for the development of complex soft matter systems. Here, light, temperature, and pH-multiresponsive microgels were successfully fabricated via mAzo post-modification on the prepared poly(N-vinylcaprolactam-co-acrylic acid) microgels. The synthesized mAzo-modified microgels exhibit reversible photoswitching behavior upon blue, green or red light irradiation, and light triggers size change, as a result of the trans–cis isomerization induced by different visible light irradiations. The synthesized microgels also exhibit temperature responsiveness reflected by the temperature-induced change of hydrodynamic radius, and the incorporated hydrophobic mAzo units contribute to shifts to lower values of the volume phase transition temperature (VPTT) of the microgels. Importantly, the mAzo-modified microgels demonstrate a charge reversal behavior, and a "V"-shaped trend of size change from pH 4 to pH 10 was obtained because of the existence of mAzo moieties and carboxyl groups in the microgels.