Hybrid Colloids Composed of Two Amphiphilic Azo Polymers:  Fabrication, Characterization, and Photoresponsive Properties.

This article reports the fabrication and characterization of a novel type photoresponsive colloids composed of two amphiphilic azo polymers. The colloids were built up by using an amphiphilic random azo copolymer (PEAPE) and a polydispersed azo homopolymer (BP-AZ-CA), which were functionalized with azobenzene type and pseudo-stilbene type chromophores, respectively. The colloids were prepared by gradually adding deionized water into a THF solution containing both PEAPE and BP-AZ-CA. In order to study the influence of the preparation conditions on the colloid composition and structure, the colloids were also prepared by mixing two THF−H2O solutions or dispersions of the polymers with different initial water content (Cw0) and then adding water into the mixture. When mixing the solutions with Cw0below the critical water content (CWC), uniform colloidal spheres composed of the two polymers could be obtained. Upon irradiation of a linearly polarized Arlaser beam, the hybrid colloidal spheres were deformed to “tadpole-like”, “spindle-like”, and other nonspherical structures depending on the composition of the colloids. As only the BP-AZ-CA component could be driven by the light irradiation, the photoinduced deformation degree increased with the increase of the active component in the hybrid colloids. When mixing the dispersions with Cw0above CWC, the colloids obtained were observed to be a mixture of the hybrid colloids and monocomponent colloids. The photoisomerization study confirmed that the cores of the hybrid colloids were formed from the more hydrophobic PEAPE component, and the coronas were rich in the BP-AZ-CA component. The colloidal structures were formed due to the gradual hydrophobic aggregation of the polymeric chains in the THF-H2O media. In the forming process, the more hydrophobic PEAPE chains started to aggregate first and then BP-AZ-CA chains gradually assembled on the cores while the water content gradually increased. The understanding and methodology can be applied to construct colloids composed of two or more photoresponsive polymers or even other functional polymers. [ABSTRACT FROM AUTHOR]