Azo polymer colloidal spheres containing different amounts of functional groups and their photoinduced deformation...

In this work, colloidal spheres composed of azo polymers with different chromophore loading densities were prepared, and their photoinduced deformation behavior was studied. The colloids were constructed by using a series of amphiphilic epoxy-based random copolymers containing 4-carboxylazobenzene functional groups with different degrees of functionalization (DFs). The colloidal spheres were fabricated through gradual hydrophobic aggregation of the polymeric chains in tetrahydrofuran-H2O dispersion media, which was induced by gradually adding water into the systems. The colloidal spheres were characterized by using transmission electron microscopy and dynamic light scattering. The photoinduced deformation behavior was studied by irradiating the colloidal spheres with a linearly polarized Ar+ laser beam. Results showed that the critical water content (CWC) for the colloid formation is related to the DF of the polymers, and CWC increases with the increase of DF. The hydrodynamic diameter of the colloidal spheres is also related to the DF of the polymers. When the DF of the polymers increases, the average size of the colloids gradually decreases. The hydrodynamic diameter of the colloidal spheres increases as the water dropping rate decreases. When the dropping rate is below 20 microL/s, the size of the colloidal spheres increases abruptly as the dropping rate further decreases. Upon the linearly polarized Ar+ laser beam irradiation, the colloids composed of polymers with different DFs can all be elongated along the polarization direction of the laser beam. As DF increases, the deformation degree characterized by the axial ratio (l/d) almost linearly increases. These observations can give some insight into the photoinduced deformation mechanism and can be used to construct colloids with different sizes and photoresponsive ability.