Size-dependent light-driven effect observed for azo polymer colloidal spheres with different average diameters.
In this work, colloidal spheres with different average diameters were prepared by using azo polymers (BP-AZ-CA and BP-AZ-NT) and photoinduced deformation behavior of the colloidal spheres was studied. The colloidal spheres were prepared through gradual hydrophobic aggregation of the polymeric chains in THF/H2O media and characterized by using transmission electron microscopy, dynamic light scattering, and UV-vis spectroscopy. The colloidal spheres with different average diameters were obtained by adjusting the polymer concentration and water-adding rate in the preparation processes. The photoinduced deformation behavior was studied by irradiating the colloidal spheres in the solid state with a linearly polarized Ar+ laser beam (488 nm, 80 mW/cm2). Upon being irradiated with light, the colloidal spheres were elongated along the polarization direction of the laser beam. Results show that the deformation rate, maximum deformation degree, and even deformed shape are closely related to the average diameters of the colloidal spheres. Under the same light irradiation condition, the colloidal spheres with average diameters in the range of 200-300 nm show the fastest deformation rate and largest deformation degree among the series. For colloids similar in size, the BP-AZ-CA colloidal spheres exhibit deformation rates significantly faster than those of the BP-AZ-NT colloidal spheres. The BP-AZ-CA colloidal spheres with an average diameter of 510 nm show more complicated "spindle-like" or "tadpole-like" shapes after light irradiation for 45-85 min. These results clearly indicate that the photoinduced deformation behavior is significantly dependent on the sizes of the colloidal spheres. The observation can shed some new light on the possible mechanism of the photoinduced colloid deformation.
Department of Chemical Engineering, Laboratory for Advanced Materials, Tsinghua University, Beijing, P. R. China 100084.
Junpeng
J
Liu
Yaning
Y
He
Xiaogong
X
Wang