Phototriggered Mass Migration Consorted with Surface Dewetting in Thin Films of a Liquid Crystalline Azobenzene-containing Dendrimer

Abstract

A dendritic molecule of poly(propylene imine) whose periphery is modified with photoresponsive mesogenic azobenzene units was synthesized. This compound exhibited highly ordered smectic B or smectic A layer structure orienting parallel to the substrate in the film state. When this film of 90 nm thickness on a hydrophilic substrate was exposed to UV (365 nm) light, the initial flat film morphology started to form holes followed by a drastic transformation to form separated dome structure of micrometer levels. Upon continuous UV light irradiation, the domain height increased and reached to a level of ca. 8-fold higher than that of the initial thickness, which can be correlated with the disordering of layer structures as revealed by grazing angle incidence X-ray diffraction measurements. This phototriggered dewetting behavior depended on the film thickness. The thinner film resulted in local migrations to form the smaller and more homogeneous domes. The dewetting was observed below a threshold thickness of 1...