Photoresponsive anisotropic and isotropic gels of semicarbazide–azobenzene organogelators: the use of magnetic polymer colloids to detect gel–sol transformation

Abstract

Photoinduced gel–sol transformation of semicarbazide–azobenzene-based organogels containing entrapped organic solvents (isotropic gel) and liquid-crystalline material (anisotropic gel) has been studied. Thin films (4 µm) of gel materials were used to study the gel–sol transformation, as thicker films possess high absorbance due to the relatively high concentration of the gelator molecules. Photoinduced trans–cis isomerization of the azobenzene units causes destruction of the gel structure, and the consequent change in viscosity has been investigated employing magnetic polymer colloids. In the gel state the movement of the colloids is restricted due to their entrapment within the gel fibers but upon irradiation the colloids are movable and align in the direction of an external magnet, indicating collapse of the gel structure.