Orientation of Azobenzene Mesogens in Side-Chain Liquid Crystalline Polymers: Interplay between Effects of Mechanical Stretching, Photoisomerization and Thermal Annealing

The interplay of the mechanically and optically induced orientation of azobenzene mesogens as well as the effect of thermal annealing was investigated for both a side-chain liquid crystalline polymer (SCLCP) and a diblock copolymer comprising two SCLCPs bearing azobenzene and biphenyl mesogens, respectively. Typically, the polymer film was first subjected to stretching in either nematic or smectic phase to yield orientation of azobenzene mesogens either parallel or perpendicular to the strain direction, then exposed to unpolarized UV light to erase the mechanically induced orientation upon the trans–cis isomerization, followed by linearly polarized visible light for photoinduced reorientation as a result of the cis–trans backisomerization, and finally heated to different liquid crystalline phases for thermal annealing. The change in orientation was monitored by means of infrared dichroism. The results have unveiled complex and different orientational behaviors for the homopolymer of poly{6-[4-(4-methoxyph...