Visible light induced bending and unbending behavior of crosslinked liquid-crystalline polymer films containing azotolane moieties

Abstract

Monodomain crosslinked liquid-crystalline polymer (CLCP) films with three crosslinking densities were prepared by thermal polymerization of the mixtures of mono and diacrylates, both of which contain azotolane chromophores. Thermodynamic properties of the monomer, the crosslinker, their mixtures and the CLCP films were determined by differential scanning calorimetry. Mesomorphic properties were studied using a polarizing optical microscope and a polarized UV-vis absorption spectrometer. Due to a longer conjugated structure of the azotolane moieties in side chains, free-standing CLCP films underwent photoinduced bending upon exposure to short-wavelength visible light at 436 nm and the bent films returned to their initial states by alternating the wavelength of the actinic visible light to 577 nm. The bending could also be induced by 530 nm visible light though the bending speed decreased with the increasing of the wavelength of the actinic light. It was also observed that the bending speed of the films was related to the order parameter, the light intensity and the temperature. The mechanical force of the films generated upon exposure to visible light at 436 nm increased with the increasing of the crosslinking density and the light intensity but decreased with the increment of the temperature.