Ruoyuan Yin

NIR-light-induced deformation of cross-linked liquid-crystal polymers using upconversion nanophosphors.

When upconversion nanophosphors were incorporated into an azotolane-containing cross-linked liquid-crystal polymer film, the resulting composite film generated fast bending upon exposure to continuous-wave near-IR light at 980 nm. This occurs because the upconversion luminescence of the nanophosphors leads to trans-cis photoisomerization of the azotolane units and an alignment change of the mesogens. The bent film completely reverted to the initial flat state after the light source was removed.

Can sunlight drive the photoinduced bending of polymer films

Photoinduced bending and unbending behavior of crosslinked liquid-crystalline polymers containing azotolane moieties in side chains occurred upon irradiation with sunlight, according to the trans–cisphotoisomerization of the azotolane moieties.

Photoinduced bending behavior of crosslinked liquid-crystalline polymer films with a long spacer

An acrylate monomer and diacrylate crosslinker containing a spacer of undecylene were synthesized and crosslinked liquid-crystalline polymer films with different crosslinking densities were prepared by photopolymerization of mixtures of the monomer and the crosslinker. Due to the relatively long spacer, distinct bending behavior was observed in the film with a low crosslinking density: when the temperature was lower than 90 °C, the film first bent away from the light source and then towards it upon the irradiation of UV light. As the temperature was raised above 90 °C, the film bent directly towards the light source. X-ray diffraction was used to probe the phase structures of the film at different temperatures and a plausible mechanism was presented to explain the distinct phenomenon. In addition, when the crosslinking density was increased, all the films bent directly towards the light source with faster speed, which is related to their modulus and order parameters.

NIR-Light-Driven Soft Actuation Materials Based on Crosslinked Liquid-Crystalline Polymers

Two kinds of composite films were obtained by incorporating upconversion nanophosphors into monodomain and polydomain crosslinked liquid crystalline polymer films containing azotolane moieties. When exposure to continuous-wave near-infrared light at 980 nm, the monodomain composite film generated fast bending along the rubbing direction of the polyimide alignment layers, whereas the bending direction of the polydomain composite film was random. The anisotropic effect of the azotolane mesogens on the deformation and the measurement of thermal effect indicate that the bending is caused by the means of photochemistry rather than the thermal effect of NIR light; that is, the upconversion luminescence of the nanophosphors leads to trans−cis photoisomerization of the azotolane units and the alignment change of the mesogens.

Preparation and Characterization of Crosslinked Liquid-Crystalline Polymer Films with a Long Spacer

Three azobenzene acrylate monomers containing alkyl spacers of different length were synthesized. Thermodynamic and mesomorphic properties of the monomers were measured by differential scanning calorimetry and polarizing optical microscopy. A crosslinker with the undecyl spacer was also synthesized to prepare crosslinked liquid-crystalline polymer films by photopolymerization. Polarized UV spectra and polarizing optical micrographs demonstrated that the mesogens are aligned homogeneously in the films. Low glass transition temperature of the films enabled them to bend near room temperature upon UV irradiation. Besides, the films generally bent away from the light source before they at last bent towards the light irradiation.

Light-Driven Soft Actuator Materials Based on Liquid-Crystalline Polymers

Various kinds of crosslinked liquid-crystalline polymers were synthesized with acrylate monomers and diacrylate cross-linkers containing azobenzene moieties. The effect of spacer length on photoinduced bending behavior of the polymer films was investigated. The films with long spacers exhibited low glass transition temperatures and underwent bending and unbending behavior at room temperature. Mechanical force generated during the process of UV light irradiation was also measured. It was found that the maximum force increased with the increment of the cross-linking density and the intensity of UV light.