Fabrication of re-shapeable liquid crystalline elastomers with dynamic C–N bonds and investigation of their reversible photoresponsive bending behaviors

Abstract

<p indent=0mm>Liquid crystalline elastomers (LCEs) spontaneously change their dimensions and shapes in response to external stimuli, such as heat or light irradiation; however, LCEs based on conventional covalent crosslinks are thermosetting materials and thus unable to remold or fabricate into complex three-dimensional (3D) soft actuators. In this work, we prepared polysiloxane side-chain liquid crystalline polymers with both <italic>p</italic>-methoxyphenyl benzoate (PB) and azobenzene (Azo) mesogens introduced as side groups through thiol-ene click reaction. Then a monodomain liquid crystalline elastomer LCE-M film was fabricated by fixing the macroscopic alignment of mesogens induced by uniaxial stretching upon heating to a higher temperature through C–N dynamic covalent bonds via highly efficient transalkylation between alkyl bromide and triazole from azide-alkyne click reaction to achieve rearrangement and regeneration of the crosslinked networks. The introduction of Azo mesogen with <italic>trans</italic>-<italic>cis</italic> isomerization characteristics endowed the LCE-M thin films with reversible photoresponsive deformation properties of bending-stretching recovery upon alternate irradiation of UV and visible light. With the separation of alignment method and driving mode of such liquid crystalline elastomer material, the monodomain liquid crystalline elastomer LCE-M thin films can be repeatedly and stably driven by light irradiation at room temperature, which is expected to be employed for the fabrication of reshapeable flexible LCE actuators with faster photo response.