Side-chain polysiloxane liquid crystalline elastomers from non-mesogenic components

Abstract

Synthesis and characterisation of two new azo-based polysiloxane elastomers containing non-mesogenic monomers and different cross-linkers are described. The chemical structure of the synthesised compounds was confirmed through standard analytical techniques. Remarkably, both the elastomers displayed mesophase, despite the monomer and the cross-linker being non-mesogens. The mesophase was characterised by a combination of differential scanning calorimetry, polarising optical microscopy and X-ray diffraction experiments. The X-ray diffraction studies revealed an intercalated lamellar structure for the mesophase. Interestingly, the elastomer containing biphenyl-based cross-linker showed mesophase with an extended thermal range compared to the mesophase displayed by its counterpart containing phenyl-based cross-linker. The photoisomerisation behavior of the elastomers in solution and their photoswitchable properties in the solid state have been investigated. The monodomain sample of the elastomer showed a reversible, asymmetric bending and unbending behavior upon exposure to UV and visible light respectively, with a faster response time.