Synthesis and characterization of chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens

Abstract

A novel series of siloxane-based chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens were fabricated through synthesis involving a one-step hydrosilication reaction via a crosslinking agent containing smectic and nematic phases. The chemical properties and structures of the nematic mesogen (M₁), the chiral mesogen (M₂) and the LC crosslinking agent (CL) were carefully investigated by different analytical methods. All of the obtained side-chain liquid crystalline elastomers showed a chiral smectic phase from texture observations of POM which was confirmed by XRD analysis. The influence of CL on the phase behaviour of the chiral smectic side-chain liquid crystalline elastomers has been studied. The DSC analytical results showed that the glass transition temperatures (T_g) of the obtained elastomers increased with the gradual increase of the content of CL; while the isotropization temperatures (T_i) exhibited no remarkable changes. The thermal gravity analysis (TGA) revealed that the 5% weight loss of the decomposition temperature (T_d) was greater than 280 °C for all the obtained elastomers, meaning the thermal stability of the elastomers was good. The fourier transform infrared (FT-IR) imaging system showed that the molecular distribution of the elastomers was relatively even. The effective crosslinking density of the elastomers was characterized by swelling experiments showing that the molecular weight between the crosslinking points decreases with an increase of the CL.