Dynamic investigations of liquid crystalline elastomers and their constituents by 2H NMR spectroscopy

Abstract

ABSTRACTSeveral side-chain liquid single crystalline elastomers (LSCEs) were investigated by means of 2H NMR spectroscopy focusing on the temperature dependence of the spectral line width and spectral shape, as well as the T-dependence of spin–lattice and spin–spin relaxation times (T1 and T2). All measurements were performed at the Larmor frequency of 76.753 MHz for 2H. The LSCEs were prepared in the form of monodomain films by using either 2H-labelled monomers (or co-monomers), 2H-labelled cross-linkers or 2H-labelled molecular probes free to diffuse in the LSCE matrix. In all cases, deuterons are on the phenyl moiety. The main features of the measured 2H NMR properties (static and dynamic ones) in these different cases were discussed and compared with those of low-molecular-weight mesogens (i.e. the same molecules used as monomers or co-monomers in the side-chain LSCEs) in the nematic and smectic A phases. Among all investigated LSCE samples, those 2H-labelled on the cross-linker sites present distinct properties either on the 2H NMR spectral line width and spectral shape in the paranematic and in the nematic phases, which can be interpreted in terms of director reorientational dynamics in the intermediate–slow motional regime, taking into account the inherent local director misalignment of LSCEs.