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

ABSTRACT

Several 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.

Graphical Abstract

KEYWORDS:

• Liquid crystalline elastomer
• NMR
• mesogen
• cross-linker
• dynamic
• liquid crystals
• artificial muscles
• soft actuators

Acknowledgements

V. D. thanks Jozef Stefan Institute for hosting her as visitor professor.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This research was partially supported by the research project CSF 16-12150S and COST Action 1208 (Integrating devices and materials: a challenge for new instrumentation in ICT).