²H NMR orientational study of a probe dissolved in nematic solution and, used as crosslinker, in a liquid crystalline elastomer

Abstract

The orientational order parameters, S_zz and Biax, of UB-d₄ [1,4-bis(undec-10-en-1-yloxy)benzene-d₄ ] in the ZLI1167 nematic mixture are studied by means of ²H NMR at variable temperature. The S_zz(T) trend fairly follows the Maier–Saupe theoretical curve; therefore, UB-d₄ can be considered an excellent probe to monitor the ordering of the nematic phase itself, provided that Biax is not neglected and the complete analysis of quadrupolar and dipolar splittings is performed. UB-d₄ is a typical crosslinker in liquid crystal elastomers (LCEs): the order parameters here collected help us to discuss the peculiarities of the crosslinker as a probe for the study of internal order in LCEs. From the analysis of our data and of data in the literature, we infer that the order parameter Biax of the crosslinker in the LCE matrix is low enough to be neglected without severely perturbing the determination of . The crosslinker UB-d₄ is a reliable probe to monitor the nematic order degree inside the LSCE-UB-d₄ sample.

Keywords:

• crosslinker
• liquid crystalline elastomers
• orientational order parameters
• ²H NMR

Acknowledgements

The authors thank Dr Claudia Forte of IPCF of CNR (Pisa) for supplying an amount of ZLI1167, a nematic solvent not easily available, Professor Giancarlo Galli for the hospitality in his laboratory, Dr Elisa Martinelli and Dr Sara Menghetti for help with DSC and microscopy measurements. V. Domenici and B. Zalar thank the European Commission for the EIF Marie Curie Action project No. 039643 ‘ELACEM’.