Paranematic–nematic phase transition in liquid crystalline elastomers: a²H-NMR study

Abstract

In this study, selectively deuterium-labelled monodomain liquid single crystalline elastomers have been investigated by means of 2 H-NMR spectroscopy. The analysis of the spectral features as well as the study of the orientational properties in the paranematic and nematic phases confirmed the supercriticality of the paranematic-nematic transition as an intrinsic property of these systems. Moreover, the combined study of the spin-spin relaxation times (T 2 ) and the 2 H-NMR spectral linewidth measured in the paranematic phase indicates the presence of slow dynamic motions.

Recent NMR Studies of Thermotropic Liquid Crystals

“…DNMR studies of selectively deuterated crosslinkers in side-chain LSCE monodomain films have recently confirmed the criticality of the PN-N phase transition being an intrinsic property of LSCE systems [325]. Some studies of deuterium T 1Z and T 2 relaxation time measurements have also been reported on LSCE samples [326,327]. Most DNMR studies of selectively deuterated LSCEs show broader spectra in samples containing deuterated crosslinkers [325,327] versus deuterated mesogens [326,328] or doped LSCEs [329].…”

“…Some studies of deuterium T 1Z and T 2 relaxation time measurements have also been reported on LSCE samples [326,327]. Most DNMR studies of selectively deuterated LSCEs show broader spectra in samples containing deuterated crosslinkers [325,327] versus deuterated mesogens [326,328] or doped LSCEs [329]. Measurements and analyses of T 2 relaxation times in the I (PN) and N phases have been done on LSCE films containing deuterated crosslinkers.…”

The role of NMR in the study of partially ordered materials: Perspectives and challenges

“…These investigations successfully showed the fundamental role of crosslinker density in determining the thermodynamic features of the paranematic-nematic phase transition (PN-N) [80,81]. Recent 2 H NMR studies of side-chain LSCE monodomain films selectively deuterated on the crosslinker were published [213,214], confirming the criticality of the PN-N phase transition as an intrinsic property of LSCE monodomain systems. Since the particular two-step crosslinking reaction [213] is considered the "key-point" of the shape-memory properties of LSCEs, a detailed study was performed on several LSCE films 2 H-labeled on the crosslinker, as reported in Fig.…”

Bending actuation of a composite liquid crystal elastomer via direct Joule heating

“…In order to overcome these problems we present here a bilayered composite material in which the conductive surface layer is produced adding on the surface of a monodomain nematic LCE (based on a poly-siloxane backbone with chemical composition as in [6]) a thin conductive polymer layer. Coupling of the two layers was achieved by drop casting a waterborne solution of the conductive polymer poly(ethylenedioxythiophene):…”