Brief overview on²H NMR studies of polysiloxane‐based side‐chain nematic elastomers

Abstract

This is a brief overview on recent studies on liquid crystalline elastomers (LCEs) based on polysiloxane chain, in the form of monodomain films, selectively (2)H-labeled in different parts of the LCE samples, i.e. on the crosslinker or mesogenic units. (2)H NMR spectroscopic techniques were used to measure the temperature dependence of the quadrupolar splittings, line widths and relaxation times, T(1) and T(2). From these data, several information about the orientational order parameter, S, of various LCE fragments, thermodynamic features of the isotropic-nematic transition and main motional processes could be generalized for this type of elastomers.

Nanostructured Composites Based on Liquid-Crystalline Elastomers

“…An important aspect of these LCE-based systems is related to the degree of orientational order as the temperature is varied from T > T N-PN to room temperature and vice versa. Deuteron ( 2 H) NMR studies of selectively labeled LCE and LCE-based composites were of help in deeply investigating this aspect [21,60,69,70,71,72,73,74]. The temperature dependence of the measured 2 H NMR spectra, and the trends of the quadrupolar splitting can be analyzed to obtain the local orientational-order parameter, S(T) , which indicates the average degree of order of the principal mesophase director ( n ).…”

New Liquid Crystalline Elastomeric Films Containing a Smectic Crosslinker: Chemical and Physical Properties

“…The interest in new LCE-based materials related to their rich variety of applications is a great stimulus also for the development of physical models at the meso-scale [8,[45][46][47] and for the better understanding of these systems at the molecular and supramolecular scale [15][16][17][18][48][49][50][51]. In this regard, several experimental techniques, such as Deuterium Nuclear Magnetic Resonance ( 2 H NMR), are successfully applied to LCEs selectively labelled by deuterium in different positions (crosslinkers or comonomers) [18,33,[52][53][54][55][56] or doped with small deuterated probes [57][58][59][60]. Static 2 H NMR experiments are helpful for elucidating the nature of the isotropic (Iso) to mesophase transition [61,62], which in most of the cases is a nematic phase, while in much less of the cases is a smectic phase [11][12][13][14].…”

Self-Jumping of a Liquid Crystal Elastomer Balloon under Steady Illumination

“…Among the different stimuli, light is the most favorable stimulus, which has the unique advantages of sustainability, precise controllability, and contactless driving [ 51 , 52 ]. As an important optically responsive material, the liquid crystal elastomer is synthesized by a composition of rodlike mesogenic monomers and backbones or side chains of flexible cross-linked polymers, and it combines rubber elasticity with liquid crystalline anisotropy to produce exceptional physical and optical properties [ 53 , 54 , 55 , 56 , 57 , 58 ]. When stimulated by external fields, such as light, heat, electricity, and magnetism, liquid crystal monomer molecules can change their configurations due to its rotation or phase transition, which induces macroscopic deformation [ 59 ].…”