Brief overview on 2H NMR studies of polysiloxane-based side-chain nematic elastomers

Self-Vibration of a Liquid Crystal Elastomer Fiber-Cantilever System under Steady Illumination

A new type of self-oscillating system has been developed with the potential to expand its applications in fields such as biomedical engineering, advanced robotics, rescue operations, and military industries. This system is capable of sustaining its own motion by absorbing energy from the stable external environment without the need for an additional controller. The existing self-sustained oscillatory systems are relatively complex in structure and difficult to fabricate and control, thus limited in their implementation in practical and complex scenarios. In this paper, we creatively propose a novel light-powered liquid crystal elastomer (LCE) fiber-cantilever system that can perform self-sustained oscillation under steady illumination. Considering the well-established LCE dynamic model, beam theory, and deflection formula, the control equations for the self-oscillating system are derived to theoretically study the dynamics of self-vibration. The LCE fiber-cantilever system under steady illumination is found to exhibit two motion regimes, namely, the static and self-vibration regimes. The positive work done by the tension of the light-powered LCE fiber provides some compensation against the structural resistance from cantilever and the air damping. In addition, the influences of system parameters on self-vibration amplitude and frequency are also studied. The newly constructed light-powered LCE fiber-cantilever system in this paper has a simple structure, easy assembly/disassembly, easy preparation, and strong expandability as a one-dimensional fiber-based system. It is expected to meet the application requirements of practical complex scenarios and has important application value in fields such as autonomous robots, energy harvesters, autonomous separators, sensors, mechanical logic devices, and biomimetic design.

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

Self-oscillation capable of maintaining periodic motion upon constant stimulus has potential applications in the fields of autonomous robotics, energy-generation devices, mechano-logistic devices, sensors, and so on. Inspired by the active jumping of kangaroos and frogs in nature, we proposed a self-jumping liquid crystal elastomer (LCE) balloon under steady illumination. Based on the balloon contact model and dynamic LCE model, a nonlinear dynamic model of a self-jumping LCE balloon under steady illumination was formulated and numerically calculated by the Runge–Kutta method. The results indicated that there exist two typical motion regimes for LCE balloon under steady illumination: the static regime and the self-jumping regime. The self-jumping of LCE balloon originates from its expansion during contact with a rigid surface, and the self-jumping can be maintained by absorbing light energy to compensate for the damping dissipation. In addition, the critical conditions for triggering self-jumping and the effects of several key system parameters on its frequency and amplitude were investigated in detail. The self-jumping LCE hollow balloon with larger internal space has greater potential to carry goods or equipment, and may open a new insight into the development of mobile robotics, soft robotics, sensors, controlled drug delivery, and other miniature device applications.

Design and Self-Assembling Behaviour of Calamitic Reactive Mesogens with Lateral Methyl and Methoxy Substituents and Vinyl Terminal Group

Smart self-organising systems attract considerable attention in the scientific community. In order to control and stabilise the liquid crystalline behaviour, and hence the self-organisation, the polymerisation process can be effectively used. Mesogenic units incorporated into the backbones as functional side chains of weakly cross-linked macromolecules can become orientationally ordered. Several new calamitic reactive mesogens possessing the vinyl terminal group with varying flexible chain lengths and with/without lateral substitution by the methyl (methoxy) groups have been designed and studied. Depending on the molecular structure, namely, the type and position of the lateral substituents, the resulting materials form the nematic, the orthogonal SmA and the tilted SmC phases in a reasonably broad temperature range, and the structure of the mesophases was confirmed by X-ray diffraction experiments. The main objective of this work is to contribute to better understanding of the molecular structure-mesomorphic property relationship for new functional reactive mesogens, aiming at further design of smart self-assembling macromolecular materials for novel sensor systems.

Deuteron NMR investigation on orientational order parameter in polymer dispersed liquid crystal elastomers

Polymer-dispersed liquid crystal elastomers have been recently introduced as a thermomechanically active composite material, consisting of magnetically oriented liquid crystal elastomer particles incorporated in a cured polymer matrix. Their thermomechanical properties are largely governed by the degree of imprinted particle alignment, which can be assessed by means of deuterium perturbed 2H-NMR. Spectra of samples with various degrees of imprinted particle alignment were recorded and the results simulated using the discrete reorientational exchange model developed for determining the dispersion of liquid crystal elastomer's domain orientational distribution. We show that the model can be applied to measure the orientational distribution of embedded liquid crystal microparticles and successfully determine the orientational order parameter in the composite system. Thermomechanical measurements correlate well with the obtained results, thus additionally confirming the validity of the applied method.

Nanostructured Composites Based on Liquid-Crystalline Elastomers

Liquid-crystalline elastomers (LCEs) are the object of many research investigations due to their reversible and controllable shape deformations, and their high potential for use in the field of soft robots and artificial muscles. This review focuses on recent studies about polymer composites based on LCEs and nanomaterials having different chemistry and morphology, with the aim of instilling new physical properties into LCEs. The synthesis, physico-chemical characterization, actuation properties, and applications of LCE-based composites reported in the literature are reviewed. Several cases are discussed: (1) the addition of various carbon nanomaterials to LCEs, from carbon black to carbon nanotubes, to the recent attempts to include graphene layers to enhance the thermo-mechanic properties of LCEs; (2) the use of various types of nanoparticles, such as ferroelectric ceramics, gold nanoparticles, conductive molybdenum-oxide nanowires, and magnetic iron-oxide nanoparticles, to induce electro-actuation, magnetic-actuation, or photo-actuation into the LCE-based composites; (3) the deposition on LCE surfaces of thin layers of conductive materials (i.e., conductive polymers and gold nanolayers) to produce bending actuation by applying on/off voltage cycles or surface-wrinkling phenomena in view of tunable optical applications. Some future perspectives of this field of soft materials conclude the review.

Deuteron NMR resolved mesogen vs. crosslinker molecular order and reorientational exchange in liquid single crystal elastomers

²H NMR spectroscopy can resolve differences in orientational order and reorientational dynamics between crosslinker and mesogen molecules in liquid single crystal elastomers.