Imine-Based Reactive Mesogen and Its Corresponding Exchangeable Liquid Crystal Elastomer

Controlled Mesoscopic Growth of Polymeric Fibers Using Liquid Crystal Template

Orientation-controlled polymeric fiber is one of the most exciting research topics to rationalize the multifunctionality for various applications. In order to realize this goal, the growth of polymeric fibers should be controlled using various techniques like extrusion, molding, drawing, and self-assembly. Among the various candidates to fabricate the orientation-controlled polymeric fibers, the template-assisted assembly guided by a liquid crystal (LC) matrix is the most promising because the template can be manipulated easily with various methods like surface anchoring, rubbing, geometric confinement, and electric field. This review introduces the recent progress toward the directed growth of polymeric fibers using the LC template. Three representative LC-templated polymerization techniques to fabricate fibers include chemical or physical polymerization from the monomers mixed in LC matrix, patterned fibers formed from LC-templated reactive mesogens, and orientation-controlled nanofibers by infiltrating vaporized monomers between LC molecules. The orientation-controlled polymeric fibers will be used in electro-optical switching tools, tunable hydrophilic or hydrophobic surfaces, and control of phosphorescence, which can open a way to design, fabricate, and modulate nano- to micron-scale fibers with various functions on demand.

Liquid Crystal Elastomers: 30 Years After

This is a Review that attempts to cast a look at the whole history of liquid crystal elastomers and the evolution of this field from its inception to the current state of the art. The exposition is limited by deliberately omitting several important elements of this field, such as densely cross-linked networks or smectic elastomers, focusing solely on the nematic phase of these elastomers. In this more narrow topic, we first discuss the current developments and perspectives in the materials chemistry. This is followed by three sections, each dedicated to one of the three main points of interest in the nematic liquid crystal elastomers: the reversible actuation, the soft elasticity, and the viscoelastic dynamics of nematic elastomers. In each of these directions, there have been significant developments over recent years but equally significant new avenues emerging for the research to follow.

Thermal Actuators Relying on Elastomer-Dispersed Liquid Crystals: From Imines with Supramolecular Chirality and Ferroelectricity to Soft Robots

The locomotion of various organisms relies on the alternated elongation-contraction of their muscles or bodies. Such biomimicry can offer a promising approach to developing soft robotic devices with improved mobility and efficiency. Most strategies to mimic such motions rely on reversible size modifications of some materials upon exposure to external stimuli. An example is the combination of liquid crystals (LCs) with elastomers that afford materials with reversible and programmable shape morphing upon heat treatment. This strategy is supposed to involve mainly liquid crystalline elastomers or liquid crystalline networks, but low molecular weight LCs were disregarded. Unlike the previous routes, we utilized a new type of thermal actuator, i.e., elastomer-dispersed LCs (EDLCs), where the LCs rely on small organic molecules, i.e., salicylaldimines with 1,3,4-thiadiazole core and silane or siloxane as mobility units. The individual components of EDLC are not chemically bound and have the advantage of retaining their intrinsic properties. By combining their particularities, herein we highlighted: rare molecules with supramolecular chirality and piezo-/ferroelectricity, new thermal actuators with >340% strain actuation, programmable twisting actuation through helical patterning of elastomers with cholesteric LCs, and crawler and walker soft robots, which show bidirectional gait with high speeds up to 2 mm s-1.

Cluster-Triggered Self-Luminescence, Rapid Self-Healing, and Adaptive Reprogramming Liquid Crystal Elastomers Enabled by Dynamic Imine Bond

The integration of advanced functions and diverse practical applications calls for multifunctional liquid crystal elastomers (LCEs); however, the structure-intrinsic luminescence and excellent mechanical properties of LCEs have not yet been explored. In this study, clusteroluminescence (CL)-based LCEs (CL-LCEs) are successfully fabricated without depending on large conjugated structures, thereby avoiding redundant organic synthesis and aggregation-caused quenching. The experimental and theoretical results reveal that secondary amine (-NH-) and imine (-C = N-) groups play vital roles in determining the presence of fluorescence in CL-LCEs. Based on the above observation, the strategy universalization and a molecular library for constructing CL-LCEs are further demonstrated. Meanwhile, the dynamic bond of imine bonds endows the CL-LCE system with rapid self-healing under mild conditions (70 °C in 10 min), excellent stretchability, and adaptive programmable characteristics. Furthermore, the self-luminescent performance enables visual detection of the self-healing process. Finally, CL-based information storage and anticounterfeiting are successfully realized and their applications in fiber actuators and fluorescent textiles are demonstrated. The distinctive luminescence and dynamic chemistry presented in this work has significant implications in elucidating the mechanism of CL and providing new strategies for the rational design of novel multifunctional LCE materials.

Photoinduced Phase Transitions of Imine-Based Liquid Crystal Dimers with Twist-Bend Nematic Phases

Photoisomerizable molecules in liquid crystals (LCs) allow for photoinduced phase transitions, facilitating applications in a wide variety of photoresponsive materials. In contrast to the widely investigated azobenzene structure, research on the photoinduced phase-transition behavior of imine-based LCs is considerably limited. We herein report the thermal and photoinduced phase-transition behaviors of photoisomerizable imine-based LC dimers with twist-bend nematic (NTB) phases. We synthesize two homologous series of ester- and thioether-linked N-(4-cyanobenzylidene)aniline-based bent-shaped LC dimers with an even number of carbon atoms (n = 2, 4, 6, 8, and 10) in the central alkylene spacers, namely, CBCOOnSBA(CN) and CBOCOnSBA(CN), possessing oppositely directed ester linkages, C=OO and OC=O, respectively. Their thermal phase-transition behavior is examined using polarizing optical microscopy and differential scanning calorimetry. All dimers form a monotropic NTB phase below the temperature of the conventional nematic (N) phase upon cooling. Remarkably, the NTB phases of CBCOOnSBA(CN) (n = 2, 4, 6, and 8) and CBOCOnSBA(CN) (n = 6 and 8) supercool to room temperature and vitrify without crystallization. In addition, the phase-transition temperatures and entropy changes of CBCOOnSBA(CN) are lower than those of CBOCOnSBA(CN) at the same n. Under UV light irradiation, the NTB and N phases transition to the N and isotropic phases, respectively, and reversibly return to their initial LC phases when the UV light is turned off.

Isothermal Phase Transitions in Liquid Crystals Driven by Dynamic Covalent Chemistry

The dynamic nature of calamitic liquid crystals is exploited to perform isothermal phase transitions driven by dynamic covalent chemistry. For this purpose, nematic (N) arrays based on aldehyde 1 were treated with different amines (A-E) in an on-surface process, which resulted in different isothermal phase transitions. These phase transformations were caused by in situ imination reactions and are dependent on the nature of the added amine. Transitions from the N to crystal (1A, 1E), isotropic (1B), and smectic (Sm) (1C, 1D) phases were achieved, while the resulting materials feature thermotropic liquid crystal behavior. A sequential transformation from the N 1 to the Sm 1C and then to the N 1B was achieved by coupling an imination to a transimination processes and adjusting the temperature. All of these processes were well characterized by microscopic, spectroscopic, and X-ray techniques, unlocking not only the constitutional but also the structural aspects of the phase transitions. This work provides new insights into designing constitutionally and structurally adaptable liquid crystal systems, paving the way toward the conception of programable evolutive pathways and adaptive materials.

Effect of methyl methacrylate concentrations on surface and thermal analysis of composite polymer polymethylmethacrylates with mesogen reactive RM82

This research report of the synthesis of composite polymers from liquid crystal mesogen reactive (RM82) monomers with Methyl methacrylate (MMA). The purpose of this research is analysis the effect concentration of MMA on the surface and thermal of the composite polymer PMMA-RM82. The result of the morphological analysis of composite surfaces performed by polarization optical microscopy (POM) technique showed liquid crystal textures affected composition from two monomers. SEM images show that the surface of the RM82 liquid crystal has a shape resembling fibrous and blade-like crystals with a length of up to 10 μm (micrometers). Analysis thermal showed the heat released by the PMMA-RM82 increased with the increase in MMA weight percent. This affects the rapid crystallization process of PMMA-RM82 which of concentration MMA 30%-RM82 the heat released is almost twice as much as the heat released by MMA 5%-RM82. The absence of PMMA and RM82 peaks both endothermic and exothermic in PMMA-RM82 samples indicates that polymerization has occurred and a new product has formed. Analysis structure molecule by FTIR found that the IR spectral form of each variation in the weight percent of MMA was almost the same, but there was a spectral shift that showed that polymerization had occurred in PMMA-RM82 which was characterized by a reaction to the free radical C=C bond released by the photoinitiator. XRD pattern of composite PMMA-RM82 showed the peaks formed are located at scattering angles similar to RM82 but there is a decrease in intensity as the percent weight of MMA increases.

Manipulation of Liquid Crystalline Properties by Dynamic Covalent Chemistry─En Route to Adaptive Materials

Dynamic covalent bonds bear great potential for the development of adaptive and self-healing materials. Herein, we introduce a versatile concept not only for the design of low-molecular-weight liquid crystals but also for their in situ postsynthetic modification by using the dynamic covalent nature of imine bonds. The methodology allows systematic investigations of structure-property relationships as well as the manipulation of the materials' behavior (liquid crystallinity) and the introduction of additional properties (here, fluorescence) by a solvent-free method. For the first time, the transamination reaction is followed by variable-temperature ¹⁹F solid-state NMR in the mesophase, providing insights into the reaction dynamics in a liquid crystalline material. Finally, the application potential for the design of liquid crystalline materials with adaptive properties is demonstrated by a sequential combination of these reactions.