The monodomain nematic liquid crystal elastomer (LCE) is a nonporous material with one-dimension (1D) negative thermal expansion (NTE) along the direction of orientation. This stimuli-responsive size change is comparable with the contractile response of a muscle fibre. Recently, LCEs have become more and more popular and increasingly investigated as a full-fledged class of stimuli-responsive materials. However, the nematic LCE is limited to a single, unidirectional deformation unless complex hybrid architectures are made. We develop here a special LCE based on a liquid crystal polymer with an extraordinary phase transition sequence, “re-entrant nematic (NRe) – smectic A (SmA) – nematic (N) – isotropic (I) phase”, along with “prolate – oblate – weakly oblate – spherical” chain conformation evolution. In the aligned LCE film, these conformational changes of polymer chain are observed with the naked eye through their macroscopic translations into a unique sequence of “contraction – expansion – second expansion” deformations. Notably, a switch from NTE to positive thermal expansion (PTE) occurs upon heating. Moreover, a bilayer actuator composed of aligned and non-aligned LCE layers can perform 2D to 3D shape transformation with “curling – uncurling – second uncurling” actuation sequence. This LCE capable of multiple deformations in response to a single stimulus paves the way to multimodal single-material actuators. It provides a new strategy for the development of advanced materials with adjustable and multidirectional deformations.

Stimuli-responsive patterned photonic actuators, characterized by their patterned nano/microscale structures and capacity to demonstrate synergistic color changes and shape morphing in response to external stimuli, have attracted intense scientific attention. However, traditional patterned photonic actuator systems still face limitations such as cumbersome and time-consuming preparation processes and small-scale deformations. Herein, we introduce a facile approach involving an athermal embossing technique to rapidly fabricate patterned photonic actuators based on near-infrared (NIR) light-responsive liquid crystal elastomers. The resulting patterned photonic actuators demonstrate remarkable features, including brilliant angle-dependent structural color, complex three-dimensional actuation, and good color durability under NIR light stimulation. As illustrative demonstrations of the proof-of-concept, we fabricate two light-fuelled patterned photonic soft actuators: a butterfly-inspired actuator that can produce wing-flapping dynamic changes in structural color, and an origami crane-shaped actuator with shape memory, structural color information storage, and dynamic display properties. This strategy provides distinct insights into the design and fabrication of various patterned photonic soft robotic devices and intelligent actuators.

Control of physical behaviors of nematic colloids and colloidal crystals has been demonstrated by tuning particle shape, topology, chirality and surface charging. However, the capability of altering physical behaviors of such soft matter systems by changing particle shape and the ensuing responses to external stimuli has remained elusive. We fabricated genus-one nematic elastomeric colloidal ring-shaped particles and various microstructures using two-photon photopolymerization. Nematic ordering within both the nano-printed particle and the surrounding medium leads to anisotropic responses and actuation when heated. With the thermal control, elastomeric microstructures are capable of changing from genus-one to genus-zero surface topology. Using these particles as building blocks, we investigated elastomeric colloidal crystals immersed within a liquid crystal fluid, which exhibit crystallographic symmetry transformations. Our findings may lead to colloidal crystals responsive to a large variety of external stimuli, including electric fields and light. Pre-designed response of elastomeric nematic colloids, including changes of colloidal surface topology and lattice symmetry, are of interest for both fundamental research and applications.

Stimuli-responsive liquid crystal elastomers (LCEs), which exhibit sophisticated and versatile shape variations and functions upon stimulations, have constantly interested material science researchers. To date, many challenges still exist in scaling up orientated LCEs with sophisticated physical shapes and multi-functions. Herein, LCEs with various customizable conventional and exotic three-dimensional (3D) shapes and with sizes larger than those previously reported have been prepared by combining magnetic field alignment and soft lithography technology. These LCEs have film, cylinder, ellipsoid, hemispheroid, tube, pyramid, triangle and rectangle frame, grid pattern, cubic frame, and spring shapes. Meanwhile, diversified deformation behaviors such as contraction, expansion, bending, and twisting have been achieved by effectively controlling the alignment directions. Finally, the LCE actuator with hemispheroid shape has been explored for its possible applications in dynamic Braille displays or lenses with adjustable focal length. The simple strategy reported here provides a convenient way to customize multimorphological large-size 3D LCE actuators and their stimuli-responsive deformations. These systems will considerably enlarge the potential applications of LCEs and benefit the development of LCE soft robots and the future special bionic systems.

Nature provides well‐engineered and evolutionary optimized examples of brilliant structural colors in animals and plants. Morpho butterflies are among the well‐known species possessing iridescent bright blue coloration due to multiple optical effects generated by the complex structuration of the wing scales. Such surprising solution can be replicated to fabricate efficient devices. Maybe even more interesting, novel approaches can be developed to combine wings with synthetic smart materials to achieve complex structures responsive to external stimuli. This study demonstrates the proof of concept of an innovative biotic–abiotic hybrid smart structure made by the integration of a butterfly wing with thermoresponsive liquid crystalline elastomers, and their capability to actuate the mechanical action of the wing, thus controlling its spectral response. Exploiting two fabrication strategies, it is demonstrated how different mechanisms of color tuning can be achieved by temperature control. In addition, due to the thermally induced mechanical deformation of the elastomer and superhydrophobic properties of the wing, a potential self‐cleaning behavior of the bilayer material is demonstrated.

The research on soft actuators including liquid crystal elastomers (LCEs) becomes more and more appealing at a time when the expansion of artificial systems is blooming. Among the various LCE actuators, the bending deformation is often in the origin of many actuation modes. Here, a new strategy with plasma technology is developed to prepare single-layer main-chain LCEs with thermally actuated bending and contraction deformations. Two distinct reactions, plasma polymerization and plasma-induced photopolymerization, are used to polymerize in one step the nematic monomer mixture aligned by magnetic field. The plasma polymerization forms cross-linked but disoriented structures at the surface of the LCE film, while the plasma-induced photopolymerization produces aligned LCE structure in the bulk. The actuation behaviors (bending and/or contraction) of LCE films can be adjusted by plasma power, reaction time, and sample thickness. Soft robots like crawling walker and flower mimic are built by LCE films with bending actuation.

Liquid crystal elastomer micropillars containing β-cyano-OPV crosslinkers contract reversibly at nematic–isotropic (N–I) phase transition and undergo fluorescence intensity change. This luminescent variation is mainly caused by N–I phase change.

In this communication, we describe a two-stage temperature-varied photopatterning protocol to synthesize a series of single-layer dual-phase liquid crystalline elastomer films, which have the capabilities to perform versatile three-dimensional motions, such as bending, accordion-folding, wrinkling, curling, and buckling, under thermal stimulus.

In the present study, the optical, thermal, and mechanical properties of liquid crystal elastomers (LCEs) were investigated using various techniques. The presence of functional groups in LCE was studied using Fourier transform infrared spectroscopy. The phase transition temperatures were confirmed via polarizing optical microscopy and Fabry–Perot scattering studies. The differential thermal analysis was used for investigating the thermal behavior. A dynamic mechanical analysis was used to study the mechanical properties of LCE. The significant mechanical changes with a considerable reversible effect were observed for this soft material. The changes in the mechanical shape with the temperature are attributed to the change in the phase of the LCE material.

School of Chemistry and Chemical Eng Laboratory for Bio-medical Research, Jian and Engineering Laboratory, Southeast Uni yangh@seu.edu.cn; Tel: +86-25-52090620 Institut Curie, PSL Research University, CN Sorbonne Universités, UPMC Univ Paris 06 So Materials Research Center and Depa University of Colorado, Boulder, CO 80309, † Electronic supplementary informatio descriptions, synthetic protocols, NMR (S1.avi). See DOI: 10.1039/c6sc00758a Cite this: Chem. Sci., 2016, 7, 4400

Homeotropically-aligned main-chain and side-on liquid crystalline elastomer films are prepared by using LC thiol-ene and acrylate systems respectively. Evaluated by laser flash analysis, the room temperature thermal conductivities of these two LCP films in the film normal direction are both dramatically higher than those along the horizontal direction.

Liquid crystal elastomers (LCEs) capable of rapid reversible shape change and ease of actuation at room temperature are highly desired. In this study, a photothermally actuated system based on LCE gel micropillars incorporated with gold nano particles is reported for the first time. The photothermal conversion effects of gold nanoparticles (AuNPs) have been studied with a focus on nanoparticle shape (rods and spheres) and loading content. Upon swelling in low molecular mass liquid crystal solvent, the formation of LCE and LCE/AuNP gel enables the reduction of nematic-to-isotropic phase transition temperature (T-NI), which allows the gelled micropillar capable of photothermal actuation at room temperature. It has been demonstrated that the LCE gel micropillar with incorporation of 1.0 wt % of gold nanorods can achieve a rapid 30% change in volume within 3 s when under proper laser irradiation at room temperature. The observed discontinuous volumetric transition of the gel micropillars is in good agreement with the mean field theory prediction. A simple finite element analysis (FEA) model was developed to facilitate the understanding of the photothermal effect of LCE/AuNR gel micropillar upon laser irradiation.

Using adaptive soft materials to fabricate microstructured surfaces renders them with tunable topographic feature and thus controllable physical properties. Here, light responsive microstructured surfaces are reported with shape memory and tunable wetting behaviors; the surfaces are covered with micropillar arrays and constructed by lightly crosslinked azo-containing liquid crystalline network (LCN). UV light irradiation induces 25% contraction in length of the micropillars along their long axes and, as a consequence, the variations of topographic feature and wetting behavior of the surfaces. In addition, the LCNs exhibit shape memory properties, which can freeze the temporary topographic feature of microstructured surfaces (formed under UV irradiation and relatively high temperature) and enable application of their functionalities at mild conditions. This light responsiveness makes it feasible to remotely and precisely tune the local regions of microstructured surfaces, which should broaden the applications of adaptive surfaces in regulating the wetting, optical, and adhesion properties in selected regions.

In this work, we report the first example of a calamitic mesogenic near-infrared (NIR) absorbing organic dye, made by functionalizing a thiophene-croconaine chromophore rigid core with two symmetric long flexible alkyl chains. The liquid crystal (LC) NIR dye YHD796 exhibits a sharp and intense NIR absorption band with a maximum absorption peak at 796 nm. Taking advantage of the improved solubility of YHD796 dispersed in mesogenic molecules, a homogeneously-aligned mono-domain liquid crystalline elastomer (LCE)/YHD796 composite film is successfully prepared by applying the classical LC-cell-alignment method and in situ photo-polymerization of photocurable LC monomer mixtures. This LCE/YHD796 composite film performs a fully reversible contraction/expansion response towards NIR light stimulus due to the photothermal heating effect induced by the YHD796 dye well-dispersed in the LCE matrix.

It is highly desirable for liquid crystal elastomer (LCE) based microactuators to activate and actuate in a highly controlled fashion without perturbing the surrounding environment. To reach this goal, in this study, a novel experimental protocol is developed to successfully incorporate gold nanosphere (AuNS) and gold nanorod (AuNR) into polyacrylate based LCE elastomer to fabricate LCE/AuNR and LCE/AuNS micropillars or microactuators. The effect of gold nanoparticle inclusion has been studied by spectroscopy (UV–vis‐near‐infrared), microscopy (transmission electron microscopy), thermal analysis (differential scanning calorimetry and thermogravimetric analysis), and x‐ray scattering (wide‐angle x‐ray scattering and small‐angle x‐ray scattering). Finite element analysis is performed to examine the feasibility of utilizing the photothermal effect of AuNR/AuNS to enable photothermal actuation of LCE/AuNR and LCE/AuNS micropillars. The comparative experimental studies on the thermal and photothermal actuation behavior of the LCE, LCE/AuNS, and LCE/AuNR micropillar suggested that AuNR is an excellent candidate for developing high‐performance LCE actuators with photothermal actuation capability. With inclusion of less than 1 wt% of AuNR, the very high maximum actuation strain (30%) and rapid response (a few seconds) have been achieved in LCE/AuNR micropillar actuators under 635 nm laser irradiation.

The structure and influence of temperature on mechanical deformation of Liquid Crystal Elastomers (LCEs) were studied using various techniques like Raman Spectroscopy (RS), Fourier Transform Infrared (FTIR) Spectroscopy and Polarizing Microscopy Studies (PMS) etc. The spectroscopic studies confirmed the presence of functional group attached to the sample. The shrinkage in length was observed while heating whereas material returns to its original length on cooling which revealed the correlation of mechanical behavior of Liquid Crystal Elastomers with temperature. This spontaneous shape changing property indicates that LCE material plays an important role in biological applications.

Most of the traditional chiral side-chain liquid crystalline polymers (SCLCPs) depend on pendant chiral mesogenic units to introduce chirality into their structure, with the polymer backbones being usually achiral. In this work, we asymmetrically synthesize several enantiomerically pure norbornene monomers functionalized with achiral mesogenic units, and further apply a ring-opening metathesis polymerization technique to prepare a series of side-on and end-on SCLCPs with an optically active polynorbornene main chain and achiral mesogens. Their physical properties are fully characterized by NMR, UV, CD, GPC, TGA, DSC, polarimetry, polarized optical microscopy and small-angle X-ray scattering. The obtained sideon SCLCPs display the tendency to form nematic, i.e. achiral mesophases, in strong contrast to the chiral nematic (cholesteric) mesophase exhibited by their comparative end-on analogues. The proposed explanation for this phenomenon is that the chiral backbones and the laterally attached mesogens of side-on SCLCPs can concurrently exist in a parallel arrangement so that the mesogenic directors might not be affected by the chirality information, while the mesogenic directors of end-on SCLCPs always tilt to the backbone orientation so that the twisting power of chiral main chains might force the terminally attached mesogens to form helical structures.

A novel NIR-responsive GNR/LCE composite fiber material was prepared by a three-step sequential thiol-click chemistry approach. Taking advantage of GNRs' significant photo-thermal effect, a GNR/LCE composite material with a very low Au loading-level (0.09 wt%), under 808 nm NIR stimulus achieved the N-to-I transition and shrank dramatically in an ambient environment.

Nematic liquid crystalline elastomer (LCE) microactuators are developed, showing simultaneous thermomechanical deformation and photoluminescence (PL) emission variation functions. The microactuators are prepared by a method combining soft-lithography and photo-polymerization/crosslinking. 1,4-Bis(α-cyano-4-methoxystyryl)benzene as the PL dye is synthesized, characterized, and introduced into LCEs as a dopant in the preparation process. During the heating process, PL emission of the LCE micropillars under blue light excitation becomes significantly weak when the micropillars contract. When cooling down, the emission completely recovers as the micropillars stretches back to their original shape. The PL intensity variation at the transition is proved to be related to the thermomechanical deformation.

Nematic liquid crystalline elastomer (LCE) actuators possessing both photoluminescent (PL) and stimuli-responsive functions were fabricated and studied. PL-dyes (1-pyrenemethyl acrylate and 4-bromo-2,6-bis-(1MODIFIER LETTER PRIME-methyl-benzimidazolyl) pyridine loaded with Eu(III) ion) were synthesised and characterised, and then the dyes were mixed with an acrylate side-on liquid crystalline monomer, a cross-linker and a photo-initiator. Through magnetic field alignment, well-defined LCE micropillar PL actuators were fabricated from the mixed samples by a method combining soft lithography and photo-polymerisation/photo-cross-linking. Microscopic observations indicated that the LCE micropillars showed reversible thermomechanical deformation at the nematic-to-isotropic transition temperature. During the reversible contraction and extension process, the LCE actuator containing 1-pyrenemethyl moieties showed stable photoluminescence, while for the LCE actuator doped with 4-bromo-2,6-bis-(1-methyl-benzimidazolyl)pyridine/Eu(III) complex, the PL emission was quenched at about 100 degrees C, which was before the pillars contraction occurring at a higher temperature. When cooled down to room temperature, the contracted LCE micropillars recovered their original shape and the initial PL emission state. The micron-sized LCE actuators can be used for thermomechanical devices and machines with different PL functions at the same time.