Topography from topology: photoinduced surface features generated in liquid crystal polymer networks

Liquid crystal polymer actuators with complex and multiple actuations

Deformable liquid crystal polymers (LCPs), which exhibit both entropic elasticity of polymer networks and anisotropic properties originating from ordered mesogens, have gained more and more interest for use as biomedical soft actuators. Especially, LCP actuators with controllable mesogen alignment, sophisticated geometry and reprogrammability are a rising star on the horizon of soft actuators, since they enable complex and multiple actuations. This review focuses on two topics: (1) the regulation of mesogen alignment and geometry of LCP actuators for complex actuations; (2) newly designed reprogrammable LCP materials for multiple actuations. First, basic actuation mechanisms are briefly introduced. Then, LCP actuators with complex actuations are demonstrated. Special attention is devoted to the improvement of fabrication methods, which profoundly influence the available complexity of the mesogen alignment and geometry. Subsequently, reprogrammable LCP actuators featuring dynamic networks or shape memory effects are discussed, with an emphasis on their multiple actuations. Finally, perspectives on the current challenges and potential development trends toward more intelligent LCP actuators are discussed, which may shed light on future investigations in this field.

Responsive Liquid Crystal Network Microstructures with Customized Shapes and Predetermined Morphing for Adaptive Soft Micro-Optics

Stimuli-responsive materials have garnered substantial interest in recent years, particularly liquid crystal networks (LCNs) with sophisticatedly designed structures and morphing capabilities. Extensive efforts have been devoted to LCN structural designs spanning from two-dimensional (2D) to three-dimensional (3D) configurations and their intricate morphing behaviors through designed alignment. However, achieving microscale structures and large-area preparation necessitates the development of novel techniques capable of facilely fabricating LCN microstructures with precise control over both overall shape and alignment, enabling a 3D-to-3D shape change. Herein, a simple and cost-effective in-cell soft lithography (ICSL) technique is proposed to create LCN microstructures with customized shapes and predesigned morphing. The ICSL technique involves two sequential steps: fabricating the desired microstructure as the template by using the photopolymerization-induced phase separation (PIPS) method and reproducing the LCN microstructures through templating. Meanwhile, surface anchoring is employed to design and achieve molecular alignment, accommodating different deformation modes. With the proposed ICSL technique, cylindrical and spherical microlens arrays (CMLAs and SMLAs) have been successfully fabricated with stimulus-driven polarization-dependent focusing effects. This technique offers distinct advantages including high customizability, large-area production, and cost-effectiveness, which pave a new avenue for extensive applications in different fields, exemplified by adaptive soft micro-optics and photonics.

Melt electrowriting enabled 3D liquid crystal elastomer structures for cross-scale actuators and temperature field sensors

Liquid crystal elastomers (LCEs) have garnered attention for their remarkable reversible strains under various stimuli. Early studies on LCEs mainly focused on basic dimensional changes in macrostructures or quasi-three-dimensional (3D) microstructures. However, fabricating complex 3D microstructures and cross-scale LCE-based structures has remained challenging. In this study, we report a compatible method named melt electrowriting (MEW) to fabricate LCE-based microfiber actuators and various 3D actuators on the micrometer to centimeter scales. By controlling printing parameters, these actuators were fabricated with high resolutions (4.5 to 60 μm), actuation strains (10 to 55%), and a maximum work density of 160 J/kg. In addition, through the integration of a deep learning-based model, we demonstrated the application of LCE materials in temperature field sensing. Large-scale, real-time, LCE grid-based spatial temperature field sensors have been designed, exhibiting a low response time of less than 42 ms and a high precision of 94.79%.

Dynamic Shape Change of Liquid Crystal Polymer Based on An Order-Order Phase Transition

Liquid crystal actuators conventionally undergo shape changes across an order-disorder phase transition between liquid crystal (LC) and isotropic phases. In this study, we introduce an innovative Liquid Crystal Polymer (LCP) actuator harnessing an order-order LC phase transition mechanism. The LCP film is easily stretchable within the LC phase, facilitated by the π-π stacking of phenyl groups serving as robust physical crosslinking points, and thereby transforms to a stable monodomain structure. The resultant monodomain LCP actuator shows a distinctive reversible dynamic shape change, exhibiting extension followed by contraction along the LC director on cooling. The extension is propelled by the reversible smectic C to smectic A phase transition, and the contraction is attributed to the re-entry to the smectic C phase from smectic A phase. Thermal annealing temperature determines this peculiar dynamic shape change, which occurs during both heating and cooling processes. This pivotal attribute finds manifestation in gripper and flower-shaped actuators, adeptly executing grabbing and releasing as well as blooming and closure motions within a single thermal stimulation. In essence, our study introduces an innovative approach to the realm of LCP actuators, ushering in a new avenue for the design and fabrication of versatile and dynamically responsive LCP actuators.

Unrestricted Chiral Patterning by Laser Writing in Liquid Crystalline and Plasmonic Nanocomposite Thin Films

Obtaining hierarchical structures with arbitrarily controlled chirality remains a challenge. Here, thin films featuring chiroptically bipolar patterns are produced by a device utilizing microscale photothermal re-melting of materials exhibiting chirality synchronization. This device operates autonomously, guided by an algorithm that facilitates the homochiral growth of supramolecular organic helices through controlling their re-melting. The chirality synchronization phenomena of constitutionally achiral molecules grants availability of both handednesses of the helices, enabling unrestricted chiral writing in the film. The collective chiroptical response of assembled molecules is utilised to guide the patterning process, creating a foundation for optically secured information. The established methodology enables achieving dissymmetry factor values for circular dichroism (CD) a magnitude higher than previously reported, as confirmed with state-of-the-art, synchrotron-based Mueller matrix polarimetry (MMP). Moreover, the developed method is extended to nanocomposites comprising gold nanoparticles, providing the opportunity to tune the CD toward the plasmonic region. This strategic application of photothermal processing, specifically laser-directed melting, uncovers the potential to broaden the selection of nanostructured materials with precisely designed functionalities for photonic applications.

Recent Trends in Continuum Modeling of Liquid Crystal Networks: A Mini-Review

This work aims to provide a comprehensive review of the continuum models of the phase behaviors of liquid crystal networks (LCNs), novel materials with various engineering applications thanks to their unique composition of polymer and liquid crystal. Two distinct behaviors are primarily considered: soft elasticity and spontaneous deformation found in the material. First, we revisit these characteristic phase behaviors, followed by an introduction of various constitutive models with diverse techniques and fidelities in describing the phase behaviors. We also present finite element models that predict these behaviors, emphasizing the importance of such models in predicting the material's behavior. By disseminating various models essential to understanding the underlying physics of the behavior, we hope to help researchers and engineers harness the material's full potential. Finally, we discuss future research directions necessary to advance our understanding of LCNs further and enable more sophisticated and precise control of their properties. Overall, this review provides a comprehensive understanding of the state-of-the-art techniques and models used to analyze the behavior of LCNs and their potential for various engineering applications.

Continuous Flow Microfluidic Production of Arbitrarily Long Tubular Liquid Crystal Elastomer Peristaltic Pump Actuators

While liquid crystal elastomers (LCEs) are ideal materials for soft-robotic actuators, filling the role of muscle and shape-defining material simultaneously, it is non-trivial to give them ground state shapes beyond simple sheets or fibers. Here tubular LCE actuators scalable to arbitrary length are produced using a continuous three-phase coaxial flow microfluidic process. By pumping an oligomeric precursor solution between inner and outer aqueous phases in a cylindrically symmetric nested capillary set-up, and by reducing the interfacial tension to negligible values using surfactants adapted to each phase, the tubular liquid flow is stabilized over distances more than 200 times the diameter or 2000 times the thickness. In situ photocrosslinking of the middle phase turns it into an LCE network that is flow-aligned by the shear gradient over the phase. The reversible actuation of the tubes upon heating yields a reduction of the interior space, pumping out enclosed fluid, and the relaxation upon cooling leads to the fluid being sucked back in. By moving a local heat source along the tube, it acts as a peristaltic pump. It is proposed that the tubes could, pending functionalization for light-triggered actuation, function as active synthetic vasculature in biological contexts.

Degree of Orientation in Liquid Crystalline Elastomers Defines the Magnitude and Rate of Actuation

The anisotropy of liquid crystalline elastomers (LCEs) is derived from the interaction-facilitated orientation of the molecular constituents. Here, we correlate the thermomechanical response of a series of LCEs subjected to mechanical alignment to measurements of the Hermans orientation parameter. The LCEs were systematically prepared with varying concentrations of liquid crystalline mesogens, which affects the relative degree of achievable order. These compositions were subject to varying degrees of mechanical alignment to prepare LCEs with orientations that span a wide range of orientation parameters. The stimuli-response of the LCEs indicates that the liquid crystalline content defines the temperature of actuation, whereas the orientation parameter of the LCE is intricately correlated to both the total actuation strain of the LCE as well as the rate of thermomechanical response.

Shape Morphing by Topological Patterns and Profiles in Laser-Cut Liquid Crystal Elastomer Kirigami

Programming shape changes in soft materials requires precise control of the directionality and magnitude of their mechanical response. Among ordered soft materials, liquid crystal elastomers (LCEs) exhibit remarkable and programmable shape shifting when their molecular order changes. In this work, we synthesized, remotely programmed, and modeled reversible and complex morphing in monolithic LCE kirigami encoded with predesigned topological patterns in its microstructure. We obtained a rich variety of out-of-plane shape transformations, including auxetic structures and undulating morphologies, by combining different topological microstructures and kirigami geometries. The spatiotemporal shape-shifting behaviors are well recapitulated by elastodynamics simulations, revealing that the complex shape changes arise from integrating the custom-cut geometry with local director profiles defined by topological defects inscribed in the material. Different functionalities, such as a bioinspired fluttering butterfly, a flower bud, dual-rotation light mills, and dual-mode locomotion, are further realized. Our proposed LCE kirigami with topological patterns opens opportunities for the future development of multifunctional devices for soft robotics, flexible electronics, and biomedicine.

Automated photo-aligned liquid crystal elastomer film fabrication with a low-tech, home-built robotic workstation

Laboratory procedures are often considered so unique that automating them is not economically justified - time and resources invested in designing, building and calibrating the machines are unlikely to pay off. This is particularly true if cheap labour force (technicians or students) is available. Yet, with increasing availability and dropping prices of many off-the-shelf components such as motorised stages, grippers, light sources (LEDs and lasers), detectors (high resolution, fast cameras), as well as user-friendly programmable microprocessors, many of the repeatable tasks may soon be within reach of either custom-built or universal lab robots. Building on our previous work on fabrication, characterization and applications of light-responsive liquid crystal elastomers (LCEs) in micro-robotics and micro-mechanics, in this paper we present a robotic workstation that can make LCE films with arbitrary molecular orientation. Based on a commercial 3D printer, the RoboLEC (Robot for LCE fabrication) performs precision component handling, structured light illumination, liquid dispensing and UV-triggered polymerization, within a four-hour-long procedure. Thus fabricated films with patterned molecular orientation are compared to the same, but handmade, structures.

Controlled gel expansion through colloid oscillation

We model the behavior of a single colloid embedded in a cross-linked polymer gel, immersed in a viscous background fluid. External fields actuate the particle into a periodic motion, which deforms the embedding matrix and creates a local microcavity, containing the particle and any free volume created by its motion. This cavity exists only as long as the particle is actuated and, when present, reduces the local density of the material, leading to swelling. We show that the model exhibits rich resonance features, but is overall characterized by clear scaling laws at low and high driving frequencies, and a pronounced resonance at intermediate frequencies. Our model predictions suggest that both the magnitude and position of the resonance can be varied by varying the material's elastic modulus or cross-linking density, whereas the local viscosity primarily has a dampening effect. Our work implies appreciable free-volume generation is possible by dispersing a collection of colloids in the medium, even at the level of a simple superposition approximation.

Photothermal Thin Films with Highly Efficient NIR Conversion for Miniaturized Liquid-Crystal Elastomer Actuators

This work presents the development of highly efficient photothermal thin films (PTFs) and the demonstration of their application on miniaturized polymer-based soft actuators. The proposed PTF, which comprises acrylic-based black paint and EGaIn liquid metal (LM) microdroplets, serves as an excellent absorber for efficiently converting near-infrared (NIR) irradiation into heat for actuating liquid-crystal elastomer (LCE) actuators. The introduction of LM microdroplets into the PTFs effectively increases the overall thermal efficiency of PTFs. Miniaturized soft crawlers monolithically integrated with the NIR-driven LCE actuators are also implemented for demonstrating the application of the proposed PTF. The crawler’s locomotion, which is inspired by the rectilinear movement of snakes, is generated with the proposed PTF for inducing the LC-to-isotropic phase transition of the LCEs. The experimental results show that introducing LM microdroplets into the PTF can effectively reduce the thermal time constants of LCE actuators by 70%. Under periodic on/off NIR illumination cycles, the locomotion of crawlers with different dimensions is also demonstrated. The measurement results indicate that the proposed PTF is not only essential for enabling photothermal LCE actuation but also quite efficient and durable for repeated operation.

Transient response and domain formation in electrically deforming liquid crystal networks

Recently, three distinct, well-separated transient regimes were discovered in the dynamics of the volume expansion of shape-shifting liquid crystal network films in response to the switching on of an alternating electric field [Van der Kooij et al., Nat. Commun., 2019, 10, 1]. Employing a spatially resolved, time-dependent Landau theory that couples local volume generation to the degree of orientational order of mesogens that are part of a viscoelastic network, we are able to offer a physical explanation for the existence of three time scales. We find that the initial response is dominated by overcoming the impact of thermal noise, after which the top of the film expands, followed by a permeation of this response into the bulk region. An important signature of our predictions is a significant dependence of the three time scales on the film thickness, where we observe a clear thin-film-to-bulk transition. The point of transition coincides with the emergence of spatial inhomogeneities in the bulk of the film in the form of domains separated by regions of suppressed expansion. This ultimately gives rise to variations in the steady-state overall expansion of the film and may lead to uncontrolled patterning. According to our model, domain formation can be suppressed by (1) decreasing the thickness of the as-prepared film, (2) increasing the linear dimensions of the mesogens, or (3) their degree of orientational order when cross-linked into the network. Our findings provide a handle to achieve finer control over the actuation of smart liquid crystal network coatings.

Rheology of liquid crystalline oligomers for 3-D printing of liquid crystalline elastomers

Liquid crystalline monomers can be oligomerized and subsequently 3-D printed to prepare liquid crystalline elastomers (LCEs) with spatial variation of the nematic director to create soft materials that undergo complex shape change when subject to stimulus. Here, we detail the correlation of alignment in 3-D printed LCE on the shear history of the oligomeric ink. This coupling is evident both in the polymerization of sheared LCE samples as well as steady-state rheological experiments that quantify the time-dependent flow behaviors of these complex fluids. Under a steady shear flow, oligomeric LC inks transition from a nematic state with unaligned (polydomain) orientation to a uniaxially aligned (monodomain) nematic phase over a large range of applied strain. After cessation of shear flow, the oligomeric LC inks return the polydomain orientation over approximately 30 minutes. The alignment of liquid crystalline segments in the LCE (and the associated stimuli-response of the materials) is ultimately correlated to the degree of strain applied to the ink.

Liquid Crystalline Elastomers Based on Click Chemistry

Liquid crystalline elastomers (LCEs) have emerged as an important class of functional materials that are suitable for a wide range of applications, such as sensors, actuators, and soft robotics. The unique properties of LCEs originate from the combination between liquid crystal and elastomeric network. The control of macroscopic liquid crystalline orientation and network structure is crucial to realizing the useful functionalities of LCEs. A variety of chemistries have been developed to fabricate LCEs, including hydrosilylation, free radical polymerization of acrylate, and polyaddition of epoxy and carboxylic acid. Over the past few years, the use of click chemistry has become a more robust and energy-efficient way to construct LCEs with desired structures. This article provides an overview of emerging LCEs based on click chemistries, including aza-Michael addition between amine and acrylate, radical-mediated thiol-ene and thiol-yne reactions, base-catalyzed thiol-acrylate and thiol-epoxy reactions, copper-catalyzed azide-alkyne cycloaddition, and Diels-Alder cycloaddition. The similarities and differences of these reactions are discussed, with particular attention focused on the strengths and limitations of each reaction for the preparation of LCEs with controlled structures and orientations. The compatibility of these reactions with the traditional and emerging processing techniques, such as surface alignment and additive manufacturing, are surveyed. Finally, the challenges and opportunities of using click chemistry for the design of LCEs with advanced functionalities and applications are discussed.

Nematic Templated Complex Nanofiber Structures by Projection Display

Oriented arrays of nanofibers are ubiquitous in nature and have been widely used in recreation of the biological functions such as bone and muscle tissue regenerations. However, it remains a challenge to produce nanofiber arrays with a complex organization by using current fabrication techniques such as electrospinning and extrusion. In this work, we propose a method to fabricate the complex organization of nanofiber structures templated by a spatially varying ordered liquid crystal host, which follows the pattern produced by a maskless projection display system. By programming the synchronization of the rotated polarizer and projected segments with different shapes, various configurations of nanofiber organization ranging from a single to two-dimensional lattice of arbitrary topological defects are created in a deterministic manner. The nanofiber arrays can effectively guide and promote neurite outgrowth. The application of nanofibers with arced profiles and topological defects on neural tissue organization is also demonstrated. This finding, combined with the versatility and programmability of nanofiber structures, suggests that they will help solve challenges in nerve repair, neural regeneration, and other related tissue engineering fields.

Photoinduced deformation of amorphous polyimide enabled by an improved azobenzene isomerization efficiency

A newly designed azo-PI, without pre-stretching or polarized-light irradiation, exhibits reversible bending behaviors under alternate UV and visible light irradiation, providing a facile route to deformable 2D/3D structure actuators.

Controlling permeation in electrically deforming liquid crystal network films: A dynamical Landau theory

Liquid crystal networks exploit the coupling between the responsivity of liquid crystalline mesogens, e.g., to electric fields, and the (visco)elastic properties of a polymer network. Because of this, these materials have been put forward for a wide array of applications, including responsive surfaces such as artificial skins and membranes. For such applications, the desired functional response must generally be realized under strict geometrical constraints, such as provided by supported thin films. To model such settings, we present a dynamical, spatially heterogeneous Landau-type theory for electrically actuated liquid crystal network films. We find that the response of the liquid crystal network permeates the film from top to bottom, and illustrate how this affects the timescale associated with macroscopic deformation. Finally, by linking our model parameters to experimental quantities, we suggest that the permeation rate can be controlled by varying the aspect ratio of the mesogens and their degree of orientational order when crosslinked into the polymer network, for which we predict a single optimum. Our results contribute specifically to the rational design of future applications involving transport or on-demand release of molecular cargo in liquid crystal network films.

Light-Actuated Liquid Crystal Elastomer Prepared by Projection Display

Soft materials with programmability have been widely used in drug delivery, tissue engineering, artificial muscles, biosensors, and related biomedical engineering applications. Liquid crystal elastomers (LCEs) can easily morph into three-dimensional (3D) shapes by external stimuli such as light, heat, and humidity. In order to program two-dimensional (2D) LCE sheets into desired 3D morphologies, it is critical to precisely control the molecular orientations in LCE. In this work, we propose a simple photopatterning method based on a maskless projection display system to create spatially varying molecular orientations in LCE films. By designing different synchronized rotations of the polarizer and projected images, diverse configurations ranging from individual to 2D lattice of topological defects are fabricated. The proposed technique significantly simplified the photopatterning procedure without using fabricated masks or waveplates. Shape transformations such as a cone and a truncated square pyramid, and functionality mimicking the responsive Mimosa Pudica are demonstrated in the fabricated LCE films. The programmable LCE morphing behaviors demonstrated in this work will open opportunities in soft robotics and smart functional devices.

Photopatterning Crystal Orientation in Shape-Morphing Polymers

Shape-morphing polymers have gained particular attention due to their unique capability of shape transformation under numerous external stimuli such as light, pH, and temperature. Their shape-morphing properties can be used in various applications such as robotics, artificial muscles, and biomedical devices. To take advantage of the stimuli-responsive properties of the smart polymers in such applications, programming shape change precisely through a facile synthetic procedure is essential. Programmable shape-morphing is readily obtained in hydrogels and liquid crystal polymer networks, but shape programming of semicrystalline polymers usually relies on low-resolution mechanical deformation. In this paper, a semicrystalline shape-morphing polymer with a controlled shape programmability was developed via photopatterning crystal orientation using a spatially controlled photopolymerization technique. The semicrystalline polymer network forms aligned crystallites at the boundaries between dark and bright regions during photopolymerization using a projector, which introduces an anisotropic stimulus response in the films. The semicrystalline polymer films with photoaligned crystallites expand 9-15% in the direction perpendicular to the patterned lines when heated above the melting temperature. Furthermore, spatially patterning the crystal orientation enables the formation of various complex 3D structures including a helical coil, a coil with a handedness inversion, a cone, a saddle, and a twisting flower. Finally, the magnitude of the shape transformation was controlled by varying the polymerization temperatures, and the actuation temperature was tuned by changing the amount of crystallinity in the polymer films. The simplicity and ease of control of our approach to program complex 3D structures from 2D semicrystalline polymer films make it a promising system for the aforementioned applications.

Intermolecular Interactions and Intramolecular Motions in Photomechanical Effect: Nonlinear Thermo- and Photomechanical Behaviors of Azobenzene-Functionalized Amide-Imide Block Copolymers

To discern multiple intertwined effects, a set of azobenzene-functionalized amide-imide block copolymers, azo(PA-co-PI)-x, where x is amide-block content, viz., [azoPA] = 25, 50, 75 mol %, was synthesized from 2,2-bis{4-[4-(4-aminophenyldiazenyl)phenoxy]phenyl}propane(azoBPA), 4,4'-oxydibenzoyl chloride (ODBC), and 4,4'-oxydiphthalic anhydride (OPDA). Including homopolymers (azoPA and azoPI), this series of amorphous azopolymers possesses a high glass-transition temperature (T_g > 210 °C) and a modulus (E' ∼ 1.23-2.50 GPa). Their photobending (ca. 23-90°) and photostress (ca. 250-380 kPa) were assessed in the form of cantilevers with a linearly polarized 445 nm light. Nonlinear composition/[azoPA] dependencies of the thermo- and photomechanical properties are correlated. As [azoPA] increases from 0 mol %; T_g, E', photostress, and photobending angle initially decrease to reach four separate minima for azo(PA-co-PI)-50; and then all increase with a higher [azoPA]. The trend considerations of film density, dynamic thermomechanical, Fourier transform infrared (FT-IR), and ultraviolet-visible (UV-vis) measurements implicate that (i) intermolecular association and intramolecular segmental mobility collectively influence the photomechanical outcomes and (ii) two types of hydrogen bonding (HB), namely, amide-amide [HB-AA] and amide-imide [HB-AI] coexist in azo(PA-co-PI)-x copolymers, with [HB-AI] being largely responsible for photomechanical outcomes of azo(PA-co-PI)-x with [azoPA] <40-50 mol %, and [HB-AA] for [azoPA] >40-50 mol %. We hypothesize that the "U-shaped" photomechanical effect apparently stems from the cooperative "unzipping" of H bonds in the [HB-AA]* excited state with H bonds in [HB-AI]* being stabilized by electrostatic interactions inherent in an excited intermolecular complex.

Shape-programmable liquid crystal elastomer structures with arbitrary three-dimensional director fields and geometries

Liquid crystal elastomers exhibit large reversible strain and programmable shape transformations, enabling various applications in soft robotics, dynamic optics, and programmable origami and kirigami. The morphing modes of these materials depend on both their geometries and director fields. In two dimensions, a pixel-by-pixel design has been accomplished to attain more flexibility over the spatial resolution of the liquid crystal response. Here we generalize this idea in two steps. First, we create independent, cubic light-responsive voxels, each with a predefined director field orientation. Second, these voxels are in turn assembled to form lines, grids, or skeletal structures that would be rather difficult to obtain from an initially connected material sample. In this way, the orientation of the director fields can be made to vary at voxel resolution to allow for programmable optically- or thermally-triggered anisotropic or heterogeneous material responses and morphology changes in three dimensions that would be impossible or hard to implement otherwise.

Buckling-Fracture Transition and the Geometrical Charge of a Crack

We present a unifying approach that describes both surface bending and fracture in the same geometrical framework. An immediate outcome of this view is a prediction for a new mechanical transition: the buckling-fracture transition. Using responsive gel strips that are subjected to nonuniform osmotic stress, we show the existence of the transition: Thin plates do not fracture. Instead, they release energy via buckling, even at strains that can be orders of magnitude larger than the Griffith fracture criterion. The analysis of the system reveals the dependence of the transition on system's parameters and agrees well with experimental results. Finally, we suggest a new description of a mode I crack as a line distribution of Gaussian curvature. It is thus exchangeable with extrinsic generation of curvature via buckling. The work opens the way for the study of mechanical problems within a single nonlinear framework. It suggests that fracture driven by internal stresses can be completely avoided by a proper geometrical design.

Hydrogen-Bonded Supramolecular Liquid Crystal Polymers: Smart Materials with Stimuli-Responsive, Self-Healing, and Recyclable Properties

Hydrogen-bonded liquid crystalline polymers have emerged as promising “smart” supramolecular functional materials with stimuli-responsive, self-healing, and recyclable properties. The hydrogen bonds can either be used as chemically responsive (i.e., pH-responsive) or as dynamic structural (i.e., temperature-responsive) moieties. Responsiveness can be manifested as changes in shape, color, or porosity and as selective binding. The liquid crystalline self-organization gives the materials their unique responsive nanostructures. Typically, the materials used for actuators or optical materials are constructed using linear calamitic (rod-shaped) hydrogen-bonded complexes, while nanoporous materials are constructed from either calamitic or discotic (disk-shaped) complexes. The dynamic structural character of the hydrogen bond moieties can be used to construct self-healing and recyclable supramolecular materials. In this review, recent findings are summarized, and potential future applications are discussed.

Reversible Curvature Reversal of Monolithic Liquid Crystal Elastomer Film and Its Smart Valve Application

Beyond a traditional stimuli-responsive soft actuator that shows a single motion by a stimulus, multidirectional actuation reversal with a single stimulus is highly required in applications such as shape morphing sensors and soft robotics. Liquid crystal elastomers (LCEs) are one of the most attractive candidates for the soft actuator due to their capability of stimuli-responsive shape changing in 3D, which is programmable with local orientation of LC mesogens. Here, a simple but effective method to fabricate monolithic LCE actuators that are capable of reversible curvature reversal in bending and twisting deformation by a single stimulus-heat-is reported. The curvature reversal of the LCE film can be programmed by means of asymmetric crosslinking density along the thickness and the orientation of the LC mesogens. The curvature reversal of the monolithic LCE film exhibits highly reversible (more than 100 times) and fast actuation (≈3-5 s) by heating and cooling, allowing new concept of a practical application using LCE material: a self-regulated smart valve that is capable of qualitatively sorting liquids by temperature. It is believed that this system is potentially applied to a self-regulated sorting platform for various endothermic and exothermic chemical or biological reactions.

Programmable Liquid Crystal Defect Arrays via Electric Field Modulation for Mechanically Functional Liquid Crystal Networks

The arrangement of mesogenic units determines mechanical response of the liquid crystal polymer network (LCN) film to heat. Here, we show an interesting approach to programming three-dimensional patterns of the LCN films with periodic topological defects generated by applying an electric field. The mechanical properties of three representative patterned LCN films were investigated in terms of the arrangement of mesogenic units through tensile testing. Remarkably, it was determined that LCN films showed enhanced toughness and ductility as defects increased in a given area, which is related to the elastic modulus mismatch that mitigates crack propagation. Our platform can also be used to modulate the frictional force of the patterned LCN films by varying the temperature, which can provide insight into the multiplex mechanical properties of LCN films.

Design of nematic liquid crystals to control microscale dynamics

The dynamics of small particles, both living such as swimming bacteria and inanimate, such as colloidal spheres, has fascinated scientists for centuries. If one could learn how to control and streamline their chaotic motion, that would open technological opportunities in the transformation of stored or environmental energy into systematic motion, with applications in micro-robotics, transport of matter, guided morphogenesis. This review presents an approach to command microscale dynamics by replacing an isotropic medium with a liquid crystal. Orientational order and associated properties, such as elasticity, surface anchoring, and bulk anisotropy, enable new dynamic effects, ranging from the appearance and propagation of particle-like solitary waves to self-locomotion of an active droplet. By using photoalignment, the liquid crystal can be patterned into predesigned structures. In the presence of the electric field, these patterns enable the transport of solid and fluid particles through nonlinear electrokinetics rooted in anisotropy of conductivity and permittivity. Director patterns command the dynamics of swimming bacteria, guiding their trajectories, polarity of swimming, and distribution in space. This guidance is of a higher level of complexity than a simple following of the director by rod-like microorganisms. Namely, the director gradients mediate hydrodynamic interactions of bacteria to produce an active force and collective polar modes of swimming. The patterned director could also be engraved in a liquid crystal elastomer. When an elastomer coating is activated by heat or light, these patterns produce a deterministic surface topography. The director gradients define an activation force that shapes the elastomer in a manner similar to the active stresses triggering flows in active nematics. The patterned elastomer substrates could be used to define the orientation of cells in living tissues. The liquid-crystal guidance holds a major promise in achieving the goal of commanding microscale active flows.

Elastomeric nematic colloids, colloidal crystals and microstructures with complex topology

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.

Combined coarse-grained molecular dynamics and finite-element study of light-activated deformation of photoresponsive polymers

The azobenzene-containing crosslinked liquid crystalline polymer is a potential candidate for a stimuli-responsive soft robot, as it provides contactless actuation without the implementation of any separate component. For facilitating practical applications of this novel material, complicated and predefined motions have been realized by tailoring the chemical structure of the polymer network. However, conventional multiscale mechanical analysis, which utilizes the all-atom molecular dynamics to represent a microscopic model, is unsuitable for handling diverse material design parameters due to excessive computational costs. Hence, a multiscale optomechanical simulation framework, which combines the coarse-grained molecular dynamics (CG MD) and the finite-element (FE) method, is developed in this study. The CG MD simulation satisfactorily reproduces the light-induced phase transition and photosoftening effect on the mechanical properties. In particular, using the mesoscale analysis, the presented methodology can treat diverse morphology parameters (liquid crystal phase, spacer length, and crosslinking density) to observe the associated photodeformations. The photostrain and elastic modulus profiles in terms of photoisomerization ratio are implemented into the continuum-scale governing equation, which is based on the neoclassical elasticity theory. To efficiently reflect the light-induced large rotations of liquid crystal mesogens and the corresponding geometric nonlinearity, a corotational formulation is employed in the FE shell model. We examine the mesostructural-morphology-dependent photobending deformations of the nematic and smectic photoresponsive polymers (PRPs). In addition, the mesoscopic-texture-mediated unique 3D deformations are investigated by modeling the topological defects. This study offers insight into the engineering of PRP materials for designing the mechanical motions of smart actuators.

Defective nematogenesis: Gauss curvature in programmable shape-responsive sheets with topological defects

Flat sheets encoded with patterns of contraction/elongation morph into curved surfaces. If the surfaces bear Gauss curvature, the resulting actuation can be strong and powerful. We deploy the Gauss-Bonnet theorem to deduce the Gauss curvature encoded in a pattern of uniform-magnitude contraction/elongation with spatially varying direction, as is commonly implemented in patterned liquid crystal elastomers. This approach reveals two fundamentally distinct contributions: a structural curvature which depends on the precise form of the pattern, and a topological curvature generated by defects in the contractile direction. These curvatures grow as different functions of the contraction/elongation magnitude, explaining the apparent contradiction between previous calculations for simple +1 defects, and smooth defect-free patterns. We verify these structural and topological contributions by conducting numerical shell calculations on sheets encoded with simple higher-order contractile defects to reveal their activated morphology. Finally we calculate the Gauss curvature generated by patterns with spatially varying magnitude and direction, which leads to additional magnitude gradient contributions to the structural term. We anticipate this form will be useful whenever magnitude and direction are natural variables, including in describing the contraction of a muscle along its patterned fiber direction, or a tissue growing by elongating its cells.

Self-Oscillating Membranes: Chemomechanical Sheets Show Autonomous Periodic Shape Transformation

While living organisms have mastered the dynamic control of residual stresses within sheets to induce shape transformation and locomotion, man-made implementations are rudimentary. We present the first autonomously shape-shifting sheets made of a gel that shrinks and swells in response to the phase of an oscillatory chemical (Belousov-Zhabotinsky) reaction. Propagating reaction-diffusion fronts induce localized deformation of the gel. We show that these localized deformations prescribe a spatiotemporal pattern of Gaussian curvature, leading to time-periodic global shape changes. We present the computational tools and experimental protocols needed to control this system, principally the relationship between the Gaussian curvature and the reaction phase, and optical imprinting of the wave pattern. Together, our results demonstrate a route for developing fully autonomous soft machines mimicking some of the locomotive capabilities of living organisms.

Review: knots and other new topological effects in liquid crystals and colloids

Humankind has been obsessed with knots in religion, culture and daily life for millennia, while physicists like Gauss, Kelvin and Maxwell already involved them in models centuries ago. Nowadays, colloidal particles can be fabricated to have shapes of knots and links with arbitrary complexity. In liquid crystals, closed loops of singular vortex lines can be knotted by using colloidal particles and laser tweezers, as well as by confining nematic fluids into micrometer-sized droplets with complex topology. Knotted and linked colloidal particles induce knots and links of singular defects, which can be interlinked (or not) with colloidal particle knots, revealing the diversity of interactions between topologies of knotted fields and topologically nontrivial surfaces of colloidal objects. Even more diverse knotted structures emerge in nonsingular molecular alignment and magnetization fields in liquid crystals and colloidal ferromagnets. The topological solitons include hopfions, skyrmions, heliknotons, torons and other spatially localized continuous structures, which are classified based on homotopy theory, characterized by integer-valued topological invariants and often contain knotted or linked preimages, nonsingular regions of space corresponding to single points of the order parameter space. A zoo of topological solitons in liquid crystals, colloids and ferromagnets promises new breeds of information displays and a plethora of data storage, electro-optic and photonic applications. Their particle-like collective dynamics echoes coherent motions in active matter, ranging from crowds of people to schools of fish. This review discusses the state of the art in the field, as well as highlights recent developments and open questions in physics of knotted soft matter. We systematically overview knotted field configurations, the allowed transformations between them, their physical stability and how one can use one form of knotted fields to model, create and imprint other forms. The large variety of symmetries accessible to liquid crystals and colloids offer insights into stability, transformation and emergent dynamics of fully nonsingular and singular knotted fields of fundamental and applied importance. The common thread of this review is the ability to experimentally visualize these knots in real space. The review concludes with a discussion of how the studies of knots in liquid crystals and colloids can offer insights into topologically related structures in other branches of physics, with answers to many open questions, as well as how these experimentally observable knots hold a strong potential for providing new inspirations to the mathematical knot theory.

3D Microstructures of Liquid Crystal Networks with Programmed Voxelated Director Fields

The shape-shifting behavior of liquid crystal networks (LCNs) and elastomers (LCEs) is a result of an interplay between their initial geometrical shape and their molecular alignment. For years, reliance on either one-step in situ or two-step film processing techniques has limited the shape-change transformations from 2D to 3D geometries. The combination of various fabrication techniques, alignment methods, and chemical formulations developed in recent years has introduced new opportunities to achieve 3D-to-3D shape-transformations in large scales, albeit the precise control of local molecular alignment in microscale 3D constructs remains a challenge. Here, the voxel-by-voxel encoding of nematic alignment in 3D microstructures of LCNs produced by two-photon polymerization using high-resolution topographical features is demonstrated. 3D LCN microstructures (suspended films, coils, and rings) with designable 2D and 3D director fields with a resolution of 5 µm are achieved. Different shape transformations of LCN microstructures with the same geometry but dissimilar molecular alignments upon actuation are elicited. This strategy offers higher freedom in the shape-change programming of 3D LCN microstructures and expands their applicability in emerging technologies, such as small-scale soft robots and devices and responsive surfaces.

Evolving, complex topography from combining centers of Gaussian curvature

Liquid crystal elastomers and glasses can have significant shape change determined by their director patterns. Cones deformed from circular director patterns have nontrivial Gaussian curvature localized at tips, curved interfaces, and intersections of interfaces. We employ a generalized metric compatibility condition to characterize two families of interfaces between circular director patterns, hyperbolic and elliptical interfaces, and find that the deformed interfaces are geometrically compatible. We focus on hyperbolic interfaces to design complex topographies and nonisometric origami, including n-fold intersections, symmetric and irregular tilings. The large design space of threefold and fourfold tiling is utilized to quantitatively inverse design an array of pixels to display target images. Taken together, our findings provide comprehensive design principles for the design of actuators, displays, and soft robotics in liquid crystal elastomers and glasses.

Liquid-Crystal-Mediated Geometric Phase: From Transmissive to Broadband Reflective Planar Optics

Planar optical elements that can manipulate the multidimensional physical parameters of light efficiently and compactly are highly sought after in modern optics and nanophotonics. In recent years, the geometric phase, induced by the photonic spin-orbit interaction, has attracted extensive attention for planar optics due to its powerful beam shaping capability. The geometric phase can usually be generated via inhomogeneous anisotropic materials, among which liquid crystals (LCs) have been a focus. Their pronounced optical properties and controllable and stimuli-responsive self-assembly behavior introduce new possibilities for LCs beyond traditional panel displays. Recent advances in LC-mediated geometric phase planar optics are briefly reviewed. First, several recently developed photopatterning techniques are presented, enabling the accurate fabrication of complicated LC microstructures. Subsequently, nematic LC-based transmissive planar optical elements and chiral LC-based broadband reflective elements are reviewed systematically. Versatile functionalities are revealed, from conventional beam steering and focusing, to advanced structuring. Combining the geometric phase with structured LC materials offers a satisfactory platform for planar optics with desired functionalities and drastically extends exceptional applications of ordered soft matter. Some prospects on this rapidly advancing field are also provided.

Materials as Machines

Machines are systems that harness input power to extend or advance function. Fundamentally, machines are based on the integration of materials with mechanisms to accomplish tasks-such as generating motion or lifting an object. An emerging research paradigm is the design, synthesis, and integration of responsive materials within or as machines. Herein, a particular focus is the integration of responsive materials to enable robotic (machine) functions such as gripping, lifting, or motility (walking, crawling, swimming, and flying). Key functional considerations of responsive materials in machine implementations are response time, cyclability (frequency and ruggedness), sizing, payload capacity, amenability to mechanical programming, performance in extreme environments, and autonomy. This review summarizes the material transformation mechanisms, mechanical design, and robotic integration of responsive materials including shape memory alloys (SMAs), piezoelectrics, dielectric elastomer actuators (DEAs), ionic electroactive polymers (IEAPs), pneumatics and hydraulics systems, shape memory polymers (SMPs), hydrogels, and liquid crystalline elastomers (LCEs) and networks (LCNs). Structural and geometrical fabrication of these materials as wires, coils, films, tubes, cones, unimorphs, bimorphs, and printed elements enables differentiated mechanical responses and consistently enables and extends functional use.

Electroplasticization of Liquid Crystal Polymer Networks

Shape-shifting liquid crystal networks (LCNs) can transform their morphology and properties in response to external stimuli. These active and adaptive polymer materials can have impact in a diversity of fields, including haptic displays, energy harvesting, biomedicine, and soft robotics. Electrically driven transformations in LCN coatings are particularly promising for application in electronic devices, in which electrodes are easily integrated and allow for patterning of the functional response. The morphing of these coatings, which are glassy in the absence of an electric field, relies on a complex interplay between polymer viscoelasticity, liquid crystal order, and electric field properties. Morphological transformations require the material to undergo a glass transition that plasticizes the polymer sufficiently to enable volumetric and shape changes. Understanding how an alternating current can plasticize very stiff, densely cross-linked networks remains an unresolved challenge. Here, we use a nanoscale strain detection method to elucidate this electric-field-induced devitrification of LCNs. We find how a high-frequency alternating field gives rise to pronounced nanomechanical changes at a critical frequency, which signals the electrical glass transition. Across this transition, collective motion of the liquid crystal molecules causes the network to yield from within, leading to network weakening and subsequent nonlinear expansion. These results unambiguously prove the existence of electroplasticization. Fine-tuning the induced emergence of plasticity will not only enhance the surface functionality but also enable more efficient conversion of electrical energy into mechanical work.

Toward Programmed Complex Stress-Induced Mechanical Deformations of Liquid Crystal Elastomers

We prepare a liquid crystal elastomer (LCE) with a spatially patterned liquid crystal director field from an all-acrylate LCE. Mechanical deformations of this material lead to a complex and spatially varying deformation with localised body rotations, shears and extensions. Together, these dictate the evolved shape of the deformed film. Using polarising microscopy, we map the local rotation of the liquid crystal director in Eulerian and Lagrangian frames and use these to determine rules for programming complex, stress-induced mechanical shape deformations of LCEs. Moreover, by applying a recently developed empirical model for the mechanical behaviour of our LCE, we predict the non-uniform stress distributions in our material. These results show the promise of empirical approaches to modelling the anisotropic and nonlinear mechanical responses of LCEs which will be important as the community moves toward realising real-world, LCE-based devices.

Mechanically programmed 2D and 3D liquid crystal elastomers at macro- and microscale via two-step photocrosslinking

Liquid crystal elastomers (LCEs) are a unique class of active materials with the largest known reversible shape transformation in the solid state. The shape change of LCEs is directed by programming their molecular orientation, and therefore, several strategies to control LC alignment have been developed. Although mechanical alignment coupled with a two-step crosslinking is commonly adopted for uniaxially-aligned monodomain LCE synthesis, the fabrication of 3D-shaped LCEs at the macro- and microscale has been rarely accomplished. Here, we report a facile processing method for fabricating 2D and 3D-shaped LCEs at the macro- and microscales at room temperature by mechanically programming (i.e., stretching, pressing, embossing and UV-imprinting) the polydomain LCE, and subsequent photocrosslinking. The programmed LCEs exhibited a reversible shape change when exposed to thermal and chemical stimuli. Besides the programmed shape changes, the actuation strain can also be preprogrammed by adjusting the extent of elongation of a polydomain LCE. Furthermore, the LCE micropillar arrays prepared by UV-imprinting displayed a substantial change in pillar height in a reversible manner during thermal actuation. Our convenient method for fabricating reversible 2D and 3D-shaped LCEs from commercially available materials may expedite the potential applications of LCEs in actuators, soft robots, smart coatings, tunable optics and medicine.

Liquid crystalline networks based on photo-initiated thiol-ene click chemistry

Photo-initiated thiol-ene click chemistry is used to develop shape memory liquid crystalline networks (LCNs). A biphenyl-based di-vinyl monomer is synthesized and cured with a di-thiol chain extender and a tetra-thiol crosslinker using UV light. The effects of photo-initiator concentration and UV light intensity on the curing behavior and liquid crystalline (LC) properties of the LCNs are investigated. The chemical composition is found to significantly influence the microstructure and the related thermomechanical properties of the LCNs. The structure-property relationship is further explored using molecular dynamics simulations, revealing that the introduction of the chain extender promotes the formation of an ordered smectic LC phase instead of agglomerated structures. The concentration of the chain extender affects the liquid crystallinity of the LCNs, resulting in distinct thermomechanical and shape memory properties. This class of LCNs exhibits fast curing rates, high conversion levels, and tailorable liquid crystallinity, making it a promising material system for advanced manufacturing, where complex and highly ordered structures can be produced with fast reaction kinetics and low energy consumption.

Traveling Wave Rotary Micromotor Based on a Photomechanical Response in Liquid Crystal Polymer Networks

The photomechanical response of liquid crystal polymer networks (LCNs) can be used to directly convert light energy into different forms of mechanical energy. In this study, we demonstrate how a traveling deformation, induced in a liquid crystal polymer ring by a spatially modulated laser beam, can be used to drive the ring (the rotor) to rotate around a stationary element (the stator), thus forming a light-powered micromotor. The photomechanical response of the polymer film is modeled numerically, different LCN molecular configurations are studied, and the performance of a 5.5 mm diameter motor is characterized.

Design of Collective Motions from Synthetic Molecular Switches, Rotors, and Motors

Precise control over molecular movement is of fundamental and practical importance in physics, biology, and chemistry. At nanoscale, the peculiar functioning principles and the synthesis of individual molecular actuators and machines has been the subject of intense investigations and debates over the past 60 years. In this review, we focus on the design of collective motions that are achieved by integrating, in space and time, several or many of these individual mechanical units together. In particular, we provide an in-depth look at the intermolecular couplings used to physically connect a number of artificial mechanically active molecular units such as photochromic molecular switches, nanomachines based on mechanical bonds, molecular rotors, and light-powered rotary motors. We highlight the various functioning principles that can lead to their collective motion at various length scales. We also emphasize how their synchronized, or desynchronized, mechanical behavior can lead to emerging functional properties and to their implementation into new active devices and materials.

Photodeformable Azobenzene-Containing Liquid Crystal Polymers and Soft Actuators

Photodeformable liquid crystal polymers (LCPs) that adapt their shapes in response to light have aroused a dramatic growth of interest in the past decades, since light as a stimulus enables the remote control and diverse deformations of materials. This review focuses on the growing research on photodeformable LCPs, including their basic actuation mechanisms, the various deformation modes, the newly designed molecular structures, and the improvement of processing techniques. Special attention is devoted to the novel molecular structures of LCPs, which allow for easy processing and alignment. The soft actuators with various deformation modes such as bending, twisting, and rolling in response to light are also covered with the emphasis on their photo-induced bionic functions. Potential applications in energy harvesting, self-cleaning surfaces, sensors, and photo-controlled microfluidics are further illustrated. The existing challenges and future directions are discussed at the end of this review.

Morphing of liquid crystal surfaces by emergent collectivity

Liquid crystal surfaces can undergo topographical morphing in response to external cues. These shape-shifting coatings promise a revolution in various applications, from haptic feedback in soft robotics or displays to self-cleaning solar panels. The changes in surface topography can be controlled by tailoring the molecular architecture and mechanics of the liquid crystal network. However, the nanoscopic mechanisms that drive morphological transitions remain unclear. Here, we introduce a frequency-resolved nanostrain imaging method to elucidate the emergent dynamics underlying field-induced shape-shifting. We show how surface morphing occurs in three distinct stages: (i) the molecular dipoles oscillate with the alternating field (10-100 ms), (ii) this leads to collective plasticization of the glassy network (~1 s), (iii) culminating in actuation of the topography (10-100 s). The first stage appears universal and governed by dielectric coupling. By contrast, yielding and deformation rely on a delicate balance between liquid crystal order, field properties and network viscoelasticity.

Nonsphere Drop Impact Assembly of Graphene Oxide Liquid Crystals

Creating long-lived topological textured liquid crystals (LCs) in confined nonspherical space is of significance in both generations of structures and fundamental studies of topological physics. However, it remains a great challenge due to the fluid character of LCs and the unstable tensional state of transient nonspheres. Here, we realize a rich series of topological textures confined in nonspherical geometries by drop impact assembly (DIA) of graphene oxide (GO) aqueous LCs. Various highly curved nonspherical morphologies of LCs were captured by gelator bath, generating distinct out-of-equilibrium yet long-lived macroscopic topological textures in 3D confinement. Our hydrodynamic investigations on DIA processes reveal that the shear-thinning fluid behavior of LCs and the arrested GO alignments mainly contribute to the topological richness in DIA. Utilizing the shaping behavior of GO LCs compared to other conventional linear polymers such as alginate, we further extend the DIA methodology to design more complex yet highly controllable functional composites and hybrids. This work thus reveals the potential to scale production of uniform yet anisotropic materials with rich topologic textures and tailored composition.

Photoswitchable chevron topographies of glassy nematic coatings

We report a strategy to create photoswitchable chevron topographies via buckling of glassy nematic coatings with zigzag director alignments on soft elastic substrates. The idea is confirmed by numerical simulations where the nonlinear deformation of the coating is modeled by the Föppl-von Kármán plate theory. It is remarkable that the inclination angle of the chevron pattern may deviate significantly from the director orientation and depends on the period of director alignment. Our quantitative analysis shows that the phenomena are caused by in-plane shear stress which alters the direction of maximum principal stress in the coating and decreases monotonically with decreasing period of the director distribution.

Liquid crystal elastomer shell actuators with negative order parameter

Liquid crystals (LCs) are nonsolids with long-range orientational order, described by a scalar order parameter 〈 P 2 〉 = 1 2 〈 3 cos 2 β - 1 〉 . Despite the vast set of existing LC materials, one-third of the order parameter value range, ^-1/₂ < 〈P ₂〉 < 0, has until now been inaccessible. Here, we present the first material with negative LC order parameter in its ground state, in the form of elastomeric shells. The optical and actuation characteristics are opposite to those of conventional LC elastomers (LCEs). This novel class of anti-ordered elastomers gives access to the previously secluded range of liquid crystallinity with 〈P ₂〉 < 0, providing new challenges for soft matter physics and adding a complementary type of LCE actuator that is attractive for applications in, e.g., soft robotics.