Giant lateral electrostriction in ferroelectric liquid-crystalline elastomers

Durable liquid-crystalline vitrimer actuators

Vitrimer-based liquid-crystalline elastomers (LCEs) exhibit great advantages over the traditional LCEs due to their inherent processability to realize monodomain alignment and construction of LCE actuators with complex 3D structures in a robust way. Though exciting progress has been made, how to achieve a proper balance between processability and actuation durability/stability remains a big challenge. Here, we report a strategy to mitigate the conflict between processability and actuation stability by reducing the catalyst content in an epoxy/acid LCE vitrimer system. With a relatively low catalyst content (0.25 mol% to carboxyl group), monodomain LCEs with large actuation strain (∼95%) and excellent actuation stability (the actuation strain is completely maintained after 100 heating-cooling cycles and more than 90% of the initial strain is retained even after 500 cycles) could be easily prepared. Moreover, the monodomain LCEs can still be readily realigned or directly reconfigured into complex reversible 3D actuators.

Giant Electro-Optical Effect through Electrostriction in a Nanomechanical Metamaterial

Electrostriction is a property of all naturally occurring dielectrics whereby they are mechanically deformed under the application of an electric field. It is demonstrated here that an artificial metamaterial nanostructure comprising arrays of dielectric nanowires, made of silicon and indium tin oxide, is reversibly structurally deformed under the application of an electric field, and that this reconfiguration is accompanied by substantial changes in optical transmission and reflection, thus providing a strong electro-optic effect. Such metamaterials can be used as the functional elements of electro-optic modulators in the visible to near-infrared part of the spectrum. A modulator operating at 1550 nm with effective electrostriction and electro-optic coefficients of order 10^-13 m² V^-2 and 10^-6 m V^-1 , respectively, is demonstrated. Transmission changes of up to 3.5% are obtained with a 500 mV control signal at a modulation frequency of ≈6.5 MHz. With a resonant optical response that can be spectrally tuned by design, modulators based on the artificial electrostrictive effect may be used for laser Q-switching and mode-locking among other applications that require modulation at megahertz frequencies.

Nanoid Canyons On-Demand: Electrically Switchable Surface Topography in Liquid Crystal Networks

Topography is a key factor that governs important properties of surfaces, such as adhesion and wettability, and materials with switchable surface topographies will have switchable surface properties. We demonstrate a principle to generate electrically switchable surface topographies on the surface of a thin nematic liquid crystal elastomer film which is sandwiched between a continuous electrode and a random metal network. Voltage-controlled displacement of the metal network toward the continuous electrode is achieved, resulting in unprecedented topographical modulations in the range of 0-2.5 μm. We show that this depth variation is significantly larger than the expected deformation because of electrostatic attraction between the network and the continuous electrode. This effect is explained by deformation due to the rotation of the liquid crystal side groups along the electric field lines.

Liquid Crystal Elastomers-A Path to Biocompatible and Biodegradable 3D-LCE Scaffolds for Tissue Regeneration

The development of appropriate materials that can make breakthroughs in tissue engineering has long been pursued by the scientific community. Several types of material have been long tested and re-designed for this purpose. At the same time, liquid crystals (LCs) have captivated the scientific community since their discovery in 1888 and soon after were thought to be, in combination with polymers, artificial muscles. Within the past decade liquid crystal elastomers (LCE) have been attracting increasing interest for their use as smart advanced materials for biological applications. Here, we examine how LCEs can potentially be used as dynamic substrates for culturing cells, moving away from the classical two-dimensional cell-culture nature. We also briefly discuss the integration of a few technologies for the preparation of more sophisticated LCE-composite scaffolds for more dynamic biomaterials. The anisotropic properties of LCEs can be used not only to promote cell attachment and the proliferation of cells, but also to promote cell alignment under LCE-stimulated deformation. 3D LCEs are ideal materials for new insights to simulate and study the development of tissues and the complex interplay between cells.

Electroclinic effect in chiral smectic-A liquid crystal elastomers

Chiral smectic-A liquid crystal elastomers are rubbery materials composed of a lamellar arrangement of liquid crystalline mesogens. It has been shown experimentally that these materials shear when subjected to an electric field due to the electrically induced tilt of the director. Experiments have also shown that shearing a chiral smectic-A elastomer gives rise to a polarization. Roughly, the shear force tilts the directors which, in turn, induce electric dipoles. This paper builds on previous works and models the electromechanical response of smectic-A elastomers using free energy contributions that are associated with the lamellar structure, the relative tilt between the director and the layer normal, and the coupling between the director and the electric field. To illustrate the merit of the proposed model, two cases are considered-a deformation induced polarization and an electrically induced deformation. The predictions according to these two models qualitatively agree with experimental findings. Finally, a cylinder composed of helical smectic layers is also considered. It is shown that the electromechanical response varies as a function of the helix angle.

Electro-responsive polyelectrolyte-coated surfaces

The anchoring of polymer chains at solid surfaces is an efficient way to modify interfacial properties like the stability and rheology of colloidal dispersions, lubrication and biocompatibility. Polyelectrolytes are good candidates for the building of smart materials, as the polyion chain conformation can often be tuned by manipulation of different physico-chemical variables. However, achieving efficient and reversible control of this process represents an important technological challenge. In this regard, the application of an external electrical stimulus on polyelectrolytes seems to be a convenient control strategy, for several reasons. First, it is relatively easy to apply an electric field to the material with adequate spatiotemporal control. In addition, in contrast to chemically induced changes, the molecular response to a changing electric field occurs relatively quickly. If the system is properly designed, this response can then be used to control the magnitude of surface properties. In this work we discuss the effect of an external electric field on the adhesion and lubrication properties of several polyelectrolyte-coated surfaces. The influence of the applied field is investigated at different pH and salt conditions, as the polyelectrolyte conformation is sensitive to these variables. We show that it is possible to fine tune friction and adhesion using relatively low applied fields.

Thermal bending coupled with volume change in liquid crystal gels

We investigate the thermal bending behavior of liquid crystal gels with hybrid alignment (H-LCGs) accompanied by volume change in isotropic and nematic solvents. The curvature (r^-1) of H-LCGs in each solvent markedly depends on the temperature (T) in the nematic state including the reversal of the bending direction, as in the case of the corresponding elastomers in the dry state (H-LCE). The thermal bending of three systems-H-LCGs in isotropic and nematic solvents and H-LCE-differs significantly in several aspects including the T range where r^-1 depends on T and the total variation of r^-1. The differences in these features among the three systems result from the differences in the magnitude as well as the T-dependence of the nematic order (S), which is correlated with the T-induced volume change. We demonstrate that the T-dependence of the reduced curvature in each system is satisfactorily described by a combination of linear bending theory and the anisotropic Gaussian network model using the corresponding S-T data.

Soft Actuators for Small-Scale Robotics

This review comprises a detailed survey of ongoing methodologies for soft actuators, highlighting approaches suitable for nanometer- to centimeter-scale robotic applications. Soft robots present a special design challenge in that their actuation and sensing mechanisms are often highly integrated with the robot body and overall functionality. When less than a centimeter, they belong to an even more special subcategory of robots or devices, in that they often lack on-board power, sensing, computation, and control. Soft, active materials are particularly well suited for this task, with a wide range of stimulants and a number of impressive examples, demonstrating large deformations, high motion complexities, and varied multifunctionality. Recent research includes both the development of new materials and composites, as well as novel implementations leveraging the unique properties of soft materials.

Thermomechanical liquid crystalline elastomer capillaries with biomimetic peristaltic crawling function

It is highly desirable to fabricate liquid crystalline elastomer (LCE) devices with novel functions for applications in different areas. In this study, LCE capillaries with biomimetic peristaltic function are fabricated for the first time to mimic the peristaltic crawling locomotion of earthworms. A specifically designed LC cell was prepared for this purpose, which consisted of two coaxial glass capillaries coated with polyimide alignment layers on the inner cell surfaces. The side-on LCE capillaries were fabricated by photoinitiated polymerization/crosslinking of a monomer and a crosslinker in the LC cells. The results show that owing to the effect of the alignment layers on the LC cell walls, the mesogenic units in the network structures are predominantly oriented along the capillary axis. Reversible thermomechanical contraction and expansion are observed for the LCE capillaries, which show a relative contraction of 16% in the length and a relative expansion of 12% in the diameter upon the nematic to isotropic phase transition. When placed in a glass tube with an appropriate inner diameter, reversible peristaltic crawling locomotion of the LCE capillaries is realized by moving a heating source outside the tube along its axis. Under typical conditions, the peristaltic crawling motion shows a moving speed of 0.31 mm s^-1. The mechanism of the peristaltic crawling of the LCE capillary is elucidated with the assistance of the finite elemental analysis (FEA) simulation. A five-stage motion model is established to rationalize these observations and correlate the observations with the crawling locomotion of earthworms. The LCE capillary with the peristaltic crawling locomotion function promises its potential applications in biomimetic miniature robots and actuators.

Electroactive polymers for sensing

Electromechanical coupling in electroactive polymers (EAPs) has been widely applied for actuation and is also being increasingly investigated for sensing chemical and mechanical stimuli. EAPs are a unique class of materials, with low-moduli high-strain capabilities and the ability to conform to surfaces of different shapes. These features make them attractive for applications such as wearable sensors and interfacing with soft tissues. Here, we review the major types of EAPs and their sensing mechanisms. These are divided into two classes depending on the main type of charge carrier: ionic EAPs (such as conducting polymers and ionic polymer–metal composites) and electronic EAPs (such as dielectric elastomers, liquid-crystal polymers and piezoelectric polymers). This review is intended to serve as an introduction to the mechanisms of these materials and as a first step in material selection for both researchers and designers of flexible/bendable devices, biocompatible sensors or even robotic tactile sensing units.

Mechanoactive materials in cardiac science

Mechanically active biomaterials such as shape memory materials, liquid crystal elastomers, dielectric elastomer actuators, and conductive polymers could be used in mechanical devices to augment heart function or condition cardiac cells and artificial tissues for regenerative medicine solutions.

Synthesis and characterization of chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens

A novel series of siloxane-based chiral smectic side-chain liquid crystalline elastomers containing nematic and chiral mesogens were fabricated through synthesis involving a one-step hydrosilication reaction via a liquid crystalline crosslinking agent containing smectic and nematic phases.

High Dielectric Performance of Polyamide 66/Poly(Vinylidene Fluoride) Flexible Blends Induced by Interfacial Copolymer for Capacitors

The copolymer VAMA was synthesized from vinyl acetic and maleic anhydride. A new all-polymeric blend with a high dielectric constant (ε) has been developed by blending polyvinylidene fluoride (PVDF) with vinyl acetic-maleic anhydride modified polyamide (PA66-g-VM). The blend shows high dielectric constants (εblend = 20) and excellent mechanical properties. The SEM investigations suggest that the enhanced dielectric behavior originates from significant interfacial interactions between polymers. The XRD demonstrates that the compatibilizer affects the crystalline behavior of each component. Furthermore, the stable dielectric constants of the all-polymeric blends can be tuned by adjusting the content of the compatibilizer. The created high-ε all-polymeric blends represent a novel type of material that is technologically simple, easy to process, and of a relatively high dielectric constant, with application for flexible electronics.

Molecular Designs for Enhancement of Polarity in Ferroelectric Soft Materials

The racemic oxovanadium(IV) salmmen complexes, [VO((rac)-(4-X-salmmen))] (X = C₁₂C₁₀C₅ (1), C₁₆ (2), and C₁₈ (3); salmmen = N,N′-monomethylenebis-salicylideneimine) with “banana shaped” molecular structures were synthesized, and their ferroelectric properties were investigated. These complexes exhibit well-defined hysteresis loops in their viscous phases, moreover, 1 also displays liquid crystal behaviour. We observed a synergetic effect influenced by three structural aspects; the methyl substituents on the ethylene backbone, the banana shaped structure and the square pyramidal metal cores all play an important role in generating the observed ferroelectricity, pointing the way to a useful strategy for the creation of advanced ferroelectric soft materials.

Liquid Crystal Elastomer Microspheres as Three-Dimensional Cell Scaffolds Supporting the Attachment and Proliferation of Myoblasts

We report that liquid crystal elastomers (LCEs), often portrayed as artificial muscles, serve as scaffolds for skeletal muscle cell. A simultaneous microemulsion photopolymerization and cross-linking results in nematic LCE microspheres 10-30 μm in diameter that when conjoined form a LCE construct that serves as the first proof-of-concept for responsive LCE muscle cell scaffolds. Confocal microscopy experiments clearly established that LCEs with a globular, porous morphology permit both attachment and proliferation of C2C12 myoblasts, while the nonporous elastomer morphology, prepared in the absence of a microemulsion, does not. In addition, cytotoxicity and proliferation assays confirm that the liquid crystal elastomer materials are biocompatible promoting cellular proliferation without any inherent cytotoxicity.

MoS2 actuators: reversible mechanical responses of MoS2-polymer nanocomposites to photons

New molybdenum disulfide (MoS2)-based polymer composites and their reversible mechanical responses to light are presented, suggesting MoS2 as an excellent candidate for energy conversion. Homogeneous mixtures of MoS2/polydimethylsiloxane (PDMS) nanocomposites (0.1-5 wt.%) were prepared and their near infrared (NIR) mechanical responses studied with increasing pre-strains. NIR triggering resulted in an extraordinary change in stress levels of the actuators by ~490 times. Actuation responses of MoS2 polymer composites depended on applied pre-strains. At lower levels of pre-strains (3-9%) the actuators showed reversible expansion while at high levels (15-50%), the actuators exhibited reversible contraction. An opto-mechanical conversion (η)∼0.5-3 MPa W(-1) was calculated. The ratio of maximum stress due to photo-actuation (σmax) at 50% strain to the minimum stress due to photo-actuation (σmin) at 3% strain was found to be ∼315-322% for MoS2 actuators (for 0.1 to 5 wt.% additive), greater than single layer graphene (∼188%) and multi-wall nanotube (∼172%) photo-mechanical actuators. Unlike other photomechanical actuators, the MoS2 actuators exhibited strong light-matter interactions and an unambiguous increase in amplitude of photomechanical response with increasing strains. A power law dependence of σmax/σmin on strains with a scaling exponent of β = 0.87-1.32 was observed, suggesting that the origin of photomechanical response is intertwined dynamically with the molecular mechanisms at play in MoS2 actuators.

Large-strain, multiform movements from designable electrothermal actuators based on large highly anisotropic carbon nanotube sheets

Many electroactive polymer (EAP) actuators use diverse configurations of carbon nanotubes (CNTs) as pliable electrodes to realize discontinuous, agile movements, for CNTs are conductive and flexible. However, the reported CNT-based EAP actuators could only accomplish simple, monotonous actions. Few actuators were extended to complex devices because efficiently preparing a large-area CNT electrode was difficult, and complex electrode design has not been carried out. In this work, we successfully prepared large-area CNT paper (buckypaper, BP) through an efficient approach. The BP is highly anisotropic, strong, and suitable as flexible electrodes. By means of artful graphic design and processing on BP, we fabricated various functional BP electrodes and developed a series of BP-polymer electrothermal actuators (ETAs). The prepared ETAs can realize various controllable movements, such as large-stain bending (>180°), helical curling (∼ 630°), or even bionic actuations (imitating human-hand actions). These functional and interesting movements benefit from flexible electrode design and the anisotropy of BP material. Owing to the advantages of low driving voltage (20-200 V), electrolyte-free and long service life (over 10000 times), we think the ETAs will have great potential applications in the actuator field.

Poly(vinyl benzoate)-backbone mesogen-jacketed liquid crystalline polymers

This work describes a new system of MJLCPs with poly(vinyl benzoate)-backbone, which are efficiently synthesized by the bulk photo-polymerization method. Furthermore, homogeneous- or homeotropic-aligned cross-linked MJLCP (xMJLCP) films are for the first time successfully prepared.

Side chain liquid crystalline polymers with an optically active polynorbornene backbone and achiral mesogenic side groups

This work describes a series of side-on and end-on SCLCPs with an optically active polynorbornene main chain and achiral mesogens. The side-on SCLCPs tend to form achiral mesophases, while their comparative end-on analogues exhibit chiral mesophases.

Electrically induced deformation in chiral smectic elastomers with different domain structures

Electrical actuation is investigated in two kinds of chiral smectic liquid-crystal elastomers (LCEs) with different domain structures LCE1 and LCE2: The latter is better than the former in orientational order. Tracking fluorescent beads dispersed on the samples enables us to measure the two-dimensional strain tensors in ferroelectric elastomer films. It turns out that the electric-field-induced strain is polarity dependent and the type of molecular orientation responsible for the strain is specified. In LCE1 the shear strain is dominant, whereas in LCE2 it is comparable to the elongation strain, which is explained by the rotation of the principal axes. The essential differences of the two elastomers are observed in the eigenvalues of the strain tensors. The absolute values for LCE1 are larger than those for LCE2. The difference is discussed on the basis of the domain structures.

Electrical Actuation of Cholesteric Liquid Crystal Gels

We demonstrate that the cholesteric liquid crystal (CLC) gels with a global helical variation in their orientation exhibit the pronounced electro-optical and electromechanical effects under an unconstrained geometry. A sufficiently high electric field imposed along the helical axis drives a finite elongation exceeding 30% along the field axis, as well as a finite redshift of the selective reflection band which is opposite to the blueshift often observed for the conventional CLCs and the in situ polymer stabilized CLCs under an electric field.

Higher order harmonic detection for exploring nonlinear interactions with nanoscale resolution

Nonlinear dynamics underpin a vast array of physical phenomena ranging from interfacial motion to jamming transitions. In many cases, insight into the nonlinear behavior can be gleaned through exploration of higher order harmonics. Here, a method using band excitation scanning probe microscopy (SPM) to investigate higher order harmonics of the electromechanical response, with nanometer scale spatial resolution is presented. The technique is demonstrated by probing the first three harmonics of strain for a Pb(Zr(1-x)Ti(x))O₃ (PZT) ferroelectric capacitor. It is shown that the second order harmonic response is correlated with the first harmonic response, whereas the third harmonic is not. Additionally, measurements of the second harmonic reveal significant deviations from Rayleigh-type models in the form of a much more complicated field dependence than is observed in the spatially averaged data. These results illustrate the versatility of n(th) order harmonic SPM detection methods in exploring nonlinear phenomena in nanoscale materials.

Fabrication of highly ordered/switchable polymer nanogratings for nano-actuators using nanoimprint lithography

Polymer micro/nano-actuators are attracting tremendous interest due to their potential applications in micro/nano-mechanical systems and lab-on-a-chip systems. To achieve this, thin films of stimuli-responsive polymers are required to be patterned at the micro/nanometer scale, and also to possess highly ordered orientation in the responsive component. We demonstrate here that nanoscale patterning and uniaxial alignment of liquid crystalline mesogens can be simultaneously achieved by nanoimprint lithography performed in the liquid crystalline mesophase. Photoactive azobenzene mesogens were aligned parallel to the nanogratings imprinted in the films. The degree of alignment depended on the extent of nanoconfinement. The nanogratings expanded in the direction perpendicular to the film upon exposure to uniform UV irradiation, because of trans-to-cis isomerization. In addition, the reversible deformation amplitude strongly depended on the degree of alignment of the photoactive azobenzene mesogens.

Liquid-crystalline ordering as a concept in materials science: from semiconductors to stimuli-responsive devices

While the unique optical properties of liquid crystals (LCs) are already well exploited for flat-panel displays, their intrinsic ability to self-organize into ordered mesophases, which are intermediate states between crystal and liquid, gives rise to a broad variety of additional applications. The high degree of molecular order, the possibility for large scale orientation, and the structural motif of the aromatic subunits recommend liquid-crystalline materials as organic semiconductors, which are solvent-processable and can easily be deposited on a substrate. The anisotropy of liquid crystals can further cause a stimuli-responsive macroscopic shape change of cross-linked polymer networks, which act as reversibly contracting artificial muscles. After illustrating the concept of liquid-crystalline order in this Review, emphasis will be placed on synthetic strategies for novel classes of LC materials, and the design and fabrication of active devices.

Unified molecular field theory of nematic, smectic-A, and smectic-C phases

A unified mean-field molecular theory of nematic (N(U)), smectic A (SmA), and smectic C (SmC) liquid crystal phases, composed of uniaxial nonpolar molecules, is developed taking into account the variation of all orientational and translational order parameters in these phases. Numerical results, obtained by direct global minimization of the free energy, are presented in the form of three typical phase diagrams of different topology. Temperature variation of the relevant order parameters in different sequences of phases is analyzed for various cross sections of the phase diagrams. The present model enables one to reproduce all possible sequences of phase transitions between the given phases including isotropic (Iso)-N(U)-SmA-SmC, Iso-N(U)-SmC, Iso-SmA-SmC, and Iso-SmC. The properties of the NAC point, where the N(U), SmA, and SmC structures coexist, are considered in detail and the shape of the phase diagram in the vicinity of the NAC point is compared with existing experimental data.

Stimuli-responsive transformation in carbon nanotube/expanding microsphere-polymer composites

Our work introduces a class of stimuli-responsive expanding polymer composites with the ability to unidirectionally transform their physical dimensions, elastic modulus, density, and electrical resistance. Carbon nanotubes and core-shell acrylic microspheres were dispersed in polydimethylsiloxane, resulting in composites that exhibit a binary set of material properties. Upon thermal or infrared stimuli, the liquid cores encapsulated within the microspheres vaporize, expanding the surrounding shells and stretching the matrix. The microsphere expansion results in visible dimensional changes, regions of reduced polymeric chain mobility, nanotube tensioning, and overall elastic to plastic-like transformation of the composite. Here, we show composite transformations including macroscopic volume expansion (>500%), density reduction (>80%), and elastic modulus increase (>675%). Additionally, conductive nanotubes allow for remote expansion monitoring and exhibit distinct loading-dependent electrical responses. With the ability to pattern regions of tailorable expansion, strength, and electrical resistance into a single polymer skin, these composites present opportunities as structural and electrical building blocks in smart systems.

Liquid-crystalline elastomer-nanoparticle hybrids with reversible switch of magnetic memory

A stimuli-responsive material is synthesized that combines the actuation potential of liquid-crystalline elastomers with the anisotropic magnetic properties of ellipsoidal iron oxide nanoparticles. The resulting nanocomposite exhibits unique shape-memory features with magnetic information, which can be reversibly stored and erased via parameters typical of soft materials, such as high deformations, low stresses, and liquid-crystalline smectic-isotropic transition temperatures.

Polymersomes with PEG corona: structural changes and controlled release induced by temperature variation

Thermoresponsive behavior of different kinds of polymersomes was studied using small angle neutron scattering (SANS), transmission electron microscopy (TEM), and proton nuclear magnetic resonance ((1)H NMR). The polymersomes were made of block copolymers containing a 2000 Da polyethylene glycol (PEG) as a hydrophilic block and either a liquidlike polymer (e.g., PBA: polybutylacrylate), a solidlike polymer (PS: polystyrene), or a liquid crystalline (LC) polymer as a hydrophobic block. Structural changes in polymersomes are driven in all cases by the critical dehydration temperature of PEG corona, which is closely related to the chemical structure and chain mobility of the hydrophobic block. No structural changes occur upon heating from 25 to 75 °C in the liquidlike polymersomes where the critical dehydration temperature of PEG should be higher than 75 °C. In contrast, glassy PEG-b-PS polymersomes and LC polymersomes show structural changes around 55 °C, which corresponds to the critical dehydration temperature of PEG in those block copolymers. Furthermore, the structural changes depend on the properties of the hydrophobic layer. Glassy PEG-b-PS polymersomes aggregate together above 55 °C, but the bilayer membrane is robust enough to remain intact. This aggregation is reversible, and rather separate polymersomes are recovered upon cooling. However, LC polymersomes display drastic and irreversible structural changes when heated above ∼55 °C. These changes are dependent on the LC structures of the hydrophobic layer. Nematic LC polymersomes turn into thick-walled capsules, whereas smectic LC polymersomes collapse into dense aggregates. As these drastic and irreversible changes decrease or remove the inner compartment volume of the vesicle, LC polymersomes can be used for thermal-responsive controlled release, as shown by a study of calcein release. Finally, toxicity studies proved that LC polymersomes were noncytotoxic and had no effect on cell morphology.

Graphene-nanoplatelet-based photomechanical actuators

This paper reports large light-induced reversible and elastic responses of graphene nanoplatelet (GNP) polymer composites. Homogeneous mixtures of GNP/polydimethylsiloxane (PDMS) composites (0.1-5 wt%) were prepared and their infrared (IR) mechanical responses studied with increasing pre-strains. Using IR illumination, a photomechanically induced change in stress of four orders of magnitude as compared to pristine PDMS polymer was measured. The actuation responses of the graphene polymer composites depended on the applied pre-strains. At low levels of pre-strain (3-9%) the actuators showed reversible expansion while at high levels (15-40%) the actuators exhibited reversible contraction. The GNP/PDMS composites exhibited higher actuation stresses compared to other forms of nanostructured carbon/PDMS composites, including carbon nanotubes (CNTs), for the same fabrication method. An extraordinary optical-to-mechanical energy conversion factor (η(M)) of 7-9 MPa W(-1) for GNP-based polymer composite actuators is reported.