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NoElastocaloric cooling is a promising solid-state alternative to vapor-compression refrigeration. In conventional systems, such as natural rubber, deformation induces entropy change accompanied by temperature release. Unloading the material restores the entropic state and is accompanied by cooling. Inverse elastocaloric effects have been detailed in shape memory alloys, where deformation induces loss of order and cooling. Here, we report on a distinctive inverse elastocaloric effect in liquid crystalline elastomers (LCEs) containing supramolecular hydrogen bonds. Upon deformation, the supramolecular LCE exhibits initial organization but then disorganizes as the intramesogenic hydrogen bonds are broken. Due to the liquid crystalline nature of the dimeric supramolecular bonds, the mechanochemical bond breakage manifests in a disruption in order. By disrupting the extent of liquid crystallinity in the system, we hypothesize that the network disorganizes to the deformation (e.g., entropy increases) and produces an inverse elastocaloric output.t Available 

Cholesteric liquid crystals (CLCs) exhibit Bragg reflection due to their spontaneous self-assembly into a one-dimensional photonic structure. Retaining this cholesteric order in a polymer network requires functionalizing liquid crystals with reactive end groups. However, conventional chemistries for synthesizing cholesteric liquid crystalline polymers often result in poor surface alignment and reduced optical quality. In this work, we investigate a thiol−ene step-growth polymerization approach to fabricate cholesteric liquid crystalline elastomers (CLCEs) with tunable mechanical properties and improved optical quality. By varying the cross-link density, we systematically study the effects on haze, cross-linking degree, and mechanical response. Compared to existing cholesteric liquid crystalline polymers, the thiol−ene-based CLCEs exhibit enhanced surface alignment, reduced haze, and greater mechanical tunability. These materials are further benchmarked against CLCEs synthesized via thiol−acrylate chain transfer polymerization, highlighting the advantages of the thiol−ene reaction for achieving precisely controlled properties in cholesteric polymer networks. 

Liquid crystalline elastomers (LCEs) exhibit reversible macroscopic shape changes in response to a temperature change. Mechanistically, the thermomechanical response of LCEs is associated with the thermotropic nature of the liquid crystalline units (i.e., mesogens) in the polymer network. Upon heating, the mesogen‐mesogen interaction in the LCE is disrupted, which transitions the organization of the polymer network from an ordered to a disordered state. The disruption in order affects the volumetric distribution of macromolecular chains in the polymer network and results in a large directional contraction along the alignment axis. Prior reports detail that the magnitude of actuation depends strongly on the connectivity of LC mesogens (i.e., main‐chain or pendant) within the network. In this study, pendant end‐on mesogens are introduced into a primarily main‐chain supramolecular LCE composition to further reduce crosslink density while preserving overall LC concentration. The introduction of pendant end‐on mesogens to supramolecular LCE compositions further improves thermomechanical properties by enhancing strain‐temperature coupling and reducing actuation temperatures. By systematically varying the concentrations of end‐on and supramolecular mesogens, direct relationships are established between mesogen composition, polymer architecture, and the resulting thermomechanical performance of LCEs. 

Cholesteric liquid crystalline elastomers (CLCEs) exhibit selective reflection due to a periodic variation of the refractive index throughout the thickness of the material. CLCEs can be formulated and prepared to reflect light in the UV, visible, and infrared regions of the electromagnetic spectrum by simply adjusting the concentration of the chiral species. This report details the synthesis and preparation of appropriately thick CLCEs that maximize reflection in both the short-wave and mid-wave infrared (SWIR, MWIR) regions of the electromagnetic spectrum. As elastomers, fully solid CLCEs can be mechanically deformed to tune the selective reflection. This report details approaches to tune selective reflection, including mechanical deformation, incidence angle, thermochromism, and dielectric actuation. Generally, the optomechanical response of the CLCE at longer pitch lengths (e.g., infrared reflecting) is comparatively less than that of prior examinations of analogous compositions with a shorter pitch. Furthermore, the contribution of modulus and dielectric breakdown to electromechanical response is examined. 

The directional deformation of liquid crystalline elastomers (LCEs) is predicated on alignment, enforced by various processing techniques. Specifically, surface-aligned LCEs can exhibit higher temperature thermomechanical responses and weakened strain−temperature coupling in comparison to LCEs subjected to mechanical or rheological alignment. Recently, we reported enhanced stimuli response of mechanically aligned LCEs containing supramolecular liquid crystals. Here, we prepare supramolecular LCEs via surface-enforced alignment to study the impact of the supramolecular bond strength and intermolecular forces. This was evaluated using oxybenzoic acid (OBA) derivatives with and without pendant methyl groups as well as via oxybenzoic acid-pyridine complexes. Increased incorporation of supramolecular mesogens reduces the isotropic transition temperature and generally increases the strain−temperature coupling. The number of elastically active strands per unit volume, hydrogen bond conformations, and network morphology are affected by the supramolecular mesogens and influence the observed stimuli response. Overall, reduced intermolecular interactions correlate with more desirable actuation properties, demonstrating the influence of the supramolecular mesogen’s structure. 

Polyacrylamide tanglemers with photodegradable crosslinkers afford spatiotemporal control over the stability of entanglement-trapping crosslinks, influencing regional swelling and increased extensibilityviachain lengthening. 

Abstract The electrically‐directed, isothermal response of liquid crystal elastomers (LCEs) to an applied electric field is a compelling approach to realize spatially tailorable, sequence‐controllable, and high‐frequency deformation. The electromechanical response is facilitated by coating aligned LCEs with compliant electrodes. Upon application of an electric field, the electrodes attract and generate Maxwell stress. The directional difference in moduli for aligned LCEs produces directional deformation of the material and does not require mechanical bias or framing. Here, LCEs prepared from a newly reported thiol‐ene reaction are explored as DEAs with improved mechanical and dielectric properties. This report details that incorporating a difunctional liquid crystalline monomer composed of allyl ether functional groups reduces Young's modulus, increases the dielectric constant, and improves cyclic recovery compared to an analogous LCE prepared by thiol‐ene polymerization. Electrically‐induced, isothermal deformation of as much as 30% strain is reported. The facile chemistry and enhanced electromechanical response reported here may enable the functional integration of LCEs in applications such as robotics. 

Liquid crystalline elastomers (LCEs) are soft materials which disorder upon heating through the isotropic transition temperature. The order-disorder phase transition of LCEs results in a contraction of up to ∼50% along the aligned axis. Motivated by this distinctive stimuli-response, LCEs are increasingly considered as low-density actuators. Generally, LCEs are composed entirely of covalent bonds. Recently, we have prepared LCEs with intramesogenic supramolecular bonds from dimerized oxybenzoic acid derivatives and documented distinctive thermomechanical response in these supramolecular LCEs. Here, we report a detailed investigation of phase transitions in supramolecular LCEs by systematically varying the composition to affect the strength of the intermolecular interactions in the polymer network. The order-disorder phase transition is shown to be influenced by the conformation and dissociation of supramolecular dimers. Distinctly, this report isolates and details an LCE composition which undergoes an intermediate transition to an incommensurate phase at lower temperatures than the order-disorder transition. 

Abstract Hydrogels are often synthesized through photoinitiated step‐, chain‐, and mixed‐mode polymerizations, generating diverse network topologies and resultant material properties that depend on the underlying network connectivity. While many photocrosslinking reactions are available, few afford controllable connectivity of the hydrogel network. Herein, a versatile photochemical strategy is introduced for tuning the structure of poly(ethylene glycol) (PEG) hydrogels using macromolecular monomers functionalized with maleimide and styrene moieties. Hydrogels are prepared along a gradient of topologies by varying the ratio of step‐growth (maleimide dimerization) to chain‐growth (maleimide‐styrene alternating copolymerization) network‐forming reactions. The initial PEG content and final network physical properties (e.g., modulus, swelling, diffusivity) are tailored in an independent manner, highlighting configurable gel mechanics and reactivity. These photochemical reactions allow high‐fidelity photopatterning and 3D printing and are compatible with 2D and 3D cell culture. Ultimately, this photopolymer chemistry allows facile control over network connectivity to achieve adjustable material properties for broad applications.