Soft actuators designed from stimuli-responsive polymers often possess a certain amount of bionic functionality because of their versatile deformation. Liquid-crystalline polymers (LCPs) and their ...composites are among the most fascinating materials for soft actuators due to their great advantages of flexible structure design and easy regulation. In this Spotlight on Applications, we mainly focus on our group’s latest research progress in soft actuators based on LCPs and their composites. Some representative research findings from other groups are also included for a better understanding of this research field. Above all, the essential principles for the responsive behavior and reconfigurable performance of the soft actuators are discussed, from the perspective of material morphology and structure design. Further on, we analyze recent work on how to precisely regulate the responsive modes and quantify the operating parameters of soft actuators. Finally, some application examples are given to demonstrate well-designed soft actuators with different functions under varied working environments, which is expected to provide inspiration for future research in developing more intelligent and multifunctional integrated soft actuators.
Our research provides a potential avenue for preparing high-performance all-organic polymer dielectrics via optimizing sequential structure of polystyrene-based copolymers.
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•All ...organic P(St-co-CBMA) dielectrics with high-performance are synthesized.•Improved permittivity and breakdown strength are achieved in the copolymer.•An outstanding Ue of 8.94 J/cm3 and high η of 87.4% at 476 MV/m are achieved in the designed copolymer.
It is a great challenge to improve simultaneously the permittivity (εr) and breakdown strength of polymer dielectrics. The linear polystyrene (PS) has the advantages of low cost, easy processing and high charge-discharge efficiency (η). However, the low εr and low breakdown strength result in the low discharge energy density (Ue) of PS. For polar liquid crystalline polymer poly11-((4′-cyano-1,1′-biphenyl-4-yl)oxy)undecyl methacrylate (PCBMA), it shows the merit of high εr, low band gap width and good film-forming property. In this paper, random copolymers P(St-co-CBMA) and block copolymers PS-b-PCBMA were synthesized by radical polymerization and reversible addition-breaking chain transfer polymerization, respectively. The effect of sequential structure on the dielectric behaviors and energy storage properties of polystyrene copolymers is investigated in detail. The experimental results indicate that a high εr value of 5.2 (±0.049), an outstanding Ue of 8.94 J/cm3 and high η of 87.4% at 476 MV/m are achieved in random copolymer P(St-co-CBMA) with the 92 mol% content of CBMA unit because of the strong orientation polarization, deep traps and good film-forming property. This work demonstrates that it is a feasible strategy to obtain high performance polystyrene copolymer dielectrics via tailoring sequential structure between functional monomer and styrene monomer.
•The mechanism of transesterification catalyzed by zinc(II) carboxylate was proposed.•The energetically favored catalytic pathway was established by DFT calculations.•O atoms in zinc(II) carboxylate ...serve as the bridge to transfer proton.•Zinc pivalate is of the highest catalytic activity among chosen catalysts.•The catalytic efficiency predicted by energy barrier agrees with experiment.
A deep insight into the reaction mechanism is essential to control the polymerization process with the desired macromolecular structure for high-performance thermotropic liquid crystalline polymer. In this work, density functional theory (DFT) was used to investigate the catalytic polymerization mechanism for the synthesis of thermotropic liquid crystalline polymer catalyzed by zinc(II) carboxylate. The polymerization of 4-acetoxybenzoic acid was studied as a typical reaction. Based on DFT calculations, the rate-limiting step is located in the transesterification between phenol and anhydride acid. The energetically favored pathway was found with the free energy barrier of 51.84 kcal/mol in the presence of zinc acetate, which is significantly lower than the energy barrier without a catalyst. In addition, the effects of the carboxylate group of zinc(II) carboxylate on the catalytic efficiency were revealed by DFT calculations and experiments. Compared with zinc acetate, zinc pivalate has a higher catalytic activity with the rate constant of 1.69 × 10-2 min−1∙M−1 fitted with a second-order reaction model. The HOMO-LUMO gap of zinc pivalate was the smallest among the chosen catalyst, indicating that the chemical activity was strengthened by the methyl substituted. Furthermore, due to the enhanced orbital interactions and the decreased distortion energy in the transition state using zinc pivalate, the energy barrier of the rate-limiting step decreased to 51.36 kcal/mol. These results provide valuable guidance for modeling the catalytic mechanism in aromatic polyester systems.
We report a new computational approach to model hard–soft block copolymers like polyurea as a liquid crystalline polymer to understand their microstructural evolution due to mechanical loading. The ...resulting microstructure closely resembles the microstructure of polyurea. The normalized stress–strain relations in uniaxial compression and tension loading obtained from the model are also in qualitative agreement with the experimental data for polyurea. We use the model to elucidate the evolution of the hard and the soft domains during loading, which is consistent with the experimental measurements characterizing microstructural evolution in polyurea.
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•A new generic coarse-grained model of polyurea as a liquid-crystalline polymer is developed.•The resulting microstructure closely resembles the phase-segregated microstructure of polyurea.•Simulated uniaxial stress–strain response is in close agreement with the response of polyurea.•Strain-induced microstructural evolution in simulation conforms to experimental observations.
Shear transparent cellulose free‐standing thin films can develop iridescence similar to that found in petals of the tulip “Queen of the Night.” The iridescence of the film arises from the modulation ...of the surface into bands periodically spread perpendicular to the shear direction. Small amounts of nanocrystalline cellulose (NCC) rods in the precursor liquid‐crystalline solutions do not disturb the optical properties of the solutions but enhance the mechanical characteristics of the films and affects their iridescence. Smaller bands periodicity, not affected by the NCC rods, slightly deviated from the shear direction is also observed. NCCs are crucial to tune and understand the film's surface features formation. Our findings could lead to new materials for application in soft reflective screens and devices.
Shear transparent free‐standing cellulosic films, prepared from liquid‐crystalline solutions, can develop iridescence arising from the modulation of the surface of the films, similar to that found in the petals of the tulip variety “Queen of the Night.”
Liquid crystalline polymer (LCP) is a promising candidate in the design and fabrication of intelligent soft materials due to the combination of programmable anisotropy and elasticity. Here, a novel ...strategy to fabricate reprogrammable humidity-responsive LCP materials enabled by dynamic ionic cross-links were put forward. The prepared LCP film deforms reversibly with the change of relative humidity (RH). However, the humidity responsivity loses after soaking the film into CaCl2 solution because of the lock of hygroscopic groups by the formed ionic bonds. By selectively cross-linking specific regions of the LCP film, distinctive humidity-driven motions of the film could be realized. More interestingly, by the EDTA-2K solution treatment, ionic cross-links can be interrupted, leading the LCP film responsive to humidity again. Thanks to feasibly removable ionic cross-links, the humidity-directed soft actuator was totally reprogrammable. The behavior of the novel actuator could be manipulated by either the mesogens alignment or the spatially ionic treatment, providing a feasible but robust strategy to fabricate complex humidity-driven soft robots.
Mechanical swing is common in nature, such as sound waves, wingbeat of birds, and heartbeat, which is important to convert input energy into continuous motion. Here, we report a photodriven swing ...actuator composed of commercially available polyimide (Kapton) and azobenzene-containing liquid-crystalline polymers. The liquid-crystalline polymers act as the photoactive layer, which were synthesized by copolymerization of one benzenecarboxylic acid-containing monomer (M6BCOOH) and one azobenzene-containing monomer (M6ABOC2) with different molar ratios. The Kapton layer with a high elastic modulus is photoinert and functions as the substrate layer. After thermal annealing, the film displays chaotic swing under continuous irradiation of actinic light. Interestingly, the swing amplitude is greatly enhanced by the existence of supramolecular hydrogen bonding in liquid-crystalline polymer films. It is the introduction of M6BCOOH to the copolymer that accelerates the trans–cis photoisomerization rate of azobenzenes. Also, it forms a hydrogen bond as physical crosslinking sites, enabling the polymer film to work as a whole. Thus, it enhances the driving force for photomechanical deformation. Moreover, it improves the elastic modulus of the photoactive layer and modulates the swing behavior of the bilayer strip. More importantly, the formation of a hydrogen bond in the form of acidic dimers has a spatial confinement effect, extending the timescale of photodriven swing. The photomechanical self-vibration of the bilayer film can be ascribed to the combination of the photoisomerization process of azobenzenes with the local photosoftening effect of liquid-crystalline polymers.
The effect of mechanical recycling on the properties of injection-molded polypropylene (PP) reinforced with thermotropic liquid crystalline polymer (TLCP) or long glass fiber (GF) has been ...investigated. The 30 and 50 wt% in situ TCLP and GF reinforced composites were mechanically recycled for three processing cycles, using an injection molding machine with an end-gated plaque mold. The processing temperatures used in the mechanical recycling were determined using rheological and thermogravimetric analyses to minimize the degradation of polypropylene. Recycled TLCP/PP maintained its mechanical properties, and recycling had no significant influence on its morphological, thermal, rheological, and thermo-mechanical properties. Morphological investigation illustrated the regeneration of TLCP fibrils during the mold filling process of each recycle. By the addition of maleic anhydride-grafted polypropylene (MAPP), significant improvements in the mechanical properties of TLCP/PP without impact on recyclability were observed. In contrast, the tensile strength of 50 wt% glass fiber reinforced composite decreased 30% while the tensile modulus decreased 5% after the third recycle. Glass fiber filled polypropylene exhibited significant fiber shortening and was not able to regenerate fibers in processing. Fiber length attrition during the recycling process led to the deterioration of the mechanical properties of the recycled glass filled composites.
By connecting a fluorinated molecule 2,5-bis((4-(perfluorohexyl)benzoyl)oxy)benzoic acid (6DFP) to the poly(4-vinylpyridine) (P4VP) backbone through hydrogen bonding, we synthesized a new series of ...fluorinated supramolecular mesogen-jacketed liquid crystalline polymer (MJLCP) P4VP(6DFP)x, where x is the molar ratio of donor to acceptor. Polarized light microscopy and wide-angle X-ray scattering were used to investigate the liquid crystallinity of the resulting complexes. The results show that this kind of supramolecular MJLCP has good thermal stability, with the isotropization temperature of about 170 °C. Subsequently, by connecting the fluorinated molecule 6DFP to the commercially available coil−coil block copolymer (BCP) polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) chain also via hydrogen bond, we constructed a series of supramolecular rod−coil BCP PSmVn(6DFP)x, where m and n are the degrees of polymerization of PS and P4VP, respectively. PSmVn(6DFP)x exhibits a hierarchically ordered self-assembled structure. Owing to the introduction of fluorine atoms, the Flory-Huggins interaction parameter (χ) of such a supramolecular BCP is high. BCP sample with a low total degree of polymerization can still be ordered, and the periodic size can be as low as 11.5 nm. This work provides a new approach for the construction of small-sized structures by supramolecular BCPs via hydrogen bonding, which can be used as nanotemplates and nanoporous materials after selective removal of the small molecules.
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•Fluorinated supramolecular MJLCP with high stability obtained by hydrogen bonding from a fluorinated small molecule and P4VP.•Fluorinated supramolecular high-χ rod−coil BCP with the above rod-like MJLCP constructed from PS-b-P4VP by hydrogen bonding.•Self-assembled structure of the supramolecular BCP regulated, with a minimum periodic size of 11.5 nm.
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