Crystalline Polymer Networks Research Articles

Stiffness anisotropy coordinates supracellular contractility driving long-range myotube-ECM alignment.

The ability of cells to organize into tissues with proper structure and function requires the effective coordination of proliferation, migration, polarization, and differentiation across length scales. Skeletal muscle is innately anisotropic; however, few biomaterials can emulate mechanical anisotropy to determine its influence on tissue patterning without introducing confounding topography. Here, we demonstrate that substrate stiffness anisotropy coordinates contractility-driven collective cellular dynamics resulting in C2C12 myotube alignment over millimeter-scale distances. When cultured on mechanically anisotropic liquid crystalline polymer networks (LCNs) lacking topography, C2C12 myoblasts collectively polarize in the stiffest direction. Cellular coordination is amplified through reciprocal cell-ECM dynamics that emerge during fusion, driving global myotube-ECM ordering. Conversely, myotube alignment was restricted to small local domains with no directional preference on mechanically isotropic LCNs of the same chemical formulation. These findings provide valuable insights for designing biomaterials that mimic anisotropic microenvironments and underscore the importance of stiffness anisotropy in orchestrating tissue morphogenesis.

Color-tunable circularly polarized luminescence from liquid crystalline polymer networks

Chiroptical materials with circularly polarized luminescence (CPL) activities have attracted increasing interest because of their promising applications in optoelectronics, biosensing and imaging. Nevertheless, the construction of CPL-active materials with large luminescence dissymmetry (glum) factors and high emission efficiency is still challenging. Herein, a series of liquid crystalline polymer network films have been prepared by photopolymerization of cholesteric liquid-crystalline mixtures doped with aggregation-induced emission-active luminogens, TPE-TA and BDABFN. Through adjustment of the mass ratio of the two luminogens, the resultant films exhibit multicolour CPL from blue to red to white with absolute glum values up to 0.71 and fluorescence quantum yields up to 44 %. This work provides a strategy for fabricating polymeric film materials with color-tunable CPL properties and high fluorescence efficiency.

Efficient multicolour and white circularly polarized luminescence from liquid crystalline polymer networks.

Twelve liquid crystalline polymer network films were fabricated through photopolymerization of cholesteric liquid-crystalline mixtures containing two aggregation-induced emissive-active luminogens. The films exhibit multicolour and white circularly polarized luminescence with dissymmetry factors up to 0.85 and fluorescence quantum yields up to 90%.

Formation of tannic acid-calcium polymeric network in pore solution: Characterization and kinetics

This study investigates the changes of tannic acid (TA) at varying concentrations in cement pore solution. Interestingly, TA spontaneously forms nanosheet tannic acid-calcium polymeric networks (TA-Ca) by interacting with Ca2+. Spectral, thermal, ionic and organic carbon analyses determine the composition and structural characteristics of these networks and detail the formation mechanism. The networks are connected via hydrogen bonding, C–C coupling and complexation. Moreover, network composition, structure and formation are closely dependent on TA concentration. At low concentrations, crystalline coordination polymer networks form, following second-order kinetics (key factor: Ca2+ concentration). At high concentrations, amorphous C–C coupled polymer networks form, following first-order kinetics (key factor: catalytic oxidation of Ca2+). This study aims to elucidate the reaction and mechanism of TA in cement paste, providing a novel theoretical basis for applying renewable bio-admixtures in sustainable construction.

Solutions Are the Problem: Ordered Two-Dimensional Covalent Organic Framework Films by Chemical Vapor Deposition.

Covalent organic frameworks (COFs) are a promising class of crystalline polymer networks that are useful due to their high porosity, versatile functionality, and tunable architecture. Conventional solution-based methods of producing COFs are marred by slow reactions that produce powders that are difficult to process into adaptable form factors for functional applications, and there is a need for facile and fast synthesis techniques for making crystalline and ordered covalent organic framework (COF) thin films. In this work, we report a chemical vapor deposition (CVD) approach utilizing co-evaporation of two monomers onto a heated substrate to produce highly crystalline, defect-free COF films and coatings with hydrazone, imine, and ketoenamine COF linkages. This all-in-one synthesis technique produces highly crystalline, 40 nm-1 μm-thick COF films on Si/SiO2 substrates in less than 30 min. Crystallinity and alignment were proven by using a combination of grazing-incidence wide-angle X-ray scattering (GIWAXS) and transmission electron microscopy (TEM), and successful conversion of the monomers to produce the target COF was supported by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and UV-vis measurements. Additionally, we used atomic force microscopy (AFM) to investigate the growth mechanisms of these films, showing the coalescence of triangular crystallites into a smooth film. To show the wide applicability and scope of the CVD process, we also prepared crystalline ordered COF films with imine and ketoenamine linkages. These films show potential as high-quality size exclusion membranes, catalytic platforms, and organic transistors.

Accelerated ion transportation in liquid crystalline polymer networks for superior solid-state lithium metal batteries

The application of solid polymer electrolyte in high energy density lithium metal batteries is limited by low Li+ mobility, low ionic conductivity and poor cycle stability at room temperature. In the study, the free-standing flexible polymeric electrolytes (PCREs) with semi-interpenetrating-network in the topological nanostructures were fabricated through the in-situ UV-photopolymerization of the liquid crystalline monomers and poly(ethylene glycol) diglycidyl ether. Remarkably, by optimizing the relative proportion of the two liquid crystalline monomers with different methylene chains as connected bridge band between rigid center and terminal acrylate functional groups, the electrochemical properties of the prepared PCREs were successfully improved, which might contributed to the suitable ion transport channels in the porous polymer network structures. The prepared PCRE exhibited increased ion migration number, excellent ionic conductivity and a wide electrochemical window. Through the calculation of density functional theory and molecular dynamics simulation, the difference in the molecular orbital of liquid crystalline polymers and the mechanism of PCREs enhancement tLi+ were well understood. The study may provide new perspectives for the design and fabrication of high-performance polymer electrolyte materials, which will promote the development and practical application of the all-solid lithium metal batteries.

A Photomechanical Film in which Liquid Crystal Design Shifts the Absorption into the Visible Light Range.

Liquid crystalline polymer networks (LCN) with azobenzene monomers bend reversibly under UV-light irradiation, combining photomechanical and photothermal effects. However, the harmful nature of UV-light limits their use in biology and soft robotics. Although visible light-absorbing tetra-ortho-fluoro-substituted azobenzenes exist, liquid crystalline monomers have never been prepared. Previously, such azobenzenes were added as photoactive additives (up to 10%) to otherwise passive liquid crystalline polymer networks. In this work, a molecular design of a liquid crystalline, polymerizable azobenzene switchable by visible light is presented. The monomer assembles in a highly fluid nematic phase, but polymerizes in a layered smectic C phase. The films are produced solely from the monomer without additional liquid crystalline components and are actuated with visible light. Bending experiments in air and under water differentiate photomechanical and photothermal effects. Remarkably, a 60µm splay aligned film maintains its deformation for hours, slowly reverting over days. Monomer liquid crystallinity is characterized using differential scanning calorimetry (DSC), wide-angle X-ray scattering (WAXS), and polarized optical microscopy (POM); polymer films are analyzed using WAXS and DSC on a homogeneously aligned film. The synthetic procedure is high yielding and polymer film fabrication is scalable, which enables the use of safe and efficient photomechanical LCNs in soft robotics, engineering and biology.

Binary Double Network-like Structure: An Effective Energy-Dissipation System for Strong Tough Hydrogel Design.

Currently, hydrogels simultaneously featuring high strength, high toughness, superior recoverability, and benign anti-fatigue properties have demonstrated great application potential in broad fields; thus, great efforts have been made by researchers to develop satisfactory hydrogels. Inspired by the double network (DN)-like theory, we previously reported a novel high-strength/high-toughness hydrogel which had two consecutive energy-dissipation systems, namely, the unzipping of coordinate bonds and the dissociation of the crystalline network. However, this structural design greatly damaged its stretchability, toughness recoverability, shape recoverability, and anti-fatigue capability. Thus, we realized that a soft/ductile matrix is indispensable for an advanced strong tough hydrogel. On basis of our previous work, we herein reported a modified energy-dissipation model, namely, a "binary DN-like structure" for strong tough hydrogel design for the first time. This structural model comprises three interpenetrated polymer networks: a covalent/ionic dually crosslinked tightened polymer network (stiff, first order network), a constrictive crystalline polymer network (sub-stiff, second order network), and a ductile/flexible polymer network (soft, third order network). We hypothesized that under low tension, the first order network served as the sacrificing phase through decoordination of ionic crosslinks, while the second order and third order networks together functioned as the elastic matrix phase; under high tension, the second order network worked as the energy dissipation phase (ionic crosslinks have been destroyed at the time), while the third order network played the role of the elastic matrix phase. Owing to the "binary DN-like" structure, the as-prepared hydrogel, in principle, should demonstrate enhanced energy dissipation capability, toughness/shape recoverability, and anti-fatigue/anti-tearing capability. Finally, through a series of characterizations, the unique "binary DN-like" structure was proved to fit well with our initial theoretical assumption. Moreover, compared to other energy-dissipation models, this structural design showed a significant advantage regarding comprehensive properties. Therefore, we think this design philosophy would inspire the development of advanced strong tough hydrogel in the future.

Circularly polarized organic room temperature phosphorescence activated by liquid crystalline polymer networks

Circularly polarized organic room temperature phosphorescence (CPRTP) withgmax= +0.098 was activated by the rigid environment of anin situcross-linked liquid crystalline polymer network.

Light-triggered autonomous shape-reconfigurable and locomotive rechargeable power sources

Soft electronics have garnered considerable attention as a promising alternative to conventional electronics with fixed shapes and sizes because of their facile and intimate shape-adaptability to complex operating environments. Their practical applications, however, have been plagued by limited maneuverability, which predominantly stemmed from tethered electrical cords or rigid/bulky power sources. Here, we present light-triggered autonomous shape-reconfigurable and locomotive rechargeable power sources (SL-PSs), in which quasi-solid-state supercapacitors (SCs) are monolithically integrated with thermoresponsive liquid crystalline polymer networks (LCNs) substrates using a device-customized printing process. The SCs are designed to enable photothermal effect as well as adjustable capacitive storage. The LCNs are synthesized to provide thermomechanical deformation by programmable anisotropic molecular contract/expansion. Upon exposure to light or heat, the SL-PSs exhibit autonomous and reversible shape-morphing within a few seconds without impairing their electrochemical performance. Moreover, the SL-PSs convey a model cargo through photothermal stimuli-induced wire-crawling and simultaneously transfer their on-board stored electrical energy, demonstrating their potential viability as an untethered soft robotic power source.

Inside Back Cover: Mechanochromic, Shape‐Programmable and Self‐Healable Cholesteric Liquid Crystal Elastomers Enabled by Dynamic Covalent Boronic Ester Bonds (Angew. Chem. Int. Ed. 9/2022)

Reprogrammable elastomers with dynamic covalent bonds are of paramount significance for emerging applications such as adaptive optics and soft robotics. In their Research Article (e202116219), Ling Wang, Wei Feng, and co-workers describe mechanochromic, shape-programmable, and self-healable cholesteric liquid crystal elastomers obtained by introducing dynamic covalent boronic ester bonds into the main-chain chiral liquid crystalline polymer networks.

Electro-optic characteristics of stabilized cholesteric liquid crystals with non-liquid crystalline polymer networks

Extensive prior research has explored the stabilization of the CLC phase with polymer networks. These prior efforts have demonstrated both tunable and switchable electro-optic reconfiguration of the selective reflection of the CLC phase. Recently, we and other groups have detailed that polymer stabilization of the CLC phase with liquid crystalline monomers retains "structural" chirality (e.g., the chiral phase templates the morphology of the achiral polymer network). Here, we demonstrate that structural chirality can be retained in aliphatic, non-liquid crystalline monomers. PSCLCs prepared by photoinitiated polymerization of aliphatic polymer networks exhibit reversible electro-optic responses. Facilitated by the retention of structural chirality in aliphatic stabilizing polymer networks, we explore the role of surface affinity and crosslink density in the transfer of structural chirality to the liquid crystal media.

Photo-Responsivity Improvement of Photo-Mobile Polymers Actuators Based on a Novel LCs/Azobenzene Copolymer and ZnO Nanoparticles Network.

The efficiency of photomobile polymers (PMP) in the conversion of light into mechanical work plays a fundamental role in achieving cutting-edge innovation in the development of novel applications ranging from energy harvesting to sensor approaches. Because of their photochromic properties, azobenzene monomers have been shown to be an efficient material for the preparation of PMPs with appropriate photoresponsivity. Upon integration of the azobenzene molecules as moieties into a polymer, they act as an engine, allowing fast movements of up to 50 Hz. In this work we show a promising approach for integrating ZnO nanoparticles into a liquid crystalline polymer network. The addition of such nanoparticles allows the trapping of incoming light, which acts as diffusive points in the polymer matrix. We characterized the achieved nanocomposite material in terms of thermomechanical and optical properties and finally demonstrated that the doped PMP was better performing that the undoped PMP film.

Light‐Fueled Climbing of Monolithic Torsional Soft Robots via Molecular Engineering

Azobenzene‐functionalized liquid crystalline polymer networks (azo‐LCNs) are promising candidates for light‐fueled contactless manipulation of miniaturized soft robots through embedding photoactive molecular switches into alignment‐programmable LCNs. In particular, the 3D helical geometry of azo‐LCNs is reported to achieve rapid photomotility by introducing rolling resistance. However, the maximum height of the obstacle that soft robot can overcome is limited by the helix diameter and the stress–strain responsivity. Herein, the helical diameter per unit length and photogenerated stress through molecular engineering of photoactive molecular switches are maximized. The carbon number of aliphatic spacers in the photoactive molecular switches is varied from two to eight to systematically investigate the structure–property–performance relations by studying the molecular geometry, physical properties of polymers, and photomotility of polymers. Furthermore, a finite‐element analysis simulation is presented to understand the rolling locomotion of helical torsional soft robots. Through molecular engineering, the helix diameter per unit length of 0.2 mg soft robots is maximized, demonstrating high Young's modulus (≈2 GPa) and photogenerated stress (>1 MPa), as well as large velocity per body length, compared with the previously reported soft robots. Finally, the molecularly engineered soft robots successfully climb stairs, which is a key task in robotic systems.

Photo‐Triggered Shape Reconfiguration in Stretchable Reduced Graphene Oxide‐Patterned Azobenzene‐Functionalized Liquid Crystalline Polymer Networks

AbstractIn recent years, the “Kirigami” have been exploited to engineer stretchable electronics that exhibit enhanced deformability without sacrificing their mechanical and electrical properties. However, kirigami‐inspired engineering is often limited to passive mechanical stretching for 3D shape morphing. To counter this problem, in this study, azobenzene‐functionalized liquid crystalline polymer networks (azo‐LCNs) are monolithically integrated with patterned reduced graphene oxide (rGO), called azo‐LCN/rGO, to achieve on‐demand shape reconfiguration in response to external stimuli (UV, NIR, solar rays, and portable light); in addition, the azo‐LCN/rGO exhibit highly enhanced mechanical and electrical properties. The cross‐sectional area and thickness of rGO patterns are controlled using a masking technique and evaporative self‐assembly. By the spatial patterning of rGO, insulating azo‐LCNs are converted into electrically conducting structures (381.9 S cm−1). The elastic modulus of <2 µm thick azo‐LCN can be tailored in the range of 1.3–6.4 GPa by integration with rGO layers of thickness less than 2 µm. Upon UV irradiation, azo‐LCN/rGO exhibit both for/backward in‐plane bending as well as out‐of‐plane chiral twisting, thus overcoming the typical trade‐off relationship between elastic modulus and deformability. Finally, an on‐demand contactless shape reconfiguration in azo‐LCN/rGO by UV irradiation in conjunction with passive mechanical strain is demonstrated.

Smectic Liquid Crystalline Polymer Membranes with Aligned Nanopores in an Anisotropic Scaffold.

Bottom-up methods for the fabrication of nanoporous polymer membranes have numerous advantages. However, it remains challenging to fabricate nanoporous membranes that are mechanically robust and have aligned pores, that is, with a low tortuosity. Here, a mechanically robust thin-film composite membrane was fabricated consisting of a two-dimensional (2D) porous smectic liquid crystalline polymer network inside an anisotropic, microporous polymer scaffold. The polymer scaffold allows for relatively straightforward planar alignment of the smectic liquid crystalline mixture, which consisted of a diacrylate cross-linker and a dimer forming benzoic acid-based monoacrylate. Polymerized samples displayed a smectic A (SmA) phase, which formed the eventual 2D porous channels after base treatment. The aligned 2D nanoporous membranes showed a high rejection of anionic solutes bigger than 322 g/mol. Cleaning and reusability of the system were demonstrated by intentionally fouling the porous channels with a cationic dye and subsequently cleaning the membrane with an acidic solution. After cleaning, the membrane properties were unaffected; this, combined with numerous pressurizing cycles, demonstrated reusability of the system.

Controlled Dynamics of Neural Tumor Cells by Templated Liquid Crystalline Polymer Networks.

The ability to control the alignment and organization of cell populations has great potential for tissue engineering and regenerative medicine. A variety of approaches such as nano/microtopographical patterning, mechanical loading, and nanocomposite synthesis have been developed to engineer scaffolds able to control cellular properties and behaviors. In this work, a patterned liquid crystal polymer network (LCN) film is synthesized by using a nematic liquid crystal template in which the molecular orientations are predesigned by photopatterning technique. Various configurations of polymer networks such as linear and circular patterns are created. When neural tumor cells are plated onto the templated LCN films, the cell alignment, migration, and proliferation are directed in both linear and curvilinear fashions following the pattern of the aligned polymer chains. A complex LCN pattern with zigzag geometry is also fabricated and found to be capable of controlling cell alignment and collective cellular organization. The demonstrated control of cell dynamics and organization by LCN films with various molecular alignments opens new opportunities to design scaffolds to control cultured cell organization in a manner resembling that found in tissues and to develop novel advanced materials for nerve repair, tissue engineering, and regenerative medicine applications.

Preparation of liquid crystalline polymer networks containing a cinnamyl group in the main chain with tunable thermal actuation behavior

ABSTRACTA series of liquid crystalline copolyesters (LCPs) with different concentrations of a photocrosslinking moiety have been synthesized by random polycondensation with 4,4′‐bis(6‐hydroxyhexyloxy)biphenyl, 2‐phenylsuccinic acid, and 4‐(6‐hydroxyhexyloxy)cinnamic acid (6HCA). Multifunctional monodomain liquid crystal networks (LCNs) with considerable and tunable actuation behavior are obtained by postphotocrosslinking. The influence of the photocrosslinking moiety on the phase transition behavior of the LCP and actuation behavior of the LCN has been investigated. The results suggest that incorporating 6HCA suppresses the smectic phase of the LCP and decreases the nematic‐isotropic phase transition temperature. Moreover, the starting actuation temperature of the LCN decreases from 55 to 40 °C as the 6HCA reached 50%. In addition, the actuation force and storage modulus of the LCN actuators are enhanced by incorporating a high concentration of 6HCA. A 1.64 MPa contractile force can be achieved, and it can lift burdens 1300 times heavier than its weight when 50% 6HCA is incorporated into the LCP. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2019, 57, 904–911

Cationic photopolymerization of liquid crystalline epoxide in mesogenic solvents and its application in polymer-stabilized liquid crystals

A novel approach to fabricate epoxy-based polymer-stabilized liquid crystals (EPSLCs) via the cationic photopolymerization of liquid crystalline epoxide in mesogenic solvents was presented. The photoinitiated cationic polymerization of liquid crystalline epoxide in different mesogenic solvents was compared and the liquid crystalline epoxy polymer (LCEP) network can only be formed in the particular solvents. The different photo-curing behaviors of the liquid crystalline epoxide in various solvents may be ascribed to the solvent effect and the content of the nucleophilic groups had a decisive influence on the formation of the LCEP network. The epoxy polymer/liquid crystal (LC) composites were also prepared by the cationic photopolymerization of different epoxy monomers in LC solvent. The morphology of the epoxy polymers in the composites and the change of the arrangement of LC molecules before and after polymerization were also studied. Moreover, the stabilizing effect of the LCEP network on the LC molecules was also characterized by the electric-optical performance test. This report can offer an innovative technique to fabricate EPSLCs and provide a promising means for the development of functional epoxy polymer composites.

A facile route towards controllable electric-optical performance of polymer-dispersed liquid crystal via the implantation of liquid crystalline epoxy network in conventional resin

A liquid crystalline epoxide was synthesized and its curing reactivity was compared with that of the conventional epoxy monomers. By utilizing the difference in curing reactivity between the liquid crystalline epoxide and non-liquid crystalline epoxy monomers, a coexistent system of polymer-dispersed and polymer-stabilized liquid crystal (LC) in the intelligent films can be obtained by two-step thermal curing method. If the later curing process was undertaken under an external electric field, the ordered microstructure of liquid crystalline epoxy polymer (LCEP) network can be implanted into the conventional epoxy resin. The competition of the anchoring effect on the LC molecules from the LCEP network and the conventional epoxy resin matrix was crucial to the electro-optical performance of the films. Moreover, the performance of the films can be adjusted by controlling the content of liquid crystalline epoxide and the external electric field applied during later curing. This approach can provide a facile route to regulate the electric-optical performance of polymer-dispersed liquid crystal films for practical applications.