LC Monomer Research Articles

Fabricating Freestanding, Broadband Reflective Cholesteric Liquid-Crystal Networks via Topological Tailoring of the Sm-Ch Phase Transition.

Numerous biological systems in nature provide much inspiration for humanity to master diverse coloration strategies for creating stimuli-responsive materials and display devices, such as to access gorgeous structural colors from well-defined photonic structures. Cholesteric liquid crystals (CLCs) are a fascinating genre of photonic materials displaying iridescent colors responsive to circumstance changes; however, it is still a big challenge to design materials with broadband color variation as well as good flexibility and freestanding capacity. Herein, we report a feasible and flexible strategy to fabricate cholesteric liquid-crystal networks (CLCNs) with precise colors across the entire visible spectrum through molecular structure tailoring and topology engineering and demonstrate their application as smart displays and rewritable photonic paper. Influences of chiral and achiral LC monomers on the thermochromic behaviors of CLC precursors as well as on the topology of the polymerized CLCNs are systematically investigated, demonstrating that the monoacrylate achiral LC facilitated the formation of a smectic phase-chiral phase (Sm-Ch) pretransitional phase in the CLC mixture and improved the flexibility of the photopolymerized CLCNs. High-resolution multicolor patterns in one CLCN film are generated through photomask polymerization. In addition, the freestanding CLCN films show perceivable mechanochromic behaviors and repeated erasing-rewriting performances. This work opens avenues toward the realization of pixelated colorful patterns and rewritable CLCN films promising in technology fields ranging from information storage and smart camouflage to anti-counterfeiting and smart display.

Ultrasonic-Excited Ultrafast Seamless Integration of Heterostructured Liquid Crystalline Elastomers for Multi-responsive Soft Actuators.

Multicomponent/heterostructured liquid crystalline elastomers (LCEs) have recently garnered extensive attention for the design of soft robots with high dexterity and flexibility. However, the reported integration strategies of LCEs seriously suffer from high welding temperature, long processing time, and poor joint quality. Herein, the high-efficiency seamless ultrasonic welding (UW) of reprogrammable silver nanowire-LCE composites (AgNW-LCEs) have been realized without any auxiliary reagents based on the dynamic silver-disulfide coordination interactions. The elaborate combination of silver-disulfide coordination interactions and UW technology establishes an effective double-network welding mechanism of AgNWs and dynamic LC networks due to the high-frequency vibration at the welding interface. During the UW process, monolithic AgNW-LCEs can be integrated into heterostructured actuators at room temperature for 0.68 s. Furthermore, the welded AgNW-LCEs demonstrate an exceptional strain healing efficiency of ∼100%, a stress healing efficiency of ∼85%, and a maintained orientation of the LC alignment. Taking advantage of the high-efficiency UW technology, the heterostructured AgNW-LCE actuators with different LC alignments or LC monomers have been successfully implemented for a multi-degree-of-freedom soft robotic arm and a time-modulated flower-mimic actuator. This work provides an efficient approach toward the development of multi-responsive entirely soft actuators based on smart polymers.

Multifunctional Liquid Crystal Polymer Networks: Azobenzene-Based Monoacrylate Molecules Impart a Photothermal Effect to Polymer Networks

Stimuli-responsive liquid crystal polymer networks (LCPNs) consisting of azobenzene are mostly studied based on ultraviolet (UV)-induced photochemical isomerization. However, depending on the molecular structure and the degree of UV absorption of azobenzene molecules, the photothermal effect can induce stimuli-responsiveness of azobenzene-based LCPN. In this report, an azobenzene-based monoacrylate (AM) monomer that can be easily introduced into an LCPN is designed and synthesized to develop a multifunctional LCPN that exhibits a photothermal effect. An AM LCPN is successfully fabricated with AM, LC monomer, and thiol groups, and the fabricating process is systematically optimized by controlling the ratio of each component. The thermal, mechanical, and structural behaviors of the AM LCPN are confirmed through various experimental analyses, and the shape memory properties are quantitatively and qualitatively verified via dynamic mechanical analysis and photographs. Thanks to the azobenzene molecules present, the AM LCPN exhibits a photothermal effect under UV exposure, which is demonstrated by macroscopic and spectroscopic experiments. Alignment and self-healing experiments indicate that the AM LCPN can be applied to fields requiring orientation or self-healing property.

Photoresponsive α-cyanostilbene-containing fluorescent liquid crystal polymers based on ring-opening metathesis polymerization for information storage and encryption

Photoresponsive polymer materials have attracted great interest because of their prospective applications in sensors, actuators, and smart devices. Here, a photoresponsive fluorescent liquid crystal polymer (LCP) was constructed by the copolymerization of one LC monomer (CH) and another fluorescent monomer containing α-cyanostilbene units (TP) through the ring-opening metathesis polymerization, designated as PCHTP. PCHTP has excellent mechanical properties and can be processed by simple chemical solvents or melting. The ordered arrangement of LC molecules in the PCHTP film is controlled by the photoinduced alignment technique, resulting in a highly polarized emission pattern at the macroscopic scale. In addition, the luminescence intensity of the PCHTP fibers and films can be tuned upon visible and UV light irradiations by exploiting Z/E photoisomerization of α-cyanostilbene units. Finally, the dual-mode emission pattern with polarization luminescence and tunable photoluminescence was presented in the PCHTP film for information storage and encoding applications. This strategy provides a versatile platform for information storage and encoding using the photoresponsive fluorescent LCPs.

Light-Powered Self-Sustained Oscillators of Graphene Oxide/Liquid Crystalline Network Composites Showing Amplitude and Frequency Superposition.

Light-activated self-oscillators have drawn enormous attention for their potential applications in mobile machines, energy harvesting, signal modulation, etc. Herein, we report one graphene oxide (GO)/liquid crystalline network (LCN) actuator that presents a unique light-activated oscillation with amplitude and frequency superposition. The GO/LCN composite film is prepared by the one-step polymerization of LC monomers, which favors a splay orientation in LC cells made by gluing together two glass sheets, one coated with photothermal agent GO and the other coated with a rubbed polyimide alignment layer. Owing to the asymmetric contraction/expansion, changing the cutting direction gives rise to notably different actuation behaviors for GO/LCN composite films. Moreover, it twists a little during the deflection process as a result of experimental error during the cutting process, which may cause the strip to be cut inaccurately. When the composite film is embedded in a self-shadowing system, it produces an unconventional hybrid oscillation mode upon near-infrared light irradiation, i.e., bending and twisting oscillation coupled. Furthermore, when the aspect ratio of the film decreases, the twisting mode is suppressed and the actuator changes from a coupled mode to a single bending mode. The proposed strategy may extend the application of GO/LCN composite materials and enrich light-activated self-oscillating behaviors.

4D Printing of Hygroscopic Liquid Crystal Elastomer Actuators.

Liquid crystal elastomers (LCEs) are broadly recognized as programmable actuating materials that are responsive to external stimuli, typically heat or light. Yet, soft LCEs that respond to changes in environmental humidity are not reported, except a few examples based on rigid liquid crystal networks with limited processing. Herein, a new class of highly deformable hygroscopic LCE actuators that can be prepared by versatile processing methods, including surface alignment as well as 3D printing is presented. The dimethylamino-functionalized LCE is prepared by the aza-Michael addition reaction between a reactive LC monomer and N,N'-dimethylethylenediamine as a chain extender, followed by photopolymerization. The humidity-responsive properties are introduced by activating one of the LCE surfaces with an acidic solution, which generates cations on the surface and provides asymmetric hydrophilicity to the LCE. The resulting humidity-responsive LCE undergoes programmed and reversible hygroscopic actuation, and its shape transformation can be directed by the cut angle with respect to a nematic director or by localizing activation regions in the LCE. Most importantly, various hygroscopic LCE actuators, including (porous) bilayers, a flower, a concentric square array, and a soft gripper, are successfully fabricated by using LC inks in UV-assisted direct-ink-writing-based 3D printing.

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Large-Size Honeycomb-Shaped and Iris-Like Liquid Crystal Elastomer Actuators

Effect of Isomeric Amine Chain Extenders and Crosslink Density on the Properties of Liquid Crystal Elastomers.

Among the various types of shape changing materials, liquid crystal elastomers (LCEs) have received significant attention as they can undergo programmed and reversible shape transformations. The molecular engineering of LCEs is the key to manipulating their phase transition, mechanical properties, and actuation performance. In this work, LCEs containing three different types of butyl groups (n-, iso-, and sec-butyl) in the side chain were synthesized, and the effect of isomeric amine chain extenders on the thermal, mechanical, and actuation properties of the resulting LCEs was investigated. Because of the considerably low reactivity of the sec-butyl group toward the diacrylate in the LC monomer, only a densely crosslinked LCE was synthesized. Most interestingly, the mechanical properties, actuation temperature, and blocking stress of the LCEs comprising isobutyl groups were higher than those of the LCEs comprising n-butyl groups. This difference was attributed to the presence of branches in the LCEs with isobutyl groups, which resulted in a tighter molecular packing and reduced the free volume. Our results suggest a facile and effective method for synthesizing LCEs with tailored mechanical and actuation properties by the choice of chain extenders, which may advance the development of soft actuators for a variety of applications in aerospace, medicine, and optics.

High-quality tuning of cholesteric liquid crystal lasers based on polymer composite system

Electrically fine tuning is demonstrated in a cholesteric liquid crystal (ChLC) laser based on the polymer composite system. Photo-polymerization in the mixture of LC monomer and LC hardly causes phase separation due to miscibility, forming a microscopically well-mixed polymer-LC composite structure like gel. Light scattering in the polymer-LC composite system decreases with increasing the polymer component, and the composite of equal parts of the polymer and LC exhibits high transparency in electric modulation of the selective reflection band, resulting in high-quality tuning of lasing wavelength in ChLC laser. In tuning operation, the ChLC laser retains a high slope efficiency greater than 19%, a low threshold smaller than 3 nJ/pulse, and a spectral linewidth narrower than 0.13 nm, while the change in lasing wavelength is fully continuous and reaches 13 nm.

The Characterization and Application of Two Liquid Crystal Mixtures in the Low THz Region

In the previous work, two new nematic liquid crystal (NLC) mixtures, E7-2 and S200-2, were produced by adding eight LC monomers to two commercial LCs S200 and E7, respectively. At λ = 589 nm, the birefringence (Δn) characteristics of the two LC nematic mixtures E7-2 (Δn = 0.260) and S200-2 (Δn = 0.298) are greater than those of the commercial LC E7 (Δn = 0.224) and S200 (Δn = 0.266). The properties (TN-I, ε//, Δɛ, K11, and K33) of these four NLCs were measured. A double-layer metal loop arrays modulation structure based on metamaterial (MM) metal–dielectric–metal (MDM) was designed and fabricated for use in the THz frequency range. The results show that the LC mixtures E7-2 and S200-2 have greater modulation depth (MD) and less modulation insertion loss (IL) than E7 and S200 at THz frequencies. The results show that LC mixtures have significant potential for designing active tunable LC-based devices in the THz and visible light range.

Effect of surface functionalization on the structural properties of single dendrimers: Monte Carlo simulation study

In this study, Monte Carlo simulation results on the structural properties of single dendrimers have been reported. Several dendrimers of varying generation number (GnD3) and core functionality (G3Df), where n = 3–6 and f = 3–6 were considered. The surfaces of each dendrimers are prepared in two ways; one grafted by liquid crystal monomers therein creating liquid crystal dendrimers and the other with similar monomers as the core ones. Then, the effect of surface grafting on the size of the dendrimer, the distribution of monomers, packing fraction and center-to-end distances of terminal groups are investigated. Simulation is performed at several different temperature values to see its effect on those properties. Widely known and easily manageable coarse grained force fields to model monomer-monomer interaction potentials have been used. According to our simulated result, the sizes of dendrimers have been affected by both surface grafting and temperature values. The same generation number and core functionality dendrimers grafted with LC monomers are larger than those without grafting. Similarly, monomer distribution, packing fraction and center-to-end distances have also been sufficiently affected by those parameters.

Floating liquid crystalline molecularly imprinted polymer coated carbon nanotubes for levofloxacin delivery

Liquid crystalline molecularly imprinted polymers (LC-MIPs) were low cross-linking MIPs (5–20 mol%) by introducing a LC monomer into the MIP polymerization system to keep the shape of the imprinted cavities due to additional interactions between the mesogenic groups. The multiwalled carbon nanotubes (MWCNTs) coated LC-MIP (MWCNT@LC-MIP) was the first fabricated as a novel floating interaction-controlled DDS. The synthesis was achieved by adding 9-vinylanthracene to obtain the high-density vinyl group functionalized MWCNTs firstly, and then polymerization of LC MIPs was performed on the surface of MWCNTs using a mixture of methacrylic acid, ethylene glycol dimethacrylate, and 4-methyl phenyl dicyclohexyl ethylene (LC monomer) with levofloxacin (LVF) as model template drug. Both template/functional monomer ratio and levels of crosslinker were optimized to obtain the best imprinting factor. Characterizations of polymer were investigated by the transmission electron microscope, nitrogen adsorption, thermogravimetric analysis, Fourier transform infrared spectra and floating behavior studies. The imprinting effect was confirmed by the adsorption isotherms, adsorption kinetics and effect of selectivity. In vitro release studies were examined by the LVF-loaded MWCNT@LC-MIP and the control samples, MWCNT@LC-NIP, MWCNT@MIP, MWCNT@NIP and the bare MWCNT using acetonitrile as the dissolute medium. The release profiles showed an obvious zero-order release of LVF from MWCNT@LC-MIP, which exhibited 3.8 μg/h of the release rate with duration of about 20 h. In vivo pharmacokinetic study displayed the relative bioavailability of the gastro-floating MWCNT@LC-MIP was 578.9%, whereas only 58.0% of MWCNT@MIP and 11.7% of the bared MWCNT. As a conclusion, MWCNT@LC-MIP showed potentials for oral administration by the innovative combination of floating and controlled release properties.

Solvent-responsive floating liquid crystalline-molecularly imprinted polymers for gastroretentive controlled drug release system

Liquid crystalline-molecularly imprinted polymer (LC-MIP) particles were first found to possess the floating behavior on the aqueous medium. Combined with molecular recognition, the LC-MIP was fabricated as a novel class of the controlled-release gastric retentive DDS. The LC-MIP was made using co-polymerization of methacrylic acid, 4-methyl phenyl dicyclohexyl ethylene (LC monomer with vinyl group), and ethylene glycol dimethacrylate with S-amlodipine (S-AML) as model template drug. The optimum condition of the preparation of LC-MIP has been obtained relying on release behaviors of S-AML from the LC-MIP. The surface morphology of LC-MIP and three corresponding control samples, i.e., template-free LC-NIP, LC-free MIP, and LC-free NIP, were studied. Applying the LF model for the binding isotherm, imprinting factors was 2.80 for the LC-MIP with the crosslinking degree of 20.0%, whereas 6.70 for the LC-free MIP with high levels of crosslinker (80.0%). Furthermore, the phase transition behaviors of LC-based particles as well as drug-loaded LC elastomers were measured by a differential scanning calorimeter and the formed hydrogen bonding between S-AML and LC-MIP was demonstrated by FT-IR spectra. In vivo imaging experiment proved that the floating LC-MIP had significantly longer gastric residence time (>60min) than the non-floating MIP reference (<30min). In vivo pharmacokinetic study showed a plateau region between 1.5 and 22h on the plasma concentration from the LC-MIP. In spite of lower imprinting factor, the relative bioavailability of the gastro-floating LC-MIP was 180.5%, whereas only 111.7% of the LC-free MIP. As a conclusion, the LC-MIPs indicated potentials for oral administration due to the innovative combination of floating and controlled release properties.

Polymer Network Liquid Crystal (PNLC) Lenticular Microlens Array With No Surface Treatment

A polymer network liquid crystal (PNLC) lenticular microlens array with no surface treatment is prepared. Before polymerization, the LC and diacrylate monomers are reoriented with gradient refractive index distribution by a fringing field. After polymerization, the oriented LC is stabilized by the polymer network. The prepared PNLC lenticular microlens array is optically anisotropic. Without surface treatment, the device fabrication is simplified, and it can present almost the same optical performance as the PNLC lenticular microlens with surface treatment. Integrating with a 90 $^\circ $ twisted-nematic LC cell, the PNLC lenticular microlens array can be switched between a focusing state and non-focusing state. Such a PNLC lenticular microlens array has potential application in switchable 2D/3D displays.

Reactive mesogen photoalignment on photopolymerizable composite layer

The volume photoanisotropy (photoinduced birefringence) and surface photoanisotropy (LC photoalignment) of compositions of LC monomer - benzaldehyde polymer upon polarized UV radiation have been revealed and investigated. A high quality of photoalignment is confirmed by an extreme value of birefringence and low imperfection of phase plates fabricated on the basis of LC monomer on composite layer.

Photoinduced Topographical Feature Development in Blueprinted Azobenzene‐Functionalized Liquid Crystalline Elastomers

All‐optical deformation and recovery of complex topographical features is demonstrated within elastic sheets composed of main‐chain type azobenzene‐functionalized liquid crystalline elastomers (azo‐LCEs). The azo‐LCEs are synthesized via an orthogonal, two‐step reaction between commercially available LC monomers and n‐butylamine. By employing surface alignment, the local orientation of the nematic director is spatially complex (“blueprinted”). Exposing the blueprinted LCE films to light as an actinic stimulus generates a photomechanical response which yields reversible shape changes between 2D and 3D shapes. The deformation of azo‐LCEs strongly depends on the azobenzene concentration as well as the network structure (i.e., crosslink density). Blueprinting complex director profiles within azo‐LCEs yield reconfigurable elastic sheets that can be addressed both remotely and selectively which may have benefit in a variety of applications in aerospace, medicine, and optics.

Synthesis, phase behaviour and photo-optical properties of bent-core methacrylate with azobenzene group and corresponding side-chain polymethacrylate

Novel LC monomer and corresponding polymethacrylate are synthesized and their phase behaviour, photooptical properties and photoorientation under polarized-light action are studied.

PB11 静電紡糸法により紡糸した紫外線硬化型液晶性モノマーの特性を付与した微細ファイバーによる液晶配向制御(液晶物理・物性,ポスター発表,2015年日本液晶学会討論会)

PB11 静電紡糸法により紡糸した紫外線硬化型液晶性モノマーの特性を付与した微細ファイバーによる液晶配向制御(液晶物理・物性,ポスター発表,2015年日本液晶学会討論会)

Optical and mesomorphic properties characterisation of chiral liquid crystalline copolysiloxane exhibiting cholesteric and blue phases

A series of liquid crystalline polymers (LCPs) have been synthesised by two cholesteric monomers M1, M2 and a nematic monomer M3. The chemical structures and liquid crystalline properties of the monomers and polymers have been characterised by FTIR, 1H-NMR, differential scanning calorimetry, thermogravimetric analyses, X-ray diffraction measurements and polarising optical microscopy. All LCPs show a high thermal stability with wide mesophase temperature ranges. For polymer P1 bearing only cholesteric LC monomers component, it shows a cholesteric phase, whereas others display a blue phase besides a cholesteric phase. The formation of the blue phase is based on the structures of the polymers and the produced biaxial helix. The glass transition temperature and isotropic temperature of the polymers decrease on heating cycle with increasing the content of M3 in the polymers. The specific rotation values of the polymers are temperature-sensitive. The reflection spectra of polymers P1–P6 show that the maximum reflected wavelengths shift to long wavelength with increasing the content of M3 in the polymer systems. The frequency and intensity of the bands change sharply at the temperature where cholesteric phase changes to blue phase, but they show a weak dependence on temperature in the blue phase.

Synthesis and characterization of fluorinated liquid-crystalline elastomers containing chiral liquid-crystalline crosslinking units

Fluorinated chiral liquid-crystalline elastomers (LCEs) were graft copolymerized by a one-step hydrosilylation reaction with polymethylhydrogenosiloxane, a fluorinated LC monomer 4-(2,2,3,3,4,4,5,5,6,6,7,7,8,8,8-pentadecafluorooctanoyloxy)phenyl 4-(undec-10-enoyloxy)benzoate (PPUB) and a chiral crosslinking LC monomer (3R,3aR,6S,6aR)-6-(undec-10-enoyloxy)hexahydrofuro[3,2-b]furan-3-yl 4′-(4-(allyloxy)benzoyloxy)biphenyl-4-carboxylate (UHAB). The chemical structure, liquid-crystalline behavior and polarization property were characterized by use of various experimental techniques. The effective crosslink density of the LCEs was characterized by swelling experiments. The thermal analysis results showed that the temperatures at which 5% weight loss occurred were greater than 250°C for all the LCEs, and the residue weight nearby 600°C increase with increasing chiral crosslinking components in the polymer systems. All the samples showed chiral smectic C mesophase when they were heated. The glass transition temperature and mesophase-isotropic phase transition temperature of fluorinated elastomers increased slightly with increase of chiral crosslinking mesogens in the polymer systems, but the enthalpy changes of mesophase-isotropic phase transition decreased slightly. In XRD curves, all the samples exhibited strong sharp reflections at small angles suggesting smectic layered packing arrangement. These fluorinated chiral LCEs showed 0.1–0.2μC/cm2 of spontaneous polarization with increasing chiral crosslinking component.