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This study investigates and develops for the first time an electrically tunable liquid-crystal–polymer composite laser with a symmetric sandwich structure. This structure includes two identical pol...

Chameleons, which are among the poikilotherms, can rapidly change color for camouflage, communication and thermoregulation. These cold-blooded animals physiologically shift color through the active tuning of lattices of guanine nanocrystals within a superficial thick layer of dermal iridophores. This active tuning can be described as alternating different refractive indices of nano-reflectors, thereby generating interference of light waves. The self-regulation of the skin behind its dynamic color changing ability makes it the ultimate “biomimetic surface” and a continued source of inspiration. We presented a deformation-color multi-responsive actuator whose response is controlled by delicate light to mimic these adaptive functions. This soft smart material is developed by well-aligned cholesteric liquid crystal elastomers (CLCE). It performs a 185 nm wavelength shift of selective reflection and is switched by reacting to exposure time. Effective optical management is critical for the operation of many modern technologies. These results demonstrate distinctive potential opportunities for LC elastomers to control light, thereby enabling new applications of modern technologies to textiles, optics, and architecture.

Orientational structure transitions due to a photoinduced surface anchoring modulation were achieved and investigated in the case of NLC microdroplets placed between glycerol and solid surface. The boundary conditions at NLC-glycerol varied under the light action on the dendromer dopant containing azobenzene terminal fragments. At the same time, the NLC had a strong planar anchoring with the polyimide treated substrate. Numerical simulation of the observed orientational structures in NLC microdroplets were carried out.

Recently, GaTe and C2N monolayers have been successfully synthesized and show fascinating electronic and optical properties. Such hybrid of GaTe with C2N may induce new novel physical properties. In this work, we perform ab initio simulations on the structural, electronic, and optical properties of the GaTe/C2N van der Waals (vdW) heterostructure. Our calculations show that the GaTe/C2N vdW heterostructure is an indirect-gap semiconductor with type-II band alignment, facilitating an effective separation of photogenerated carriers. Intriguingly, it also presents enhanced visible-UV light absorption compared to its components and can be tailored to be a good photocatalyst for water splitting at certain pH by applying vertical strains. Further, we explore specifically the adsorption and decomposition of water molecules on the surface of C2N layer in the heterostructure and the subsequent formation of hydrogen, which reveals the mechanism of photocatalytic hydrogen production on the 2D GaTe/C2N heterostructure. Moreover, it is found that in-plane biaxial strains can induce indirect-direct-indirect, semiconductor-metal, and type II to type I or type III transitions. These interesting results make the GaTe/C2N vdW heterostructure a promising candidate for applications in next generation of multifunctional optoelectronic devices.

Supramolecular β-cyclodextrin (β-CD) was used as a soft template for the fabrication of long silver nanowires. A novel design using self-assembled β-CD for the reduction of silver ions was studied. The concentrations of iron chloride, silver nitrate, and the template were controlling factors for the growth of the silver nanowires. Iron chloride was used to accelerate and facilitate the formation of the silver nanowires and inhibit oxidative etching. However, an excessive concentration of Fe+3 resulted in etching of the silver nanostructures. Furthermore, the silver concentration was another controlling factor. The length of the silver nanowires increased as the concentration of silver cations increased. Nevertheless, an excess concentration of silver cations formed various silver crystalline structures. In this study, the optimal ratio between iron chloride and silver nitrate was determined to be 1:13.3. A maximum length of 20 µm was achieved using a concentration of 0.23 M for the soft template. Moreover, the junction of two growing silver nanowires was observed, forming a long fused nanowire, and some significant boundaries were observed. The observed results were further confirmed using scanning electron microscopy (SEM) and transmission electron microscopy (TEM) analyses. X-ray diffraction (XRD) and energy dispersive spectrometer (EDS) analyses were used to indicate the presence of silver and the formation of crystalline materials.

Two sequential transformations of the orientational structure in nematic liquid crystal droplets containing a dendrimer additive (nanosized macromolecules with light-absorbing azobenzene terminal moieties) under light irradiation in the UV–blue spectral range were investigated. The origin of these transitions is in the change of the boundary conditions due to photoisomerization of the dendrimer adsorbed onto the liquid crystal–glycerol interface. It was shown that the photoisomerization processes of dendrimer molecules in a liquid crystal are accompanied by a spatial rearrangement of their azobenzene moieties, which is the key point in the explanation of the observed effects.

A structured broad-band photonic film is fabricated by a novel method using multiple gradient UV-induced polymerization in the presence of cholesteric liquid crystals (CLCs). Here, imprinting and broadening of the reflection band of chiral nematic mesophase cells are achieved via controlled UV polymerization. The intensity gradient of UV light is modified by the distance between UV lamp and sample cell, which affects the polymerization rate and leads to the formation of imprinted helical constructions with different pitches. In this study, a comparison of new design process with traditional UV polymerization process is carried out. After seven cycles of gradient UV polymerization, the imprinted photonic construction exhibited a broadened reflection band and Bragg reflection, even for isotropic materials. Because of this, the reflection bandwidth showed a 70% improvement. Additionally, two stacked imprinted cells with different pitches can reflect incident light with a bandwidth over the visible wavelength range of 480–680 nm. A broad-band photonic polymer film can be imprinted using multiple gradient UV photopolymerization in the presence of CLCs. Forming a UV intensity gradient and controlling the rate of photopolymerization are key factors in broadening the reflection band. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017

Two structurally isomeric azobenzene- and cholesteryl-based derivatives with varying alkyl chain lengths were developed as ALS-type gelators (N2 and N4) and synthesized and characterized spectroscopically. Of the two, N4 acted as a more efficient gelator than N2 since N4 could gel a larger number of solvents. The critical gelation concentration (CGC) of N4 was found to be less than that of N2 in the same solvent system. The morphological analyses of both gelators using SEM and TEM revealed that N4 exhibited self-assembled fibrous structures, whereas N2 exhibited spherical nanoparticles. The van der Waals interactions between the cholesteryl units, hydrogen bonding between the amide linkages and π–π stacking between the azobenzene units provided the driving force for the aggregation and gel formation. These driving forces were evidenced by temperature dependent 1H-NMR, FTIR and XRD analyses. Increasing the temperature of the gels shifted (upfield and downfield) the protons in the 1H-NMR spectra as well as the absorption bands in the FTIR spectra indicating that the intermolecular forces between the molecules became disrupted and caused gel → sol transitions. These transitions were reversible after cooling to room temperature. Similarly, the gel → sol transitions could be triggered by UV light (due to trans/cis isomerization); however, the transition was irreversible in the presence of visible light due to the formation of the more stable cis isomer. Hence, the gel state could be retained by heating and cooling the cis-conformation. In addition, the length of the molecule as determined by simulation software was found to match the values observed from the XRD analysis, and the interlayer distances were found to be 1.78 and 1.85 nm for N2 and N4, respectively. Based on this evidence, an aggregation mechanism was proposed. The differential scanning calorimetry (DSC) and polarized optical microscopy (POM) results revealed that both gelators exhibited grainy nematic mesophase textures during the heating and cooling cycles. These gelators underwent phase-selective gelation in the solvent mixtures containing gelling and nongelling solvents, which demonstrated the applicability of these gelators for the separation and purification of solvents.

Liquid crystals (LCs) are distinctive materials that are applicable to a wide range of disciplines, such as continuum mechanics, optics of anisotropic media, statistical physics, and crystallography. The diverse structures and eye-catching topological defects of LCs in confined geometries are affected by nematic elasticity, chirality, and surface anchoring. Herein, we report the formation and detailed configuration of cholesteric LC (CLC) microdroplets with different pitches pierced by electrospun poly(methyl methacrylate) microfibers. Two kinds of surface anchoring, namely, homeotropic anchoring at the air–CLC droplet interface and planar anchoring at the fiber–CLC droplet interface, coexist in this system. By controlling temperature and light irradiation, the system exhibits thermal- and photo-dependent LC morphological and topological evolutions. The observed structures are complemented by numerical simulations of possible director fields decorated by defects. The externally controllable CLC necklaces constitute extraordinary systems for exploring the morphology and topological defects and open a route for applications in topological remote control, nanoscience, biomedical research, and the development of devices based on topologically structured soft media.

Three high-resonance core compounds, BHC-6, BHC-11 and BHC-cho , were synthesized. The morphologies of the self-assembled xerogels of the synthesized compounds were studied using SEM and TEM. The molecular interactions and the formation of asymmetric constructions were investigated using temperature-dependent 1 H NMR spectroscopy and circular dichroism spectrometry, respectively. The induction of an asymmetric helical structure was further confirmed using TEM. The results show that increasing the resonance length strengthens intermolecular forces, leading to the formation of gels. A chiral environment produces a steric field effect, leading to the formation of asymmetric constructions. The interactions between functional groups were further confirmed using 2D nuclear overhauser effect spectroscopy NMR. The reversible E – Z isomerization and dimer formation of cinnamoyl derivatives were investigated using UV–vis and fluorescence spectrometry, relatively.

A liquid crystal elastomer (LCE) film is successfully deposited with a terahertz metamaterial using thermal evaporation via a programmed electronic shutter and high-efficiency cooling system. The transmittance of the metamaterial at its resonance frequency is monotonically increased from 0.0036 to 1.0 as a pump beam bends the LCE film, so the metamaterial has a large switching contrast of 277 at the frequency. The monotonic increase in the resonance transmittance arises from the constant resonance frequency of the metamaterial at the transmittance modulation and depicts that the metamaterial-deposited LCE film can continuously tune the transmitted intensity of a terahertz beam. The metamaterial-deposited LCE film has potential in developing continuously tunable intensity modulators with large switching contrasts for the application of terahertz imaging and terahertz communication. Therefore, the thermal evaporation expands the application of metamaterials and improves their optical properties.

An infrared (IR) reflector that has ultra-wide reflection band and high reflectance was successfully fabricated based on an enantiomorphic chiral polymer composite template-made method involving UV-curing, washing-out, stacking, and refilling. In this study, an IR reflector reflecting >80% of incoming solar IR light from 800 nm to 1500 nm and retaining acceptable transmittance in the visible region is demonstrated. This undertaking is achieved by stacking two enantiomorphic double-polymerized chiral polymer templates with large longitudinal pitch gradients as a composite template cell designed for the near-IR region. Heat insulation test reveals that the temperature can be effectively lowered by 2 °C–3 °C by using the IR reflector, thereby indicating that a considerable amount of incident heat could be isolated and a significant amount of energy could be saved by cooling. The sample has potential in green and military applications, such as energy-saving green windows and anti-IR devices.

A new series of symmetric, bis-cholesteryl-appended, isosorbide derivatives (BCIE, BCIC2 and BCIC4) were designed as gelators to respond to changes in their environment and were synthesized successfully. Among these derivatives, BCIE can gel a wide variety of organic solvents (23 solvents), suggesting that BCIE acts as a more versatile gelator than BCIC2 and BCIC4. The CGC of the gels varies from 1.53 mM in 1-hexanol to 23 mM in pyridine. The results of the gelation ability in different solvents revealed that changing the linking group (ester/carbamate) attached to the cholesteryl units can produce a dramatic change in the gelation behavior of the compounds. The morphology of the as-formed organogels can be regulated by changing the types of organic solvents. The results from electron microscopy studies revealed that the gelator molecule self-assembled into different aggregates, from wrinkled fibers to dense fibers, with the change of solvents. The gels of BCIE in 1-hexanol and 1-octanol exhibited strong CD (circular dichroism) signals, indicating that the gelation induced supramolecular chirality in these gel systems. Secondary forces of van der Waals and π-π stacking (from both 1,2,3-triazole and aromatic units) played important roles in the aggregation of compounds in the solvents according to FTIR and variable temperature (1)H-NMR analysis, and a mechanism for the gel formation was proposed. The gel-to-sol phase transition can be triggered by the addition of trifluoroacetic acid (TFA), and the gel state was obtained slowly (after 1 day) when neutralizing with triethyl amine (TEA), which indicated that the sol ⇄ gel phase transitions are tunable by pH, which is further supported by (1)H-NMR and SEM analysis. In addition, the gel stability of BCIE was investigated using Cu(2+), Cd(2+), Ag(2+), Fe(3+), Hg(2+), Mg(2+), Pd(2+), Al(3+) and Zn(2+), and the results showed that the gel-to-sol phase transition process could be selectively controlled by interaction with Pd(2+) and Zn(2+) because complexation with 1,2,3-triazoles destroyed the interactions between the triazoles, collapsing the gel, which was further evidenced by (1)H-NMR and SEM analysis. However, the gel stability of BCIE was enhanced by the addition of Pd(2+) and Zn(2+) in the presence of pyridine, whereas the gel collapsed in other solvents, which may be due to the chelating effect of the pyridine moiety. Another interesting feature of this gel is that when using the gelator as a stabilizer, stable water in oil (W/O) gel-emulsions were created, in which styrene can be used as the continuous phase and water as the dispersed phase with the stabilizer in the continuous phase of only 2% (w/v). Gel-emulsions were observed with any ratio of water to styrene.