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The shape memory effects and photoinduced deformation behaviour of interpenetrating polymer network (IPN) films containing azobenzene liquid-crystalline polymers were investigated.

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Sunlight-driven smart windows were developed with polymer/liquid crystal composites containing donor–acceptor-type azobenzene derivatives.

In a narrow temperature window in going from the isotropic to highly chiral orders, cholesteric liquid crystals exhibit so-called blue phases, consisting of different morphologies of long, space-filling double twisted cylinders. Those of cubic spatial symmetry have attracted considerable attention in recent years as templates for soft photonic materials. The latter often requires the creation of monodomains of predefined orientation and size, but their engineering is complicated by a lack of comprehensive understanding of how blue phases nucleate and transform into each other at a submicrometer length scale. In this work, we accomplish this by intercepting nucleation processes at intermediate stages with fast cross-linking of a stabilizing polymer matrix. We reveal using transmission electron microscopy, synchrotron small-angle X-ray diffraction, and angle-resolved microspectroscopy that the grid of double-twisted cylinders undergoes highly coordinated, diffusionless transformations. In light of our findings, the implementation of several applications is discussed, such as temperature-switchable QR codes, micro-area lasing, and fabrication of blue phase liquid crystals with large domain sizes., The arrangements of defect lines in liquid crystal blue phases provide promising templates for photonic crystals. Here Liu et al. investigate in detail how inter-phase transitions proceed, by intercepting nucleation with on-demand cross linking of a supporting polymer matrix.

Rewritable paper, as an environment-friendly approach of information transmission, has potential possibility to conserve energy and promote a sustainable development of our society. Recently, photonic crystals (PCs) have become a research hotspot in the development of rewritable paper. However, there are still many shortcomings that limit the further application of PC paper, such as slow response sensitivity, short-cycle lifetime, poor storage stability, and so on. Herein, we constructed an optically rewritable azobenzene inverse opals (AZOIOs) with a thin film (ca. 1 μm) plated on an inverse opal structure based on the UV/vis switchable structure color of the sample. The top thin film acts as a protective layer to avoid the large deformation of the pore structure and the bottom inverse opal structure with refractive index/pore structure change that provides reversible structure color. Large, reversible, and rapid bandgap shift (ca. 60 nm, 2 s) of AZOIOs can be repeated more than 100 times under alternating UV/vis irradiation based on isomerization of high content of the azobenzene group. On-demand long-time preservation pattern can be obtained by the appearance of azobenzene's intrinsic color. The proof of concept for rewritable PC paper is demonstrated herein. Such inkless rewritable colorful paper paves a way for developing novel display technology.

Photonic shape memory (SM) polymers based on liquid crystalline blue phase (BP) films have been fabricated by self-assembly and subsequent photopolymerization of liquid-crystal mixtures. These freestanding BP films exhibit narrow photonic band gaps and high reflectivity in the visible wavelength range. Multiple blue-shift colors are achieved by SM programming process at different mechanical pressures. The blue-shift colors can be attributed to a decrease of effective BP pitch along the viewing direction caused by the compressed deformation of the BP films, which are confirmed by a three-dimensional interometric profile. The deformed BP films can recover to their original shapes and reflecting colors by heating the polymer films to temperatures above the glass-transition temperature. Quantitative relationships between the shape change and optical response are established for understanding this SM effect. What is more, the temporary photonic patterns can be reversibly written and erased for dozens of cycles without apparent degradation, making these freestanding BP films appealing as rewritable photonic papers and optical sensors.

Azobenzene actuators have aroused enormous research interest due to their excellent performance and promising applications in the fields of soft robots, artificial muscles, etc. However, there are still challenges for the fabrication of azobenzene actuators with a sophisticated actuation mode owing to the unitary actuation direction and slow thermal relaxation of

Soft organic lasers with multiwavelength output and high spectral purity are of crucial importance for versatile photonic devices, owing to their monochromaticity, coherence, and high intensity. However, there remain challenges for the achievement of surface-emitting multiwavelength lasing in soft photonic crystals, and the relative mechanisms need to be investigated. Herein, single-, dual-, triple-, and quadruple-wavelength lasers are successfully achieved in dye-doped blue-phase liquid crystal (BPLC) film. The number and wavelength of the lasing peaks can be manipulated by tuning the center of the bandgap, the order parameter of the laser dye, the quality of the resonance cavity, and even the pump energy. For single-wavelength lasing, a lasing peak with an ultranarrow linewidth of 0.04 nm (Q-factor of 13 454) is achieved. Multiwavelength lasing is attained based on the following aspects: i) the narrow bandgaps of the BPLCs with full width at half maximum of 14-20 nm; ii) a laser dye with high gain over a wide wavelength band, having a low-order parameter in the liquid crystal matrix; iii) appropriate relative positions between the reflection and fluorescence peaks; and iv) the highly ordered crystal lattice of BPLC film. The proposed single-to-quadruple-wavelength surface-emitting lasers can be employed as coherent light sources for next-generation optical devices.

Fabrication of liquid-crystalline polymer networks with periodic nanoscale features is highly desired for photonic applications. Here, a printable photonic polymer coating has been fabricated from a monodomain liquid crystalline blue phase (BP) network. The BP polymer coating with high reflectivity is covalently linked to the glass substrate, which can be patterned by using an LC-ink to swell the network. The degree of swelling depends on the printed amount of LC-ink which can be controlled through adjusting the voltages of the inkjet printer. Arbitrary multicolour patterns covering the visible spectrum from 451 to 618 nm can be printed and erased multiple times, making these BP polymer coatings promising as rewritable photonic papers and responsive photonic materials.

Here, a facile method is put forward to fabricate freestanding, large-domain blue phase (BP) films based on self-assembly technology. This fabrication method enables the formation of BP domains with large-scale lateral dimensions of ∼230 μm, which exhibit sharp photonic bandgaps with high reflectivity. In addition, the large-domain BP structures with good optical performances can be preserved after photopolymerization. What is more, the long-range periodic nanostructures of double-twist cylinders can be directly visualized through transmission electron microscopy, providing a powerful tool to investigate BP structures at the nanoscale. Furthermore, dual-wavelength lasing is achieved by doping the large-domain BP films with fluorescent dyes, which is firstly observed in BP materials.

Liquid crystal elastomers, serving as a new kind of intelligent material, have demonstrated important application in the fields of microactuators, artificial muscles, microfluid transportation and intelligent sensors by virtue of their characteristics of spontaneous reversible deformation under external field stimulation. In this paper, we have reviewed the recent research progress of liquid crystal actuator materials, including of phototropic, thermotropic, photothermal and solvent/humidity-based liquid crystal actuators. The processing techniques, deformation response and actuation mechanism of liquid crystal elastomers were discussed and the relative application prospects were put forward. This work will provide important insights for the construction and development of novel liquid crystal optical devices.

We prepared crosslinked azobenzene main-chain liquid-crystalline polymers (MCLCPs), in which the exchange of crosslinks can be brought about by transesterification reactions. The exchangeab...

We prepared 2 types of crosslinked liquid-crystalline polymers (CLCPs) (polyacrylates) with the same side-chain length but a different position of an azobenzene moiety in the side chain. We...

Poly(4-vinylpyridine) (P4VP) brushes were grafted onto a substrate via Cu(0)-mediated atom transfer radical polymerization and 1-pyrenebutyric acid (PBA) was incorporated into the brushes t...

Janus/gradient actuating materials have become promising candidates for actuating devices. The fabrication of functional Janus gradient actuators remains a challenge. This paper presents a facile fabrication of a hydrophilic/hydrophobic Janus inverse opal actuator via gradient infiltration. The Janus characteristics of the fabricated actuator were attributed to gradient infiltration along the thickness of the film caused by the gradient light intensity and the distinct polymerization behavior of ionic liquids and methyl methacrylate in the methanol system. The Janus film demonstrated directional bending upon water vapor adsorption, with a bending angle approaching 1440° in 4 s, accompanied by structure color/optic signal alteration. The actuating behaviors were effectively modulated by changing the composition of the film and the solvent system. Promising applications of this Janus solvent actuator were demonstrated in two sets of tests: driving an engine and lifting cargo. This work provides insight into the design and fabrication of multifunctional humidity-actuating materials.

The change in shape inducible in some photo-reversible molecules using light can effect powerful changes to a variety of properties of a host material. The most ubiquitous natural molecule for reversible shape change is the rhodopsin–retinal protein system that enables vision, and this is perhaps the quintessential reversible photo-switch. Perhaps the best artificial mimic of this strong photo-switching effect however, for reversibility, speed, and simplicity of incorporation, is azobenzene. This review focuses on the study and application of reversible changes in shape that can be achieved with various systems incorporating azobenzene. This photo-mechanical effect can be defined as the reversible change in shape inducible in some molecules by the adsorption of light, which results in a significant macroscopic mechanical deformation of the host material. Thus, it does not include simple thermal expansion effects, nor does it include reversible but non-mechanical photo-switching or photo-chemistry, nor any of the wide range of optical and electro-optical switching effects for which good reviews exist elsewhere.

Crosslinked liquid-crystalline polymers (CLCPs) containing photochromic moieties show macroscopic deformation upon irradiation with light. This conversion of light energy into mechanical work is attributed to photosynergetic amplification of changes at multiscale: from nano to macro. This chapter focuses on recent progress of photomobile polymer materials to achieve versatile design as soft actuators. Three approaches are detailed: incorporation of amorphous polymers into CLCPs to control mechanical and photoresponsive properties, reshaping of CLCPs into various three-dimensional architectures through the rearrangement of network structures, and application of two-photon absorption processes to enhance the spatial selectivity of photoactuation.

Composite systems of liquid crystals (LCs) and polymers have been extensively studied in various forms such as polymer-dispersed LCs and polymer-stabilised LCs. Blending LCs and polymers is an effective approach to design functional materials with stimuli responsiveness and durability. Here, we show the development of a novel composite material with crosslinked azobenzene LC polymer (PAzo) and poly(dimethylsiloxane) (PDMS) aiming at the improvement of photomobile polymer materials in mechanical properties. The composite films were prepared by photopolymerisation of azobenzene monomers in PDMS elastomers. By forming phase separated structure, in which PAzo chains were dispersed in PDMS matrix, fracture strain of photomobile polymer materials was significantly enhanced. The composite film showed macroscopic bending upon irradiation with UV light. This result implies that PAzo domains in polymer matrix can work as microactuators to afford macroscopic deformation of the whole film. The further improve...

We developed a novel block copolymer composed of poly(ethylene oxide) (PEO) and polymethacrylate functionalized with liquid–cryst-alline oligothiophene by using the atom transfer radical polymeriza...

Crosslinked liquid-crystalline polymers (CLCPs) containing azobenzene moieties show reversible macroscopic deformation upon irradiation with light. The deformation of CLCPs strongly depends on alig...

We prepared crosslinked azotolane liquid-crystalline polymer (LCP) films doped with a stilbene derivative (two-photon chromophore) utilizing an interpenetrating polymer network (IPN) structure. The IPN films bend toward the light source upon irradiation with femtosecond laser pulses at 600 nm, which can excite the stilbene derivative by two-photon absorption. The bending speed of the IPN films increases with the square of the laser pulse intensity, which is compelling evidence for the two-photon processes.

The chemical functionalization of nano-carbon materials such as single-walled carbon nanotubes (SWNTs) and graphene by metal complexes has attracted much attention due to the multitude of potential applications in efficient energy-conversion and -storage devices. The solubilization and single-chirality separation of SWNTs by surface modifications is a useful approach to manipulate SWNTs in the liquid phase. In this study, several Ru and Fe complexes containing two terminal quadruple hydrogen-bonded (H-bonded) ureidopyrimidinedione (UPy) groups were synthesized (Ru-1, Ru-UPy, and Fe-UPy) to form H-bonded supramolecular polymers by self-association. In order to control the solubility of these complexes in nonpolar solvents, Ru-UPy and Fe-UPy were endowed with long alkyl side chain groups in the coordinated 2,6-bis(benzimidazol-2-yl)pyridine ligand, while Ru-1 and Ru-2 do not contain such long alkyl chain groups. AFM measurements revealed that Ru-1, Ru-UPy, and Fe-UPy form a fiber-like network morphology on HOPG surfaces, arising from the H-bonded aggregation. However, only Ru-UPy and Fe-UPy are able to solubilize SWNTs effectively upon simple sonication in chlorobenzene. After the solubilization of a CoMoCAT® SWNT in chlorobenzene using Ru-UPy or Fe-UPy, UV-Vis-NIR spectra showed sharp peaks at 996 and 1150 nm, which were attributed to (6, 5) and (7, 6)-SWNTs. The Raman spectra of the solubilized SWNTs revealed peaks that were attributed to the radial breathing mode (RBM), which suggests an enrichment of semiconducting SWNTs, i.e., Ru-UPy and Fe-UPy are able to selectively solubilize semiconducting SWNTs. Cyclic voltammograms of films of SWNTs covered with Ru-UPy or Fe-UPy on ITO electrodes showed a well-defined adsorbed Ru(ii/iii) or Fe(ii/iii) wave. Upon addition of acid, the redox response from the adsorbed H-bonded Ru-UPy and Fe-UPy disappeared and only SWNTs were left on the ITO electrode. Moreover, the Ru-UPy/SWNT and Fe-UPy/SWNT hybrids exhibited non-linear I-V characteristics.

A reversible solvent-sensitive actuator with a continuous bending/debending process is fabricated by over-infiltration of liquid crystal monomers into a colloidal template and subsequent photopolymerization. The fabricated actuator exhibits a maximum bending angle of 1080° in 1.58 s in dichloromethane, accompanied with successive debending in 0.32 s. The behavior of the actuator can be modulated by changing the solvent type, film thickness/length and molar ratio of A6OCB/C6M. This study will provide an important experimental and theoretical basis for the development of novel actuators.

This paper demonstrates multi-functional optical properties of organosilane-polymerized carbon dot inverse opals, such as tricolor-fluorescence, fluorescence enhancement, multi-color micro-patterns for anti-fake applications and a thermally-induced blueshift of bandgaps. It is of significance for the design and fabrication of novel optical devices.

We developed photomobile polymer materials with interpenetrating polymer network (IPN) structures composed of crosslinked liquid-crystalline azobenzene polymer (PAzo) and poly(dimethylsiloxane) (PDMS). By introducing PDMS into a PAzo template network, IPN was formed without disturbing the alignment of mesogens in the PAzo network. The films showed macroscopic bending behavior upon irradiation with UV and visible light. Although the IPN film showed a phase separated structure, the bending speed was significantly enhanced compared with the pristine film of PAzo, thanks to the soft nature of PDMS. The present method of preparing IPNs can be a promising approach to combine PAzo with various polymers and enhance the mechanical and photoresponsive properties.

We prepared a block copolymer composed of polythiophene (PT) with cinnamate groups and poly(ethylene oxide) (PEO), which are connected through a cleavable acetal bond, aiming at constructing donor/acceptor heterostructures through post deposition of acceptor molecules into donor template networks. The block copolymer films showed phase-separated structures with domain sizes of 10–100 nm. Irradiation with UV light afforded crosslinked films through [2+2] cyclodimerization of cinnamate groups. Then, PEO was removed by acidic cleavage of the acetal bond, yielding PT template networks. Taking advantage of the insoluble networks, a fullerene derivative was deposited into the PT templates through a spin-coating process to form donor/acceptor heterostructures. The introduction of the fullerene derivative was confirmed by UV-Vis absorption and fluorescence spectroscopy. This strategy of depositing acceptor molecules into donor template networks, instead of spin-coating from donor/acceptor blend solutions, could be applied to improve the phase-separated structures and power conversion efficiencies of polymer solar cells.

This paper presents a unique lyophilic but nonwettable property of organosilane-polymerized carbon dots inverse opals photonic crystals (SiCDPCs) with closed-cell structure. Little stopband shift was observed for the SiCDPCs when being immersed into the solvents such as isopropanol, olive oil, DMSO, hexane, silicone oil, ethanediol, etc. but keeping lyophilic property. This could be attributed to the combined effect of closed-cell structure and the unique chemical composition of SiCDPCs. Furthermore, more than 30 kinds of organic solvents had been investigated, it was found that there were two kinds of factors that affected the stopband shift upon solvent's immersing; one was the polarity of solvent, and the other one was the viscosity of solvent. That is, mainly nonpolar or high viscosity solvents showed lyophilic but nonwettable property. The distinct solvent-responsive behaviors of the SiCDPCs toward polar/nonpolar solvents had been utilized for the fabrication of 2D/3D pattern. Additionally, the as-prepared SiCDPCs showed improved optical limiting property, excellent low-temperature resistance, and abrasion tolerant property. It is of great importance for the development of multifunctional novel coating materials and creation of novel optical devices.

We have synthesized a photo-crosslinkable polythiophene copolymer functionalized with a cinnamate moiety to improve the stability of organic photovoltaic (OPV) cells. The active layer of OPV cells is generally bulk heterojunction (BHJ) that consists of two or more organic semiconductors. When BHJ forms a micro-phase-separated structure with a blend of two organic materials, its structure inclines to change into a macro-phase-separated one after some time. To stabilize the BHJ morphology, we used a crosslinkable polymer containing a cinnamate moiety. The copolymer film became insoluble after UV irradiation because of [2+2] dimerization of the cinnamate groups.

We synthesized polymers containing a liquid-crystalline (LC) oligothiophene moiety in the side chain. This oligothiophene shows LC behavior between 101°C and 194°C in its original form, while when incorporated into the side chains of a polymer, the resultant polymer showed a nematic phase in a much wider temperature range. Thin films of these polymers showed nano-phase-separated structures with domain sizes of 15–40 nm upon annealing.

Crosslinked liquid-crystalline polymers (CLCPs) show unique behavior of deforming macroscopically when stimulated with heat, electricity and light. However, they cannot be remolded and reshaped once prepared. Here, we designed crosslinked polysiloxane with side chain mesogens that contain exchangeable crosslinking points based on transesterification between phenyl benzoates and hydroxy groups. After the formation of a polymer network, a base catalyst was introduced into the CLCP. When heated at 80°C, a piece of the CLCP was reshaped into a film and separate pieces of the CLCP were fused together, indicating that the CLCP is remoldable.

We developed interpenetrating polymer networks (IPNs) composed of a crosslinked azobenzene liquid-crystalline polymer (PAzo) and poly(alkyl methacrylate)s (PAMAs). When irradiated with UV and visible light, the IPN films showed reversible bending. The photoresponsive and mechanical properties of PAzo films were significantly enhanced by incorporation of the PAMA components.

We prepared photomobile polymer materials composed of crosslinked azobenzene liquid-crystalline polymers (LCPs) and methacrylates with interpenetrating polymer network (IPN) structures, and explored their photoresponsive behavior. The IPN films exhibited reversible bending upon photoirradiation. In addition, the durability of the IPN films was much higher than that of the pristine crosslinked azobenzene LCP films.

Vernetzte flussigkristalline Polymermaterialien, die sich bei Bestrahlung mit Licht makroskopisch verformen, wurden eingehend erforscht, vor allem wegen ihrem Anwendungspotential fur Mikroaktuatoren und mikrofluidische Bauteile. Die Grundbewegungen dieser Materialien sind Kontraktion/Expansion und Krummung/Entspannung, die in Polysiloxanen und Polyacrylaten mit photochromen Einheiten hauptsachlich beobachtet werden. Andere ausgeklugelte Bewegungen, wie Drehung, Schwingung, Rotation und Parallelverschiebung, wurden ebenfalls realisiert. In den vergangenen Jahren wurden Anstrengungen unternommen, um die photoresponsiven und mechanischen Eigenschaften dieser neuen Klasse von Materialien durch die Modifizierung von Molekulstrukturen, die Entwicklung neuer Herstellungsverfahren und den Aufbau von Verbundstrukturen zu verbessern. In diesem Kurzaufsatz geben wir einen Uberblick uber Strukturen, Funktionen und Wirkmechanismen photomobiler Materialien und stellen die neuesten Fortschritte auf diesem Gebiet vor.

Various fabrication methods of photomobile polymer materials containing photochromic moieties have been developed to improve their photoresponsive and mechanical properties. Here, we newly prepared photomobile polymer materials with interpenetrating polymer network (IPN) structures. The IPN films, which are composed of azobenzene liquid crystalline polymer (LCP) and polymethacrylates, showed reversible bending behavior upon exposure to UV and visible light. Bending speed of the IPN films became higher with decreasing glass-transition temperature of polymethacrylate components. The IPN film containing poly(dodecyl methacrylate) showed faster bending than the pristine azobenzene LCP film.

Orientation control of ordered materials would not only produce new physical phenomenon but also facilitate the development of fancy devices. Discotic liquid crystals (DLCs) form 1D charge transport pathway by self-organizing into columnar nanostructures via π-π stacking. However, controlling the electrical properties in such nanostructures with some direct and instant way is a formidable task for their high viscosity and insensitivity to external stimuli. Herein, the arbitrary control over electrical conductivity of such columnar nanostructures is achieved with UV light by incorporating DLCs with molecular motors. Highly ordered DLC microstripe arrays are generated on desired substrate through a capillary bridge dewetting strategy. The conductivity of the microstripes could be continuously modulated by 365 nm light due to the influence of molecular motion under UV irradiation on the electron orbital overlap of columnar nanostructures. This is so because the disorder degree of the DLC molecules is associated with the intensity of UV light and the doping concentration of molecular motors. Moreover, the device shows memory effect and reversible conductivity change. The DLC microstripe arrays are very promising for the applications in UV detectors, memory devices, optical switches, and so on.