A series of photomechanical fibers was fabricated with a thermal drawing method by using liquid-crystalline random copolymers containing azobenzene and biphenyl groups in side chain. After being post-cross-linked under mild conditions, these fibers showed photoinduced bending motion away from the light source even though homogeneous alignment of mesogens was observed along the drawing direction. This abnormal photoinduced deformation of the obtained fibers is far different from previously reported light-directed motions about liquid-crystalline fiber and film materials. The interesting photomechanical deformation can be ascribed to the surface volume expansion caused by photoisomerization of azobenzene moieties. Then the photoinduced bending behaviors of these fibers containing different azobenzene concentrations and cross-linking densities were systematically investigated, suggesting that the location of photoresponsive azobenzene played an important role in deciding their photomechanical behaviors. This provides one convenient way of controlling over the photoinduced bending direction through the location of light-active moieties in side chain or cross-linker. In addition, irradiation of visible light accelerated the recovery of bent fibers. These fibers possess quick response, large deformation, and good thermal stability, indicating their promising applications for smart devices and energy conversion devices.

In this paper, a series of novel active silicone–oligomers (PMDM) of high refractive index (RI) with dual reactive moieties (Si–H and S–H) synthesized by nonhydrolytic sol–gel condensation are reported for the first time. The RI of the oligosiloxane can be effectively increased from 1.55 to 1.65 by varying the feed ratio between methyldimethoxysilane (MDMS) and 3-mercaptopropylmethyldimethoxysilane (MMDS). Additionally, via “thiol–ene” click chemistry and the subsequent hydrosilylation reaction under a Pt catalyst, a transparent siloxane-polymer film with enhanced refractive index (1.59) and excellent thermal stability (T5% = 381 °C) was facilely synthesized and characterized, which in turn effectively substantiated the reactivity of the dual reactive moieties in PMDM. Such active oligomers would be useful chemical intermediates and the easily processed materials have great potential in modern optical/photonic applications such as waveguides, lasers or light emitting diodes.

•Micellization induced fluorescence in azo-containing block copolymer is investigated.•The mechanism relies on self-organization structure of the block copolymer.•The acquired fluorescence intensity can be adjusted by UV, pH and temperature.One amphiphilic diblock copolymer poly(NIPAm-b-M6AzCOONa) with well-defined structure was synthesized by RAFT polymerization, in which N-isopropylacrylamide (NIPAM) was introduced as one thermoresponsive unit, and 6-[4-(4-sodium carboxylatephenylazo)phenoxyl]hexyl methacrylate (M6AzCOONa) was designed as pH-, UV-responsive and fluorescent units. The block copolymer was non-fluorescent in good solvent, but showed fluorescence emission when it formed micelle-like structures in water. The acquired fluorescence can be adjusted by UV or pH, which was strongly related to the aggregation tightness and size of the micelles. The block copolymer also showed reversible fluorescent enhancement in a large range of pH value (pH = 3–11) driven by thermally-induced coil-to-globule transition due to the existence of the PNIPAm block, which leads to a more closely-tightened aggregation of azobenzene moieties. These multiple-responsive fluorescence behaviors enable the amphiphilic block copolymer to find its applications for wide-pH-range fluorescence thermometer and fluorescence probe.

For converting light energy into electricity, an optical pendulum generator was designed by combining photomechanical movement of liquid-crystalline actuator (LCA) with Faraday’s law of electromagnetic induction. Bilayer cantilever actuators were first fabricated with LDPE and LCA. Their photomechanical movement drove the attached copper coils to cut magnetic line of force generating electricity. The output electricity was proportional to the changing rate of the magnetic flux, which was greatly influenced by light intensity, film thickness, and sample size. Continuous electrical output was also achieved. This simple strategy may expand applications of photoactive materials in the capture and storage of light energy.Keywords: electromagnetic induction; liquid-crystalline actuator; optical pendulum generator; photoactive materials; photomechanical materials;

Photoresponsive lamina and flexible graphene oxide/polymer nanocomposite films were fabricated using a simple solution casting method. Fast, stable, and reversible photomechanical behavior of the nanocomposite films upon irradiation with visible light was observed based on the photothermal effect of graphene oxide and the shape memory effect of the polymer matrix. According to the principle of equilibrium apparatus, light-powered tumbler movement was achieved in these films by imitating the structure of a wobbly man. Although photodriven contraction, expansion, bending, twisting, oscillation, and cilia movement have been realized in photomechanical materials, novel forms of complicated motion are still a bottleneck problem limiting their practical applications. This work would have a significant impact on photomechanical materials in device applications for advanced functions.Keywords: graphene oxide; photoinduced 3D movement; photothermal effect; polymeric nanocomposites; shape memory effect

To take full advantage of sunlight for photomechanical materials, NIR–vis–UV light-responsive actuator films of polymer-dispersed liquid crystal (PDLC)/graphene oxide (GO) nanocomposites were fabricated. The strategy is based on phase transition of LCs from nematic to isotropic phase induced by combination of photochemical and photothermal processes in the PDLC/GO nanocomposites. Upon mechanical stretching of the film, both topological shape change and mesogenic alignment occurred in the separated LC domains, enabling the film to respond to NIR–vis–UV light. The homodispersed GO flakes act as photoabsorbent and nanoscale heat source to transfer NIR or VIS light into thermal energy, heating the film and photothermally inducing phase transition of LC microdomains. By utilizing photochemical phase transition of LCs upon UV-light irradiation, one azobenzene dye was incorporated into the LC domains, endowing the nanocomposite films with UV-responsive property. Moreover, the light-responsive behaviors can be well-controlled by adjusting the elongation ratio upon mechanical treatment. The NIR–vis–UV light-responsive PDLC/GO nanocomposite films exhibit excellent properties of easy fabrication, low-cost, and good film-forming and mechanical features, promising their numerous applications in the field of soft actuators and optomechanical systems driven directly by sunlight.Keywords: GO nanocomposites; light-responsive actuator; liquid crystal and nanocomposites; photomechanical materials; polymer-dispersed liquid crystals

Being one of the most fascinating multi-functional materials, photoresponsive liquid crystalline block copolymers (PLCBCs) have attracted much attention because of their light controllable properties of supramolecularly self-assembled structures. These originate from their unique features combining the advanced function of photoresponsive liquid crystalline polymers (PLCPs) with the inherent property of microphase separation of block copolymers (BCs). Benefiting from recent progresses in materials chemistry, diverse PLCBCs have been designed and synthesized by controlled polymerization using different synthetic routes and strategies. Generally, PLCBCs show different performance depending on their self-organization and molecular composition, with the PLCP blocks in the minority phase or in the majority phase. One of the most important properties of PLCBCs is supramolecular cooperative motion, resulted from the interactions between liquid crystalline elastic deformation and microphase separation, which enables them to self-assemble into regularly ordered nanostructures in bulk films with high reliability. These nanostructures contribute to improving the optical performance of polymer films by eliminating the scattering of visible light, in favor of their photonic applications. With the help of liquid crystal alignment techniques, both parallel and perpendicular patterning of nanostructures has been fabricated in macroscopic scale with excellent reproducibility and mass production, which provides nanotemplates and nanofabrication processes for preparing varieties of nanomaterials. Recent findings about PLCBCs including their synthesis, diagram of microphase separation, structure-property relationship, precise control of nanostructure as well as their applications in photonics to nanotechnology are reviewed.

We report a thin-film optical diode written into thin films of a liquid-crystalline polymer (LCP), which is based on the photoinduced LC-to-isotropic phase transition of LCPs. The interference pattern between a collimated and a focused UV laser beam is imprinted as chirped volume-phase gratings in photoresponsive LCP films and no further processing steps like development or liftoff are required for the fabrication. The resultant thin-film device not only possesses the fundamental functions of an optical lens for laser beam focusing, but also shows diode effects with the focusing/defocusing function dependent on the direction of light incidence and orientation of the device. Furthermore, this photonic thin-film lens exhibits a spatially tunable spectroscopic response, revealing a unique physics of secondary excitations of resonance modes of the single-layer LCP waveguide grating structures. This reveals the mechanisms for the focusing/defocusing of laser beams by chirped grating structures. Erasability and reconstructibility of the photoresponsive LCPs guarantee rewritability of the thin-film diode lens.

Recyclable, fast and visible-light responsive polymer-dispersed liquid crystal (PDLC)/graphene oxide (GO) nanocomposite films were successfully fabricated by a combination of solution casting and mechanical stretching. In the PDLC/GO nanocomposite films, one low-molecular-weight nematic LC (5CB) formed a separated phase and GO-dispersed polyvinyl alcohol (PVA) was used as the film matrix. Upon irradiation with visible light, PDLC/GO nanocomposite films showed photomechanical response, bending toward the light source along the stretching direction. Here, GO functioned as the light absorbent and nanoscale heat source to thermally induce a phase transition with 5CB from homogeneous alignment to an isotropic phase. Thus, volume contraction occurred on the surface area of the nanocomposite films due to the photothermal effect of GO, whereas little change took place in the opposite area, resulting in the visible light-induced photomechanical response in a bimetal-like mode. These PDLC/GO nanocomposite films can be potentially applied in soft actuators and micro-optomechanical systems with visible light as the energy source.

Famous for their photoisomerization, azobenzene and its derivatives have been intensively studied as among the most fascinating advanced materials. In particular, azobenzene-containing liquid-crystalline polymer (LCP) materials show unique properties by combining the self-assembly of liquid crystals and photoresponsive performance of chromophores. Here, we highlight their intriguing properties and potential applications from photonics to photodriven motion as well as the novel nanotechnology. The photoresponsive features such as photochemical phase transition, photoinduced alignment and photo-triggered cooperative motion often result in a large modulation of the refractive index, which can be easily fixed in LCP films. This is very advantageous for their photonic applications. Upon forming connections by three-dimensional crosslinking, a large deformation can be photoinduced from the micro to the macro scale, enabling applications as photomechanical and photomobile materials to be found. Upon integrating with the microphase separation of well-defined block copolymers, they exhibit photocontrollable regular nanostructures on the macroscopic scale with excellent reproducibility and mass production, meaning they can be used as nanotemplates for nanoengineering and nanofabrication.

Ultrathin free-standing Janus films were fabricated at air–water interfaces using azopyridine derivatives and poly(acrylic acid) via multi-level self-assembly on molecular and microscopic scales, which showed distinct asymmetric water wetting abilities on different surfaces.

Liquid crystalline microphase formed in PEG/lecithin hydrogels provides suppressed release of hydrophilic drugs but accelerated release for lipophilic drugs, achieving quasi-zero-order release of drugs with different water solubility.

Upon supramolecular self-assembly, novel conductive hybrid nanofibers were successfully fabricated using three amphiphilic salts, azopyridinium, aniline hydrochloride, and alkylbenzenesulfate-based anionic surfactants. The interactions like π–π stacking and ionic bonding among the different compounds played important roles in preparation of these multicomponent hybrid nanofibers. These were demonstrated by measurements of XRD, UV–vis absorption, and FTIR spectra. Interesting conductivity in an order of magnitude of 1 × 10–7 to 1 × 10–5 S/cm was observed in films of the fabricated hybrid nanofibers, which was attributed to the existence of freely movable ions, showing their possible applications as bionanomaterials and nanoelectronic devices. The fabrication processes of the conductive nanofibers might provide references for simulation of nerve fibers in nature.Keywords: azopyridine; conductive materials; hybrid nanofibers; supramolecular self-assembly; π−π stacking interactions;

Being one of the most fascinating multi-functional materials, photoresponsive liquid crystalline block copolymers (PLCBCs) have attracted much attention because of their light controllable properties of supramolecularly self-assembled structures. These originate from their unique features combining the advanced function of photoresponsive liquid crystalline polymers (PLCPs) with the inherent property of microphase separation of block copolymers (BCs). Benefiting from recent progresses in materials chemistry, diverse PLCBCs have been designed and synthesized by controlled polymerization using different synthetic routes and strategies. Generally, PLCBCs show different performance depending on their self-organization and molecular composition, with the PLCP blocks in the minority phase or in the majority phase. One of the most important properties of PLCBCs is supramolecular cooperative motion, resulted from the interactions between liquid crystalline elastic deformation and microphase separation, which enables them to self-assemble into regularly ordered nanostructures in bulk films with high reliability. These nanostructures contribute to improving the optical performance of polymer films by eliminating the scattering of visible light, in favor of their photonic applications. With the help of liquid crystal alignment techniques, both parallel and perpendicular patterning of nanostructures has been fabricated in macroscopic scale with excellent reproducibility and mass production, which provides nanotemplates and nanofabrication processes for preparing varieties of nanomaterials. Recent findings about PLCBCs including their synthesis, diagram of microphase separation, structure-property relationship, precise control of nanostructure as well as their applications in photonics to nanotechnology are reviewed.

A polymer-dispersed azobenzene and GO nanocomposite film was fabricated with shape memory polyurethane as a matrix. Upon mechanical stretching, the nanocomposite film exhibited a photoresponsive triple shape-memory effect by successive exposure to UV and NIR light. Here, azobenzene and GO may act as photo-harvesters for UV and NIR light, respectively, and their photoresponsiveness was transferred to the host polymer films. On one hand, UV light caused the photomechanical motion of azobenzene materials, leading to the photoinduced bending behavior for the composite film. On the other hand, NIR brought about the photothermal effect of GO, heating the film and triggering the thermoresponsive shape-memory of polyurethane. The nanocomposite film showed good mechanical properties, which can be self-healed upon NIR irradiation. Benefitting from these light-directed triple shape-memory properties, simulation of flower blooming and fading was successfully achieved, indicating its potential application as a biomimetic actuator and other functional devices.

Ultrathin free-standing Janus films were fabricated at air–water interfaces using azopyridine derivatives and poly(acrylic acid) via multi-level self-assembly on molecular and microscopic scales, which showed distinct asymmetric water wetting abilities on different surfaces.

Recyclable, fast and visible-light responsive polymer-dispersed liquid crystal (PDLC)/graphene oxide (GO) nanocomposite films were successfully fabricated by a combination of solution casting and mechanical stretching. In the PDLC/GO nanocomposite films, one low-molecular-weight nematic LC (5CB) formed a separated phase and GO-dispersed polyvinyl alcohol (PVA) was used as the film matrix. Upon irradiation with visible light, PDLC/GO nanocomposite films showed photomechanical response, bending toward the light source along the stretching direction. Here, GO functioned as the light absorbent and nanoscale heat source to thermally induce a phase transition with 5CB from homogeneous alignment to an isotropic phase. Thus, volume contraction occurred on the surface area of the nanocomposite films due to the photothermal effect of GO, whereas little change took place in the opposite area, resulting in the visible light-induced photomechanical response in a bimetal-like mode. These PDLC/GO nanocomposite films can be potentially applied in soft actuators and micro-optomechanical systems with visible light as the energy source.

Famous for their photoisomerization, azobenzene and its derivatives have been intensively studied as among the most fascinating advanced materials. In particular, azobenzene-containing liquid-crystalline polymer (LCP) materials show unique properties by combining the self-assembly of liquid crystals and photoresponsive performance of chromophores. Here, we highlight their intriguing properties and potential applications from photonics to photodriven motion as well as the novel nanotechnology. The photoresponsive features such as photochemical phase transition, photoinduced alignment and photo-triggered cooperative motion often result in a large modulation of the refractive index, which can be easily fixed in LCP films. This is very advantageous for their photonic applications. Upon forming connections by three-dimensional crosslinking, a large deformation can be photoinduced from the micro to the macro scale, enabling applications as photomechanical and photomobile materials to be found. Upon integrating with the microphase separation of well-defined block copolymers, they exhibit photocontrollable regular nanostructures on the macroscopic scale with excellent reproducibility and mass production, meaning they can be used as nanotemplates for nanoengineering and nanofabrication.