Photoresponsive Liquid Crystalline Polymers Research Articles

Manipulation of photoresponsive liquid-crystalline polymers and their applications: from nanoscale to macroscale

We summarize the molecular design of photoresponsive liquid-crystalline polymers, manipulation at multiple scales and various applications based on their intrinsic properties, providing an opportunity for future development in this field.

Bending Behaviors in Photoresponsive Liquid Crystalline Polymer Films Derived from a Hockey Stick-Shaped Reactive Mesogen

Bending Behaviors in Photoresponsive Liquid Crystalline Polymer Films Derived from a Hockey Stick-Shaped Reactive Mesogen

Photo-responsive liquid crystalline polymer from a renewable furfural derivative of dimethyl 2,5-furandicarboxylate via catalytic carbonylative esterification

A main chain liquid crystalline polymer has been prepared via melting polycondensation of a bifunctionalized furan monomer (DMFD) from inedible biomass with a photo-responsive azobenzene unit, which can be used in information storage.

Supramolecular hydrogen bond enables Kapton nanofibers to reinforce liquid-crystalline polymers for light-fueled flight

We report fabrication of photoresponsive liquid-crystalline polymers reinforced with highly-oriented Kapton nanofibers with a supramolecular hydrogen bonding interface. To enhance the interfacial strength, hydroxyl groups are introduced into the side chain of azobenzene-containing liquid-crystalline polymers, forming hydrogen bonds with the Kapton nanofibers, directly imaged by nano-FTIR. Interestingly, the composite film exhibits the hierarchical structure of dragonfly wings, while demonstrating relatively high elastic modulus (1.64 GPa), reduced modulus (72.8 GPa), and nanohardness (4.5 GPa); 20–30 times higher than natural dragonfly wings. The enhanced mechanical performance and bilayer structure enables the composite film to exhibit rapid photoresponsive behaviors independent of the direction of illumination, due to an unconventional deformation mechanism arising from the interactions at the fiber-polymer interface. In addition, the flapping frequency and bending angle of the composite films can be continuously tuned for a single device (0.1–5 Hz, and 1.5–15.8°) by modifying the pulsed photoirradiation. The composite films are assembled into an artificial dragonfly device, and the light-driven flight aerodynamics are demonstrated in windy conditions. These not only provide a solution of micro-aircraft wings, but also offer a good bionic model for emulating dragonfly wings.

Four-Dimensional Printed Liquid Crystalline Elastomer Actuators with Fast Photoinduced Mechanical Response toward Light-Driven Robotic Functions.

Remote light exposure of photoresponsive liquid crystalline polymers has drawn great attention over the last years as an attractive strategy to generate mechanical work with high spatial resolution. To tailor these materials into practical engineering devices, it is of key importance to gain control over their morphology and thus precisely program their mechanical response, which must also be fast and relevant in magnitude. In this communication, we report the four-dimensional (4D) printing of azobenzene-containing liquid crystalline elastomers (LCEs) that respond to light. During extrusion of the LCE precursor, mesogen orientation is defined by the needle's moving direction enabling a precise definition of the director, which is later fixed by photopolymerization. Fast mechanical responses have been observed in these 4D printed LCE elements when excited with ultraviolet (UV) light. These 4D printed elements lift objects many times heavier than their own weight, demonstrating a capacity to produce effective work. Photochemical and photothermal contributions to the deformation and force have been identified. Advantageously, the use of blue and UV light excitation enables adjustment of generated forces that can be maintained even in the dark and can be released by light excitation or temperature. The demonstrated ability to generate light-responsive elements quickly delivering sufficient work paves the way for implementing remotely addressed mechanical functions to future soft robotics and engineering.

A Light‐Activated Polymer Composite Enables On‐Demand Photocontrolled Motion: Transportation at the Liquid/Air Interface

Swimmers at liquid/air interfaces have drawn enormous attention because of their potential applications. Described herein is one novel light-driven swimmer based on a bimorph composite structure of a photoresponsive liquid-crystalline polymer network and a commercially available polyimide (Kapton). The motion of the swimmer can be controlled by photoirradiation. The bilayer-structured film shows quickly photoinduced bending towards the Kapton side upon exposure to UV light, and recovers immediately after removal of light. When placed on a liquid surface, the swimmer propels itself continually though rhythmic beating the liquid like a dolphin moving forward with its tail fin. Besides, light-powered rotation of the swimmer is successfully achieved by simply changing the length-width ratio and the irradiation site, mimicking the function of a dolphin's pectoral fin. Combining the forward movement and rotation motion together, on-demand directional control of the photo-driven swimmer can be readily obtained at room temperature, showing promise for miniaturized units for transportation.

Photoresponsive Liquid-Crystalline Polymer Films Bilayered with an Inverse Opal Structure

Photoresponsive Liquid-Crystalline Polymer Films Bilayered with an Inverse Opal Structure

Main chain photoresponsive liquid crystalline polymer synthesized through hydrosilylation

Siloxane based dihydride was reacted with diallyl siloxane for designing a fast photoresponsive LC polymer system having LC phase around room temperature. The nematic LC system with fast trans–cis isomerization behaviour was observed.

Design of polarization-dependent, flexural–torsional deformation in photo responsive liquid crystalline polymer networks

Light responsive materials that exhibit wirelessly actuated, multidimensional deformation are excellent candidates for programmable matter applications such as morphing structures or soft robotics. A central challenge to designing adaptive structures from these materials is the ability accurately predict three dimensional deformations. Previous modeling efforts have focused almost exclusively on pure bending. Herein we examine key material parameters affecting light driven flexural-torsional response in azobenzene functionalized liquid crystal polymer networks. We show that a great deal of control can be obtained by specifying material alignment and actuating the material with polarized light. Insight gained from the theoretical framework here lays the foundation for more extensive modeling efforts to combine polarization controlled flexural-torsional deformations with complex geometry, boundary conditions, and loading conditions.

Meso‐ and Microscopic Motions in Photoresponsive Liquid Crystalline Polymer Films

Photoresponsive azobenzene-containing systems ranging from molecular to macroscopic material levels have greatly been increasing their significance in materials chemistry. This review focuses on the studies on light induced or triggered motions in azobenzene liquid crystalline (LC) polymer films at mesoscopic and microscopic levels. Due to the cooperative nature of liquid crystalline materials, highly efficient photoalignment and photo-triggered migrating motions are realized in mostly repeated manners. Here, recent advances in surface-grafted LC polymer brushes, LC block copolymer films, and LC polymer films that exhibit mass migrations are overviewed. Such newly emerged photoresponsive systems are expected to provide new possibilities and applications in polymer thin film technologies.

Synthesis and photoresponsive properties of two liquid crystalline polymers bearing branched azobenzene-containing side chains

We synthesized two photoresponsive liquid crystalline polymers bearing branched azobenzene-containing side-chains. The side-chain liquid crystal polymers (SCLCPs) were designed to contain two and three azobenzene moieties in each monomeric unit, which were attached to the backbones via a linkage of biphenylene and flexible spacers. The SCLCPs were synthesized by radical polymerization of corresponding methacrylate-based monomers. The polymers were characterized by FT-IR, 1H NMR, UV-vis, GPC and small angle X-ray scattering (SAXS). Both polymers formed the smectic-A mesophase in the LC states, whilst the polymer containing three azobenzene-containing branches in each repeat unit showed a high order mesophase in the lower temperature range. The polymers exhibited trans–cis photoisomerization and photoinduced orientation under light irradiation at suitable wavelengths.

Photodriven, Flexural–Torsional Oscillation of Glassy Azobenzene Liquid Crystal Polymer Networks

AbstractCantilevers composed of glassy, photoresponsive liquid crystalline polymer networks (LCNs) are shown to oscillate at high frequency (∼50 Hz) and large amplitude when exposed to light from a 442 nm coherent wave (CW) laser. Added dimensionality to previously reported in‐plane oscillations is enabled by adjusting the orientation of the nematic director to the long axis of the cantilever yielding in‐plane bending accompanied by out‐of‐plane twisting (flexural–torsional oscillation). The fundamental photoresponse of this class of glassy azobenzene liquid crystal polymer networks (azo‐LCN) is further probed by examining the influence of cantilever aspect ratio, laser intensity, and temperature. The frequency of photodirected oscillations is strongly correlated to the length of the cantilever while the amplitude and threshold laser intensity for oscillation is strongly correlated to temperature.

Liquid‐Crystalline Polymer with a Block Mesogenic Side Group: Photoinduced Manipulation of Nanophase‐Separated Structures

AbstractIn this report, a novel type of photoresponsive liquid crystalline polymer with a block mesogenic side‐group is demonstrated. The block mesogene is an amphipathic molecule containing a hydrophobic mesogene (azotolane moiety) and hydrophilic oligooxyethylene moieties in the same unit. The block mesogene in the polymer plays a role in liquid crystalline, amphiphilic and photoresponsive properties. As expected, a film prepared from the polymer exhibits phase separation of a lamellar structure due to cooperative motion between liquid crystal assembly and nanophase separation. The morphology of the lamellae can be aligned upon irradiation of linearly polarized light. Moreover, a photochemical phase transition induced by unpolarized UV irradiation erases the surface morphology. The erased nanostructure can be recovered by annealing or irradiation of linearly polarized light, meaning that the surface morphology is rewritable via a photochemical process.

Reversible switching of the shear modulus of photoresponsive liquid-crystalline polymers.

Manipulation makes light work: The morphology and rheological properties of a liquid-crystalline system can be dynamically manipulated with UV light by attaching photoresponsive liquid-crystalline moieties to a siloxane-based polymer. Stimulation with UV light induces a conformational change in the molecule, which disrupts the liquid-crystalline mesophase (see picture), and results in a dramatic change in its rheological properties.

Photochemical Switching Behavior of Liquid Crystalline Polymer Networks Containing Azobenzene Molecules

Photoresponsive liquid crystalline polymer networks with macroscopically uniaxial molecular orientation were prepared by polymerizing mixtures of liquid crystalline mono- and diacrylates and an azobenzene compound in a homogeneous glass cell at a nematic phase. The polymer networks showed an enantiotropic phase transition from an anisotropic phase to an isotropic phase as well as high transparency. The photoisomerization of the azobenzene compound resulted in a change in a birefringence. The photochemical change in the birefriengence was investigated by using a Xe lamp and a single pulse light from a Nd:YAG laser as light sources. We observed a response time in the range of a few microseconds and a decay time in the range of a few hundred microseconds. The optical switching behavior depended on the cross-linking density of the liquid crystalline polymer networks.