Smart microstructured materials enable functions such as actuation, detection, transportation, and sensing with potential applications ranging from robotics and photonics to biomedical devices. Of ...the many materials systems, liquid crystal polymer networks (LCN) are fascinating owing to their ability to exhibit reversible macroscopic deformation driven by a molecular order–disorder phase transition. LCN have been increasingly explored for their utility in the design and fabrication of smart actuating devices capable of complex shape changes or motions upon external stimulation of humidity, heat, light, and other stimuli, and recent studies in this field show that their actuation complexity can be enriched and actuation performance enhanced by having some sort of microstructures. Herein, the recent progress in microstructured actuation of LCN materials with substructures in scale ranging from micrometer to millimeter is reported, placing the emphasis on the main approaches to generating a microstructure in LCN, which include patterned LC director fields, patterned chain crosslinking in LCN with uniaxial orientation of mesogens, 3D/4D printing, and replica molding. The potential applications in microstructured 3D actuators and devices as well as functional LCN surfaces are also highlighted, with an outlook on important issues and future trends in smart microstructured LCN materials and actuators.
Reported is the recent research progress in developing dynamic microstructured materials based on liquid crystal polymers that are responsive to heat or light through an order–disorder phase transition. Their design, fabrication, function, actuation, and potential applications are discussed.
A strip of a liquid crystal elastomer doped with a near‐infrared dye with one side crosslinked monodomain and the other crosslinked polydomain along the thickness behaves like a multifunctional ...photoactuator without the need for a support. A flat strip with two ends fixed on substrate surface forms a moving bump under laser scanning, which can be used as light‐fueled conveyor to transport an object. Cutting off and laser scanning the bump with two free ends makes a soft and flexible millimeter‐scale crawler that can not only move straight and climb an inclined surface, but also undergo light‐guided turning to right or left as a result of combined out‐of‐plane and in‐plane actuation. Based on the self‐shadowing mechanism, with one end of the strip fixed on substrate surface, it can execute a variety of autonomous arm‐like movements under constant laser illumination, such as bending–unbending and twisting, depending on the laser incident angles with respect to the strip actuator.
Jack of all trades: A photocrosslinkable liquid‐crystal polymer doped with a near‐infrared (NIR) dye acts as a multitasking soft actuator. It can be made to act as light‐driven walking belt for object transportation, a micro‐crawler capable of turning in its movement, and a self‐sustained oscillating arm.
It is very challenging to make materials capable of autonomous oscillation known in many living systems (such as the heartbeat). Herein, we describe an approach to creating a thermo-mechano-thermal ...feedback loop for thermal phase transition-based polymer actuators, which leads to hour-long, autonomous motion on a substrate surface of constant temperature. We investigated the variables that determine the amplitude and period of the motion, and demonstrated exemplary physical work powered by direct thermomechanical energy conversion. Such continuous motion of a solid polymer driven by thermal energy without the need for temperature up/down switching is unprecedented, and the validated feedback loop can be implemented into other thermal phase transition-based polymer actuators.
Display omitted
•Hydrolytic resistance of PLA enhanced by poly(dodecafluorheptyl methylacrylate) (PFA).•The architecture of PLA formed by different distribution of PFA.•The diffusion of water and ...hydrolytic products controlled by the architecture of materials.•Hydrolytic mechanism affected by the diffusion of small molecules.
Poly(lactic acid) (PLA) coated with poly(dodecafluorheptyl methylacrylate) (PFA), namely PLA-coat-PFA, and PLA blended with PFA, namely PLA-blend-PFA, together with neat PLA were subjected in 40°C water for 100days to investigate the hydrolytic behavior of the materials with different architectures. The water diffusion rate and hydrolytic behavior were studied by means of water absorption test, morphology observation, monitor of mass loss, pH measurement, thermal analysis and molecular weight determination. The results show that (1) the water permeation in PLA can be hindered by coating with PFA, while water absorption can be enhanced by blending with PFA because the gaps between PLA and PFA, resulting from poor interaction between the two phases, reduce the penetration depth; (2) the neat PLA and PLA-coat-PFA undergo heterogeneous degradation while PLA-blend-PFA behaves as homogeneous degradation, and the degradation rate follows the order: PLA>PLA-blend-PFA>PLA-coat-PFA; (3) coating and blending PFA with PLA can both delay the hydrolytic degradation of PLA by hindering water permeation and decreasing the autocatalysis of the hydrolytic products, respectively.
It is very challenging to make materials capable of autonomous oscillation known in many living systems (such as the heartbeat). Herein, we describe an approach to creating a thermo-mechano-thermal ...feedback loop for thermal phase transition-based polymer actuators, which leads to hour-long, autonomous motion on a substrate surface of constant temperature. We investigated the variables that determine the amplitude and period of the motion, and demonstrated exemplary physical work powered by direct thermomechanical energy conversion. Such continuous motion of a solid polymer driven by thermal energy without the need for temperature up/down switching is unprecedented, and the validated feedback loop can be implemented into other thermal phase transition-based polymer actuators.
A thermo-mechano-thermal feedback loop allows solid polymer actuators to undergo hour-long, autonomous motion on a substrate surface of constant temperature.
A thermo-mechano-thermal feedback loop allows solid polymer actuators to undergo hour-long, autonomous motion on a substrate surface of constant temperature.
It is very challenging to make materials ...capable of autonomous oscillation known in many living systems (such as the heartbeat). Herein, we describe an approach to creating a thermo-mechano-thermal feedback loop for thermal phase transition-based polymer actuators, which leads to hour-long, autonomous motion on a substrate surface of constant temperature. We investigated the variables that determine the amplitude and period of the motion, and demonstrated exemplary physical work powered by direct thermomechanical energy conversion. Such continuous motion of a solid polymer driven by thermal energy without the need for temperature up/down switching is unprecedented, and the validated feedback loop can be implemented into other thermal phase transition-based polymer actuators.
A strip of a liquid crystal elastomer doped with a near‐infrared dye with one side crosslinked monodomain and the other crosslinked polydomain along the thickness behaves like a multifunctional ...photoactuator without the need for a support. A flat strip with two ends fixed on substrate surface forms a moving bump under laser scanning, which can be used as light‐fueled conveyor to transport an object. Cutting off and laser scanning the bump with two free ends makes a soft and flexible millimeter‐scale crawler that can not only move straight and climb an inclined surface, but also undergo light‐guided turning to right or left as a result of combined out‐of‐plane and in‐plane actuation. Based on the self‐shadowing mechanism, with one end of the strip fixed on substrate surface, it can execute a variety of autonomous arm‐like movements under constant laser illumination, such as bending–unbending and twisting, depending on the laser incident angles with respect to the strip actuator.
Gymnastik für Flüssigkristalle: Ein durch Lichteinwirkung vernetzbares Flüssigkristallpolymer, das mit einem Nahinfrarot(NIR)‐Farbstoff dotiert ist, wirkt als weicher Aktor mit mehreren Funktionen. Es kann als lichtgetriebenes Förderband Objekte transportieren, als Mikroläufer Drehungen ausführen und als oszillierender Arm selbständig winken.
Photoresponsive actuators based on semicrystalline poly(ethylene‐co‐vinyl acetate) (EVA) loaded with small amounts of gold nanoparticles (AuNPs) are described. Upon absorption of light (532 nm), the ...heat released by the AuNPs raises the temperature in the irradiated region to Tlight to melt crystallites with lower melting temperatures (Tm<Tlight), resulting in a contraction force on the sample sustained by the crystalline skeleton domains with Tm>Tlight . Once the light is turned off, the recrystallization of oriented chains in the actuation domains upon cooling gives rise to an expansion force. We show that the photoinduced contraction force, Tlight , and the speed for reaching Tlight can readily be adjusted, which makes EVA/AuNP a robust, fast optical actuation system tunable in both speed and magnitude. The material design can easily be extended to other temperature‐memory semicrystalline polymers in combination with various light‐absorbing and heat‐generating additives.
In good shape: A semicrystalline poly(ethylene‐co‐vinyl acetate) (EVA)/gold nanoparticle (AuNP) nanocomposite can be used as an optical actuator. Both the magnitude and the speed of actuation can be tuned by adjusting the light intensity, AuNP content, specimen thickness, and elongation degree.
The nitrides and carbides of transition metals are highly favored due to their excellent physical and chemical properties, among which MXene is a hot research topic for microwave absorption. Herein, ...the controlled preparation of 3D Mo2TiC2Tx‐based microspheres toward microwave absorption is reported for the first time. With the merits of the performances of both reduced graphite oxide (RGO) and MXene sufficiently considered, the influence of carbonization temperature on the internal crystal structure and the effective microwave‐material interaction surface of the prepared Mo2TiC2Tx/RGO is systematically investigated. The structure–activity relationships relating the apparent morphology and crystal structure to the microwave absorption performance are deeply explored, and the wave absorption mechanism is put forward as well. The results show that the Mo2TiC2Tx/RGO‐700 product obtained after heating treatment at 700 °C exhibits excellent microwave absorption performance, with the RLmin being up to −55.1 dB@2.1 mm@13.8 GHz, and the corresponding effective absorption bandwidth covering 5.7 GHz. The outstanding microwave absorption characteristics are attributed to the appropriate impedance matching, high specific surface area, rich intrinsic defects, desirable conductivity, and strong multipolarization capabilities. This work enriches the types of MXene‐based composite absorbers and provides a new strategy for controlled preparation of high‐performance 3D composite absorbers.
The 3D Mo2TiC2Tx‐based microspheres are first constructed. Mo2TiC2Tx/RGO with wrinkled morphology are first applied to the microwave absorption field. The effects of carbonization temperature on its internal crystal structure and intrinsic defects are systematically investigated, and the structure–activity relationships are deeply explored. The RLmin exceeds −55.1 dB and effective absorption bandwidth covers 5.7 GHz at 15% filler loading.
A porous liquid‐crystalline network (LCN), prepared by using a template method, was found to exhibit peculiar actuation functions. The creation of porosity makes the initially hydrophobic LCN behave ...like a hydrogel, capable of absorbing a large volume of water (up to ten times the sample size of LCN). When the amount of absorbed water is relatively small (about 100 % swelling ratio), the porous LCN displays anisotropic swelling in water and, in the same time, the retained uniaxial alignment of mesogens ensures a thermally induced shape change associated with a LC‐isotropic phase transition. Combining the characteristic actuation mechanisms of LCN (order–disorder transition of mesogens) and hydrogel (water absorption), such porous LCNs can be explored for versatile stimuli‐triggered shape transformations. Moreover, the porosity enables loading/removal/reloading of functional fillers such as ionic liquids, photothermal dyes and fluorophores, which imparts the porous LCN actuator with reconfigurable functions such as ionic conductivity, light‐driven locomotion, and emissive color.
A porous liquid‐crystalline network can swell in water for actuation through both water absorption and order–disorder phase transition, and be loaded with functional fillers to display reconfigurable functions.
PDF
