Photoresponsive Actuators Research Articles

Near‐infrared light response novel shape memory actuator based on photothermal rGO‐TiO2 filler

AbstractAs an efficient method to realize photoinduced shape memory, photothermal filler has the characteristics of economy and convenience. However, the aggregation of the photothermal filler in the matrix material will reduce the material's shape memory and mechanical properties. In this work, the photothermal filler of reduced graphene oxide (rGO)‐titanium dioxide (TiO2) was prepared by the solvothermal method and then introduced into the polycaprolactone (PCL) matrices to construct a photoresponsive actuator. Because of TiO2 is uniformly loaded on the rGO surface, rGO‐TiO2 disperses well in the composites. When the GO:TiO2 ratio of photothermal filler is 1:1, the mechanical properties of PCL‐GT‐3 are the best, and the tensile strength and elongation at break are 31.8 MPa and 239.5%, respectively, and the crosslinking material under near‐infrared light has a good photothermal effect. Due to the induced difference between the in‐plane stress of the surface and the volume layer, the shape transformation can be controlled by very low energy (808 nm, 700 mW near‐infrared laser). The scheme of controlling the properties of the photoinduced shape memory material by changing only the filler type is conducive to commercial application.

Visible Light Responsive Soft Actuator Based on PVA‐DR1

AbstractThere is a growing interest in creating biomimetic actuators that can perform human‐like actions in response to external stimuli. Despite the significant advancements in soft actuators, using high‐energy UV light in photoresponsive actuators remains a great challenge. Herein, we develop a film composed of polyvinyl alcohol and photo responsive Disperse Red 1 (PVA/DR1) that actuate in response to visible light. The photoresponsive film starts to actuate in the presence of green light due to trans→cis isomerization of photoresponsive dye. The actuation response of the films was investigated by varying concentrations of DR1 dye and the intensity of green light. Based on these features, we demonstrated a four‐arm soft‐gripper that can mimic human‐hand‐like motions in response to green light. This kind of actuator may find potential applications in soft robotics and biomimetic microgrippers.

Tough, Healable, Photoresponsive Actuator Based on a Quadruple Hydrogen-Bond-Capped Slide-Ring Structure

Tough, Healable, Photoresponsive Actuator Based on a Quadruple Hydrogen-Bond-Capped Slide-Ring Structure

Facile Photoresponsive Actuators Based on Ferrocene-Doped Poly(butyl methacrylate).

This paper presents facile photoresponsive actuators comprising ferrocene as a guest chromophore and poly(butyl methacrylate) (PBMA) as a host matrix. The ferrocene-doped PBMA film exhibits mechanical expansion and contraction when a 445 nm laser is turned on and off, respectively. The photoresponsive film is attached by a commercially available acetylcellulose adhesive tape, which exhibits a bending motion that is controlled by turning the laser on and off. Thereafter, the double-layer film is employed to fabricate a table-shaped lifting machine (0.7 mg) that lifts a 10.5 mg object up and down by turning the laser on and off, respectively, and the mechanical force offered by the double-layer film is recorded. Additionally, the film is coated with gold and applied to an electric circuit that serves as a reversible photoresponsive switch. This film preparation technique is applied to other chromophores (e.g., Coumarin 343, Rhodamine 6G, Sudan Blue II, and Solvent Green 3) to independently control the motions of the films with 445, 520, and 655 nm lasers. The ferrocene-containing films also exhibit photoinduced healing from mechanical damage. Finally, the photoirradiation-accompanied morphological changes in the film are observed via small-angle X-ray scattering.

Bio-Based, Self-Healing, Recyclable, Reconfigurable Multifunctional Polymers with Both One-Way and Two-Way Shape Memory Properties

Shape memory polymers (SMPs) have attracted wide attention over the past few decades due to their fantastic applications in modern life. Nevertheless, excellent self-healing properties, recyclability, solid-state plasticity, and reversible shape-switching ability are necessary but can rarely be satisfied in one material. Herein, we report multifunctional SMPs by constructing a dynamic boronic ester bond cross-linking network using sustainable Eucommia ulmoides gum as a raw material. Thanks to the crystallization and wide melting temperature range, these kinds of SMPs have thermal-triggered one-way shape memory performance and show two-way shape memory properties, whether under constant stress or stress-free conditions. Owing to the dynamic nature of the boronic ester bond, it exhibits good self-healing properties (near 100% at 80 °C), shape reconfigurability, and chemical recyclability. In addition, by incorporating multiwalled carbon nanotubes, the formed composite is responsive to 808 nm near-infrared light. Its applications are further exploited, including photoresponsive actuators, vascular stents, and light-driven switches. This paper provides a simple way for fabricating multifunctional SMPs, and the as-prepared materials have potential applications in diverse fields, such as biomedicine, intelligent sensing, and soft robotics.

A functionalized CNT-azobenzene-PVA-based self-healing aqueous gel as a conductive photo-responsive actuator

Responsive conductive gels have gained attention owing to potential applications in flexible displays, implantable medical devices, touch panels, wearable electronic skin, sensors, soft robotics, and related areas.

A Facile Approach for 4D Microprinting of Multi‐Photoresponsive Actuators

AbstractFor microscale 4D photoresponsive actuators, light is crucial in two ways. First, the underlying additive manufacturing techniques rely on photopolymerization processes triggered by the absorption of light. Second, the absorption of light serves as the actuation stimulus. The two absorptions can be conflicting. While the microstructure requires strong absorption at the actuation wavelength(s), this absorption should not interfere with that of the manufacturing process. Herein, a simple strategy is proposed to overcome these limitations and allow for the fabrication of multi‐photoresponsive 3D microstructures that can be actuated at different wavelengths of light. Two‐photon 3D laser printing is selected as the fabrication technique and liquid crystalline (LC) elastomers as the functional materials. In a first step, 3D microstructures are fabricated using an aligned LC ink formulation. Thereafter, up to five different dyes exhibiting absorptions that extend over the entire visible regime (400–700 nm) are successfully incorporated into the LC microstructures by an exchange process enabling a programmable actuation by irradiating with the suitable wavelength. Furthermore, by combining dyes exhibiting orthogonal absorptions, wavelength‐selective actuations are demonstrated.

Biobased Composites with High Lignin Content and Excellent Mechanical Properties toward the Ingenious Photoresponsive Actuator

The fabrication of biobased smart materials from renewable biomasses is of great importance for sustainable development. Although lignin possesses photothermal conversion potential, the development of lignin-based actuators with large contraction and fast photoresponse has various hurdles. Herein, simply by blending with castor oil-derived polyamide elastomers, a lignin-based photoresponsive actuator can be obtained, which accomplishes up to 18% light-driven contraction under loading within 3 s. The crystals in polymer matrix serve as switch segments, firmly locking the stress-induced strain energy, which is swiftly released due to photothermal processes and induced a huge contraction. The composite, LP4-50, can contract and induce dynamic bending in multiple directions when irradiated locally with a near-infrared 808 nm laser. Furthermore, at standard 1 sun irradiation (100 mW/cm2), LP4-50 was successfully employed to power a thermoelectric generator. This strategy establishes the groundwork for further research into the photothermal characteristics of lignin and encourages new applications in stimulus-responsive actuators.

Understanding the Molecular Origin of the Collective Movement in a Diarylethene-based Photo-Responsive Actuator.

Remotely controlling macroscopic movement is one of the key elements to realize intelligent materials for applications ranging from sensing to robotics. Over the last few years, a number of photomechanical materials based on diarylethene derivatives have been developed. However, a detailed picture of the structural evolution within these soft actuators is often missing. In this work, an atomistic investigation uncovers how the photo‐induced molecular dynamics propagates to large‐scale motion and results in macroscopic deformation of the crystal. By correlating the intramolecular rearrangement within the photo‐responsive switching unit with the intermolecular packing, the molecular mechanism for the photomechanical phenomena is deciphered, which is fundamental for a rational development of photo‐responsive actuators.

Quantitative measurement and mechanism analysis of the high-efficiency laser propulsion of a graphene sponge.

Laser propulsion of a graphene sponge shows tremendous potential in propellant-free flight, photoresponsive actuators and micro opto-electro mechanical systems. However, the mechanism is still in dispute and the propulsion force hasn't been accurately measured, seriously hindering its development. This work develops a quantitative method to measure the propulsion force. It is found that the characteristics of the force agree qualitatively with the Knudsen force due to laser-induced thermal nonequilibrium in rarefied gas, which might be another possible mechanism of laser propulsion of a graphene sponge. Also, this kind of laser propulsion is highly efficient, stable and sustainable.

Azobenzene Based Photo-responsive Mechanical Actuator Fabricated by Intermolecular H-bond Interaction

Photo-responsive mechanical actuator is a class of stimuli-responsive materials transferring light to mechanical energy through macroscopic transformation. To fabricate photo-responsive mechanical actuator, soft polymeric materials crosslinked with functional bridging structures are desired. Supramolecular interaction is a relatively common way to fabricate crosslinked materials due to its excellent self-assembly performance. And azobenzene and derivatives are ideal candidates of photo-responsive materials because of the unique photo-induced trans-cis isomerization. Here, a new kind of crosslinked materials based on supramolecular interaction between 4,4′-dihydroxyazobenzene and chitosan is reported. Under 355 nm irradiation, the macroscopic bending of polymeric materials occurs rapidly due to the photo-isomerization of 4,4′-dihydroxyazobenzene. Meanwhile, the photo-responsive mechanical actuator can also lift weight which is up to 200 times that of the actuator itself, and convert energy from light to mechanical work efficiently. This report suggests a new kind of photo-responsive actuator based on supramolecular interaction and may be helpful to contribute a theoretical basis to the design and synthesis of photo-responsive mechanical actuator suitable for large-scale manufacturing industrialization in future.

Hexaarylbiimidazoles(HABI)-functionalized lyotropic liquid crystalline systems as visible light-responsive materials

Hexaarylbiimidazoles (HABIs) are a promising class of photoswitchable molecule that have received little attention in the literature. Among them, (2,2′-dimethoxydiphenylimidazole)-1,1′-binaphthyl (HABI1) displays unusual negative photochromism and is responsive to green light. This study investigates the potential of HABIs to serve as photo-responsive actuators controlling the structure of lyotropic liquid crystalline (LLC) materials. HABI1 with four methyl chains and HABI2 with four dodecyl chains were synthesized. Time resolved small angle X-ray scattering was used to characterize the potential disruptive effects of HABIs on the nanostructure of LLC systems. HABIs underwent rapid isomerization under irradiation, with a very slow reversion in the dark in toluene and in the LLC matrix, demonstrating excellent stability and photo-fatigue resistant. HABIs completely triggered phase transitions in the phytantriol-based materials, and HABI2 generated a greater disruption than HABI1 on the lipid packing due to the enhanced steric influence. Tuning the lipid composition yielded systems that transitioned from a “slow release” lamellar phase to a “burst release” bicontinuous cubic phase upon light irradiation. Such systems therefore may exhibit a triggered release behavior upon a short time of irradiation, showing great potential in “on demand” drug delivery.

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo-Responsive Actuators.

Arbitrary shape (re)programming is appealing for fabricating untethered shape‐morphing photo‐actuators with intricate configurations and features. We present re‐programmable light‐responsive thermoplastic actuators with arbitrary initial shapes through spray‐coating of polyethylene terephthalate (PET) with an azobenzene‐doped light‐responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami‐like folds and left‐ and right‐handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area‐specific actuation such as winding, unwinding and unfolding. By shape re‐programming, the same sample can be re‐designed and light‐actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo‐responsive actuators with highly tuneable geometries and actuation modes.

Liquid Crystal Networks on Thermoplastics: Reprogrammable Photo‐Responsive Actuators

AbstractArbitrary shape (re)programming is appealing for fabricating untethered shape‐morphing photo‐actuators with intricate configurations and features. We present re‐programmable light‐responsive thermoplastic actuators with arbitrary initial shapes through spray‐coating of polyethylene terephthalate (PET) with an azobenzene‐doped light‐responsive liquid crystal network (LCN). The initial geometry of the actuator is controlled by thermally shaping and fixing the thermoplastic PET, allowing arbitrary shapes, including origami‐like folds and left‐ and right‐handed helicity within a single sample. The thermally fixed geometries can be reversibly actuated through light exposure, with fast, reversible area‐specific actuation such as winding, unwinding and unfolding. By shape re‐programming, the same sample can be re‐designed and light‐actuated again. The strategy presented here demonstrates easy fabrication of mechanically robust, recyclable, photo‐responsive actuators with highly tuneable geometries and actuation modes.

Opposite Self-Folding Behavior of Polymeric Photoresponsive Actuators Enabled by a Molecular Approach.

The ability to obtain 3D polymeric objects by a 2D-to-3D shape-shifting method is very appealing for polymer integration with different materials, from metals in electronic devices to cells in biological studies. Such functional reshaping can be achieved through self-folding driven by a strain pattern designed into the molecular network. Among polymeric materials, liquid crystalline networks (LCNs) present an anisotropic molecular structure that can be exploited to tailor internal strain, resulting in a natural non-planar geometry when prepared in the form of flat films. In this article, we analyze the influence of different molecular parameters of the monomers on the spontaneous shape of the polymeric films and their deformation under different stimuli, such as heating or light irradiation. Modifying the alkilic chains of the crosslinkers is a simple and highly effective way to increase the temperature sensitivity of the final actuator, while modifying ester orientation on the aromatic core interestingly acts on the bending direction. Combining such effects, we have demonstrated that LCN stripes made of different monomeric mixtures originate complex non-symmetric deformation under light activation, thus opening up new applications in photonic and robotics.

Photoresponsive Soft Actuators: Photoresponsive Actuators Built from Carbon‐Based Soft Materials (Advanced Optical Materials 16/2019)

Photoresponsive Soft Actuators: Photoresponsive Actuators Built from Carbon‐Based Soft Materials (Advanced Optical Materials 16/2019)

Photoresponsive Actuators Built from Carbon‐Based Soft Materials

AbstractPhotoresponsive soft actuators with photomechanical energy conversion and flexibility have attracted significant interest in recent years owing to their unique merits of flexibility, contactless operation, and remote control, as well as their multiple technological applications ranging from bionic robotics and biomedical devices to nanomotors. Seeking efficient photoresponsive materials with high energy conversion efficiency and robust mechanical properties and identifying effective photoactuation mechanisms are of paramount significance for the development of advanced photoactuators. Due to their unique optical properties, high mechanical strength, superior electrical and thermal conductivity, good flexibility, and stability, carbon‐based materials are regarded as attractive candidates for high‐performance photoresponsive actuators. Furthermore, easy functionalization or hybridization with other functional species substantially extends the functions of these materials and widens the application scope for photoactuators. Herein, this review summarizes the recent progress of photoactuators based on various carbon‐based soft materials, including 0D, 1D, 2D, and 3D nanocarbons as well as their functional soft composites with other responsive materials. Multiple driving schemes of photoresponsive actuators including photothermal, photomechanical, photoelectronic, and photochemical effects, photoactuating architecture design, and potential technological applications of photoactuators are elucidated. Furthermore, certain future opportunities and challenges in the ever‐flourishing optical‐to‐mechanical energy conversion area are emphasized and discussed.

Thermo- and Photoresponsive Actuators with Freestanding Carbon Nitride Films.

The development of versatile actuators that convert environmental energy (heat or light, especially sunlight) into mechanical energy remains a great challenge. Herein, freestanding carbon nitride films were prepared by the physical vapor deposition method using bulk g-C3N4 powder as a starting material. The carbon nitride films exhibited controllable deformation under the stimuli of heat and light. An alarm device for high temperature and an artificial hand for grasping and releasing objects were designed. By utilizing the photothermal effect, a smart curtain that could block the UV rays and a manipulator that could perform sophisticated mechanical work were demonstrated under the direct irradiation of natural and simulated sunlight. This work exploited the potential applications of carbon nitride polymers for the conversion of solar energy to mechanical energy.

Solvent-Free Photoresponsive Artificial Muscles Rapidly Driven by Molecular Machines.

We prepared photoresponsive actuators as both hydrogels and dry gels consisting of 4-arm poly(ethylene glycol) (PEG) cross-linked by a [c2]daisy chain, which is a double-threaded [2]rotaxane dimer with α-cyclodextrin (αCD) and stilbene. The obtained gels showed fast and large deformation triggered by UV irradiation in both wet and dry states. The UV/vis spectroscopy results, NMR measurements and tensile tests on the gels revealed that the actuation is driven by photoisomerization of the stilbene unit in the [c2]daisy chain. The responsiveness of these gels depends on the molecular weight of the 4-arm PEG. These results suggest that αCD recognizes trans-stilbene prior to UV irradiation to maintain the length of the PEG chain in the polymer network and that photoisomerization allows αCD to leave the cis-stilbene moiety and move onto the PEG chain because the association constant of αCD with cis-stilbene is quite low. Thus, the sliding motion of the αCD unit shrinks the [c2]daisy chain, leading to the contraction of the gels. In both wet and dry states, these actuations are repeatable through reversible photoisomerization of the stilbene moiety using different wavelengths of UV-light irradiation and can be used to perform bending and lifting actions (for 15 times heavier weight compared to the dry gel).

(Invited) Photo Stimuli Responsive Supramolecular Actuators Constructed By Non-Covalent or Topological Crosslinkers

Various kinds of biological molecular motors, such as myosin, kinesin, and dynein, realize the conversion of energy in ATP hydrolysis into mechanical work. These mechanical motions inspired supramolecular chemist to realize polymeric materials with supramolecular materials. Two structural approaches may realize supramolecular actuators through host–guest interactions: a method with a linear main chain and one with a side chain in the polymer structure (Fig. 1).1) We have prepared photo responsive supramolecular actuators by integrating host–guest interactions on the polymer side chains (Fig. 1a). The association and dissociation of inclusion complexes as crosslinking units on the polymer side chains demonstrate contraction and expansion motions due to changes in the crosslinking density. A plate-shaped actuator bent against the incident ultraviolet (UV) light. 2) Herein we hypothesize that polymer chains crosslinked with [c2]daisy chains would realize a novel supramolecular actuator whose volume contracts upon UV light irradiation but expands upon visible (Vis) light irradiation. This contraction would bend the flat plate actuator toward the incident UV light because UV irradiation causes the shrinkage of the end-to-end distance of the [c2]daisy chain to shrink polymeric materials due to desorption of the solvent on the exposed surface (Fig. 1b). Supramolecular hydrogels containing CD-based [c2]daisy chains as crosslinkers contract and expand through photoresponsive sliding motions of the [c2]daisy chain (Fig. 1c).3) The photogenerated supramolecular artificial muscle is reminiscent of contraction and expansion motions of biological skeletal muscle. Figure 1. Supramolecular actuators using cyclodextrin derivatives. These supramolecular actuators show macroscopic contraction–expansion and flexing behaviors. References (1) Harada, A.; Takashima, Y.; Nakahata, M. Acc. Chem. Res. 2014, 47, 2128-2140. (2) Takashima, Y.; Hatanaka, S.; Otsubo, M.; Nakahata, M.; Kakuta, T.: Hashidzume, A.; Yamaguchi, H.; Harada, A. Nat. Commun. 2012, 3, 1270. (3) Iwaso, K.; Takashima, Y.; Harada, A. Nat. Chem. 2016, 8 , 625–632. (4) Takashima, Y.; Harada, A. J. Incl. Phenom. Macrocycl. Chem. 2017, 87, 313-330. Figure 1