Graphene‐Based Bimorph Actuators with Dual‐Response and Large‐Deformation by a Simple Method

There is a high demand for the design of high‐performance soft actuators with multi‐stimuli response and easy fabrication. Here, soft bimorph actuators consisting of graphene and polypropylene are fabricated by the drop‐coating of graphene film and subsequent adhesion of polypropylene on the graphene film. The fabrication method is simple, fast, and scalable, and this bimorph actuator exhibits optically and electrically induced actuation with large and reversible deformation (angle change > 100°), fast response (≈8 s), and low driving voltage (≤7 V). The remarkable actuation performance is mainly attributed to the thermally induced expansion of the polypropylene film, bimorph structure, and the energy conversion property of the graphene. Because of the dual‐responsiveness and large‐deformation, this actuator can be used to construct diversely biomimetic devices with smart mechanical output. As an example, an artificial flower composed of four pieces of the actuator is fabricated to show optically and electrically driven blooming. These results open the way for using a simple method for the construction of soft actuators and smart devices toward practical biomimetic applications.     

Synthesis,characterization and actuation behavior of polyaniline‐coated electroactive paper actuators

This investigation deals with the synthesis, characterization and actuation behavior of conductive polyaniline‐coated electroactive paper actuators. The actuator is made by electrochemical deposition of conductive polyaniline on a cellulose paper. The aim of the investigation was to improve the bending displacement of electroactive paper actuators. The displacement outputs of the actuators show that a trilayer is better than a bilayer configuration. The nature of the dopant ion used in the electro‐generation affects the performance. A change in humidity plays a vital role in actuation performance of the actuators. Comparing the performance of electroactive paper actuators with and without a conductive polyaniline coating, the coating improves the displacement output threefold. Finally, the actuation principle mechanism is addressed. Copyright © 2007 Society of Chemical Industry     

Electromechanical properties of CaZrO3 modified (K,Na)NbO3‐based lead‐free piezoceramics under uniaxial stress conditions

Piezoelectric actuators are typically preloaded with a modest mechanical compressive stress during actuation to reduce cracking and allow for operation in the dynamic range. In addition, actuators are required to carry out mechanical work during operation, resulting in a nonlinear relationship between stress and actuation voltage. In fact, mechanical loading can significantly impact the electromechanical performance of lead‐free piezoelectrics. Herein, we report the dependence of electromechanical properties of CaZrO₃ modified (K,Na)NbO₃‐based lead‐free piezoceramics on uniaxial compressive stress, comparing to their lead‐based counterparts. It is demonstrated that increased non‐180° domain switching enhances the strain output at a moderate stress of approximately ?50 MPa from room temperature to 150°C. Larger uniaxial stress, however, is found to suppress ferroelectric domain switching, resulting in the continuous strain and polarization decrease.     

New ionic polymer–metal composite actuators based on PVDF/PSSA/PVP polymer blend membrane

Ionic polymer–metal composite (IPMC) actuators that display continuously large actuation displacements without back relaxation and with large blocking force at low direct current (DC) voltages are used as biomimetic sensors, actuators and biomedical devices. This article reports the preparation and actuation performance of new IPMC actuators based on the polyvinylidene fluoride (PVDF)/polystyrene sulfonic acid (PSSA)/polyvinyl pyrrolidone (PVP) polymer blend membrane, which requires low voltage DC. The performance results of the proposed IPMC actuators are compared with Nafion‐based IPMC actuators. In the blend membrane, PVDF is the hydrophobic polymer, PSSA is the polyelectrolyte, and PVP is the hydrophilic basic polymer. The proposed IPMC actuators based on the PVDF/PSSA/PVP blend membrane of polymer mixture ratios of 60/15/25 and 50/25/25 gave higher actuation displacement and higher blocking force at low DC voltages than the Nafion‐based IPMC actuator. POLYM. ENG. SCI., 2011. © 2011 Society of Plastics Engineers     

Human‐Iris‐Like Aperture and Sphincter Muscle Comprising Hyperelastic Composite Hydrogels Containing Graphene Oxide

Soft hydrogels are extensively studied for developing human‐body‐mimicking actuators because of their stimuli‐responsive volume change and elasticity. Mimicking a human eye with hydrogels is very challenging because both the large variation in the volume and the high modulus of the gels should be concurrently achieved. In the human eye, adjusting the iris for controlling the focal point and light transmittance is achieved by the contraction of the sphincter muscle. In this work, a hyperelastic poly(N‐isopropylacrylamide) containing graphene oxide (PNIPAm/GO) composite hydrogels, which exhibits a thermo‐responsive volume phase transition is developed. The fact that the inner hole size for center‐cut hydrogels can increase or decrease during heating depending on the geometry of the hydrogels is revealed. Based on these findings, human‐iris‐like actuators capable of controlling the shape of a polydimethylsiloxane (PDMS) lens for adjusting magnification of an object is developed. When heated, the hyperelastic hydrogels act like the sphincter muscle in the eye, inducing the curvature change of the attached PDMS lens. Thus, hyperelastic hydrogels of large variation can provide an efficient platform to fabricate various soft actuation systems.     

Maximum actuation strain for dissipative dielectric elastomers with simultaneous effect of prestretch and temperature

A dielectric elastomer can generate giant deformation by the voltage actuation, but the deformation is often hindered by the electromechanical instability and “snap‐through deformation,” which may lead to electrical breakdown. In this study, for the first time, the mathematical model is established for dissipative dielectric elastomers in the dynamic model with simultaneous effect of prestretch and temperature in order to achieve maximum actuation strain. The deformation of the dissipative dielectric elastomer: VHB 4905/4910 is investigated for the two simple actuation methods: constant and ramping voltage actuation, respectively. The best combined conditions of voltage and prestretch to obtain a large deformation at different operating temperatures are studied in detail. Under the best combined conditions, the influences of three factors: voltage, prestretch, and temperature on the maximum actuation strain are analyzed. This study should offer a great help in the design of dielectric elastomer actuators, and give the guidance to the accomplishment of the large deformation of dissipative dielectric elastomer actuators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45850.     

Thermomechanical effects in the torsional actuation of twisted nylon 6 fiber

Thermally induced torsional and tensile actuators based on twisted polymeric fibers have opened new opportunities for the application of artificial muscles. These newly developed actuators show significant torsional deformations when subjected to temperature changes, and this torsional actuation is the defining mechanism for tensile actuation of twisted and coiled fibers. To date it has been found that these actuators require multiple heat/cool cycles (referred to as “training” cycles) prior to obtaining a fully reversible actuation response. Herein, the effect of annealing conditions applied to twisted nylon 6 monofilament is investigated and it is shown that annealing at 200 °C eliminates the need for the training cycles. Furthermore, the effect of an applied external torque on the torsional actuation is also investigated and torsional creep is shown to be affected by the temperature and load. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45529.     

Improved electromechanical response in acrylic rubber by different carbon‐based fillers

Dielectric elastomers are materials often utilized for the fabrication of electroactive actuators. Acrylic rubber (ACM) is very widely used in dielectric elastomer actuators (DEAs). However, its overall good performance is limited by the high operating electric field required. In the present work, we compare the effect of different types of conventionally used carbon black (CB) as well as other carbon‐based fillers on the dielectric and actuation properties of ACM in order to show that performance of DEAs can be improved by the development of ACM composites. Indeed, addition of CB, carbon nanotubes (CNTs), and synthetic graphite leads to an increase in the relative dielectric permittivity of elastomeric material. Moreover, incorporation of nanodiamonds results in reduction of dielectric losses. Finally, actuation stress is remarkably improved by CNTs and different grades of CB. POLYM. ENG. SCI., 58:395–404, 2018. © 2017 Society of Plastics Engineers     

Ionic polymer‐metal composites made from radiation grafted FEP‐g‐styrene‐SO3H membranes

Ionic polymer‐metal composites have been made from radiation grafted fluorinated ethylene propylene (FEP) membranes. Membranes have been synthesized by grafting of styrene on FEP films followed by sulfonation. These membranes were then used to fabricate IPMCs. Chemical plating of silver has been done to form the microelectrodes. Influence of degree of grafting on actuation, surface resistance, and tensile properties of the IPMC have been evaluated. It has been observed that on increasing the degree of grafting surface resistance, tensile strength, and elongation of IPMC decrease while degree of actuation and modulus increase. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Effect of poly(ethylene oxide)‐ poly(ethylene glycol) addition on actuation behavior of cellulose electroactive paper

This article reports the influence of poly(ethylene oxide)‐ poly(ethylene glycol) (PEO‐PEG) addition on its actuation behavior of cellulose electroactive paper. The actuator showed its maximum bending displacement of 5.0 mm with very low electrical power consumption (7 mW/mm) at an ambient condition. Increased displacement output and decreased electrical power consumption of the actuator might be due to the improved polymer chain flexibility and ion mobility. The ion migration effect might play a more important role in actuation principle. Present investigation reveals that cellulose/PEO‐PEG‐based EAPap actuators are suitable to construct an actuator working at normal ambient condition. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Near‐Infrared Light Triggered Soft Actuators in Aqueous Media Prepared from Shape‐Memory Polymer Composites

Light triggered soft actuator in aqueous media has applications in operating underwater objects, creating liquid flow, and adjusting reaction velocity, etc. Here, composites prepared from commercial materials, poly[ethylene‐ran‐(vinyl acetate)] (EVA) and aniline black (AB), are reported as one cost efficient material for preparing such actuator, where EVA and AB work respectively as shape‐memory polymer matrix and near‐infrared light triggered photothermal filler. Upon irradiation, the temperature of the composites increases greatly with light power density and AB content. Light‐induced shape‐memory effect (SME) with recovery ratio >98%, temperature‐memory effect (TME), and reversible bidirectional shape‐memory effect (rbSME) of the prepared composites in air are realized. Higher light power density is required to trigger the shape recovery in aqueous media, while good SME, TME, and rbSME are also achieved. Releasing device and gripper are used to indicate the feasibility of the composites as light triggered soft underwater actuators.

     

Significantly improving electro‐activated shape recovery performance of shape memory nanocomposite by self‐assembled carbon nanofiber and hexagonal boron nitride

This study presents two effective approaches to significantly improve the electro‐thermal properties and electro‐activated shape recovery performance of shape memory polymer (SMP) nanocomposites that are incorporated with carbon nanofibers (CNFs) and hexagonal boron nitrides (h‐BNs), and show Joule heating triggered shape recovery. CNFs were self‐assembled and deposited into buckypaper form to significantly improve the electrical properties of SMP and achieve the shape memory effect induced by electricity. The h‐BNs were either blended into or self‐assembled onto CNF buckypaper to significantly improve the thermally conductive properties and electro‐thermal performance of SMPs. Furthermore, the shape recovery behavior and temperature profile during the electrical actuation of the SMP nanocomposites were monitored and characterized. It was found that a unique synergistic effect of CNFs and h‐BNs was presented to facilitate the heat transfer and accelerate the electro‐activated shape recovery behavior of the SMP nanocomposites. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40506.     

Surface grafting of carbon fibers with artificial silver‐nanoparticle‐decorated graphene oxide for high‐speed electrical actuation of shape‐memory polymers

Poor heat conduction in the interface between the carbon fiber and polymer matrix is a problem in the actuation of shape‐memory polymer (SMP) composites by Joule heating. In this study, we investigated the effectiveness of grafting silver‐nanoparticle‐decorated graphene oxide (GO) onto carbon fibers to improve the electrothermal properties and Joule‐heating‐activated shape recovery of SMP composites. Self‐assembled GO was grafted onto carbon fibers to enhance the bonding of the carbon fibers with the polymeric matrix via van der Waal's forces and covalent crosslinking, respectively. Silver nanoparticles were further self‐assembled and deposited to decorate the GO assembly, which was used to decrease the thermal dissimilarity and facilitate heat transfer from the carbon fiber to the polymer matrix. The carbon fiber was incorporated with SMP to achieve the shape recovery induced by Joule heating. We found that the silver‐nanoparticle‐decorated GO helped us achieve a more uniform temperature distribution in the SMP composites compared to those without decoration. Furthermore, the shape‐recovery behavior and temperature profile during the Joule heating of the SMP composites were characterized and compared. A unique synergistic effect of the carbon fibers and silver‐nanoparticle‐decorated GO was achieved to enhance the heat transfer and a higher speed of actuation. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41673.     

A temperature-responsive dual network hydrogel for reversible smart actuator

Nowadays, soft actuators have received extensive attention in many application fields, among which hydrogels have become an important choice for constructing soft actuators due to their unique properties. However, the actuating behaviors of hydrogel-based actuators are usually monotonous due to their unchangeable shapes and structures. Herein, we report a temperature-responsive hydrogel actuator with a bilayer structure. Based on the dual network structure (polyvinyl alcohol/poly acrylamide and polyvinyl alcohol/poly (N-isopropylacrylamide), the actuators can realize the reinforcement compared with the single network. Because of the intrinsic lower critical solution temperature of poly (N-isopropylacrylamide, both sides of actuators have different swelling rates, enabling them to achieve the thermal-responsive actuation and shape programming. Therefore, this work is promising to provide a new strategy for designing temperature switches and thermally driven soft robots.     

Graphene/poly(styrene‐b‐isoprene‐b‐styrene) nanocomposite optical actuators

This article presents an optomechanical actuator, which is driven by infra red (IR) radiation. The actuator is a nanocomposite‐containing graphene platelets embedded in poly(styrene‐b‐isoprene‐b‐styrene) (SIS) matrix. 0.1 mm thick free‐standing nanocomposite films are fabricated by a simple process of solvent casting. We demonstrate that graphene/SIS nanocomposite contracts on irradiation with IR radiation under strained conditions, whereas expansion behavior was exhibited by them when no prestrain is applied. A maximum photomechanical stress of 28.34 kPa and strain upto 3.1% was obtained for these nanocomposite actuators. We have also studied the mechanical characteristics and thermal degradation of these nanocomposite actuators. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 130: 3902–3908, 2013     

Mechanical,dielectric, and electromechanical properties of silicone dielectric elastomer actuators

Silicone elastomer actuators were investigated to develop a simple and industrially scalable product with improved mechanical properties, such as a low modulus, high tearing strength, and good resilience, and enhanced electromechanical actuation properties. Silicone elastomers were fabricated via a hydrosilylation addition reaction with a vinyl‐end‐functionalized poly(dimethyl siloxane) (V), a multivinyl‐functionalized silicone resin, and a crosslinker in the presence of a platinum catalyst. For the larger electromechanical actuation response, the silicone dielectric elastomer actuator had to have a larger molecular weight of poly(dimethyl siloxane), a smaller hardener content, and a resin‐free composition. However, the silicone elastomer actuators needed to include a small amount of resin to improve the tearing strength. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2014 , 131, 40030.     

Electric Fatigue of Lead‐Free Piezoelectric Materials

A considerable body of knowledge now exists from studies involving the development of lead‐free piezoelectric ceramics and a number of high potential alternatives to current lead‐based materials have been identified. Stability under cyclic electric fields is an important property of piezoelectric materials. Here, we review the research to date which shows that fatigue under cyclic electrical loading is prevalent in many lead‐free piezoelectric ceramic compositions. However, the variety of compositions and mechanisms for piezoelectric behavior in these materials corresponds to significant variances in the nature of fatigue degradation and the likely mechanisms thereof, which do not directly parallel those of well‐studied lead‐based materials. In particular, the use of field‐induced phase changes as an actuation mechanism provides distinctive fatigue behaviors. Particular attention is given to fatigue of ferroelectric and relaxor (ergodic and nonergodic) structures and their dependence upon temperature and electric field and the potential design of materials with high fatigue resistance.     

Linear Actuation Using Milligram Quantities of CL‐20 and TAGDNAT

There are numerous applications for small‐scale actuation utilizing pyrotechnics and explosives. In certain applications, especially when multiple actuation strokes are needed, or actuator reuse is required, it is desirable to have all gaseous combustion products with no condensed residue in the actuator cylinder. Toward this goal, we have performed experiments on utilizing milligram quantities of high explosives to drive a millimeter‐diameter actuator with a stroke of 30 mm. Calculations were performed to select proper material quantities to provide 0.5 J of actuation energy. This was performed utilizing the thermochemical code Cheetah to calculate the impetus for numerous propellants and to select quantities based on estimated efficiencies of these propellants at small scales. Milligram quantities of propellants were loaded into a small‐scale actuator and ignited with an ignition increment and hot wire ignition. Actuator combustion chamber pressure was monitored with a pressure transducer and actuator stroke was monitored using a laser displacement meter. Total actuation energy was determined by calculating the kinetic energy of reaction mass motion against gravity. Of the materials utilized, the best performance was obtained with a mixture of 2,4,6,8,10,12‐hexanitro‐2,4,6,8,10,12‐hexaazaisowurtzitane (CL‐20) and bis‐triaminoguanidinium(3,3′dinitroazotriazolate) (TAGDNAT).     

3D-Printed Poly(acrylic acid–vinylimidazole) Ionic Polymer Metal Composite Actuators

Ionic polymer–metal composites (IPMC)—constructed using an ionic polymer sandwiched between metal electrodes—have shown great potential for the fabrication of soft actuators. IPMC architectures have many advantages including low actuation voltage, fast response, basic control, and relatively light weight. Poly(acrylic acid) (PAA)-based ion exchange membranes are of particular interest for IPMC devices due to their large ion exchange capacity and ease of preparation; however, they suffer from relatively weak mechanical strength. Here, PAA-based soft actuators are synthesized with enhanced mechanical properties and proton conductivity through the incorporation of hydrogen bonding interactions with imidazolium groups via copolymerization with 1-vinylimidazole. In addition to examining the impact of composition on physiochemical (swelling, glass transition, decomposition, Young's modulus, etc.) and electrochemical (specific capacitance) properties, an additive manufacturing process, digital light projection (DLP), is utilized to fabricate complex geometries demonstrating the potential for the fabrication of IPMC devices with complex actuation modalities. Planar DLP 3D-printed IPMC actuators of varied polymer compositions are fabricated with activated carbon and copper electrodes, and their actuation performance is evaluated in air, where large bending deformation is observed (14°–37°).