Dramatic Improvement in Ionic Conductivity and Water Desalination Efficiency of SGO Composite Membranes

Energy efficient membranes of SGO (Sulfonated Graphene Oxide) into SPES (Sulfonated Polyethersulfone) matrix have been prepared containing different weight content of SGO. Proton conductivity and water retention capacity of membranes increases by increasing SGO while degree of swelling decreases. TEM micrograph shows the uniform distribution of SGO throughout the membrane. SGO-5 membrane shows the maximum proton conductivity (5.8 x 10^?2 S/cm), which is almost double to the SPES with higher stability. SGO-5 membrane shows 4.73 mole.m^?2h^?1 ionic flux, 0.98 kWhkg^?1 power consumption and 93.1% current-efficiency for salt removal, which are 62% and 15.2% higher, respectively, while 16% lower power consumption is observed as compared to SPES.     

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     

Charge Dynamics and Bending Actuation in Aquivion Membrane Swelled with Ionic Liquids

The actuation strain and speed of ionic electroactive polymer (EAP) actuators are mainly determined by the charge transport through the actuators and excess ion storage near the electrodes. We employ a recently developed theory on ion transport and storage to investigate the charge dynamics of short side chain Aquivion^® (Hyflon^®) membranes with different uptakes of ionic liquid (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMI-Tf). The results reveal the existence of a critical uptake of ionic liquids above which the membrane exhibits a high ionic conductivity (σ > 5 × 10⁻² mS/cm). Especially, we investigate the charge dynamics under voltages which are in the range for practical device operation (∼1 V and higher). The results show that the ionic conductivity, ionic mobility, and mobile ion concentration do not change with the applied voltage below 1 V (and for σ below 4 V). The results also show that bending actuation of the Aquivion membrane with 40wt% EMI-Tf is much larger than that of Nafion, indicating that the shorter flexible side chains improve the electromechanical coupling between the excess ions and the membrane backbones, while not affecting the actuation speed.     

Carbon nanotube sheet electrodes for anisotropic actuation of dielectric elastomers

The performance of dielectric electroactive polymer (D-EAP) based actuators depends critically on the electrode characteristics. Among the most challenging issues in the application of D-EAPs is the device-level complexity in producing sufficient directional actuation at acceptably low electric fields. In this work, a simple carbon nanotube (CNT) based electrode for D-EAP actuators is demonstrated that vastly improves directional strain response originating from the mechanical anisotropy of the electrode material. In this novel approach, highly aligned carbon nanotube (CNT) sheet electrodes are applied on acrylate adhesive films show high directed linear actuation strain of greater than 40% at a relatively low electric field (100 V μm⁻¹). The fiber-oriented CNT sheet applied around the D-EAP film, exhibits strong interaction between CNT fibers in the electrode and the D-EAP film to produce a robust conductive-nanolayer at the interface, on actuation cycling. The design paradigm provides a great potential for the fabrication of soft linear actuators.     

High electromechanical reponses of ultra-high-density aligned nano-porous microwave exfoliated graphite oxide/polymer nano-composites ionic actuators

High elastic energy density and high-efficiency ionic electromechanical actuators were prepared from aligned activated microwave exfoliated graphite oxide (A-aMEGO)/polymer nano-composites, and the electromechanical performance was characterized. The elastic modulus and elastic energy density of the ionic actuators can be tuned over a wide range by varying the polymer (poly (vinylidene fluoride/chlorotrifluoroethylene) [P(VDF-CTFE)]) concentration in the nano-composite actuators. The A-aMEGO/P(VDF-CTFE) nano-composite actuators with 35 wt.% of polymer content exhibit an elastic energy density higher than 5 J/cm³ and an electromechanical conversion efficiency higher than 3.5%, induced under 4 V. The results show the promise of high-density highly aligned graphene electrodes for high-performance ionic electromechanical transduction devices.     

Morphology- and ion size-induced actuation of carbon nanotube architectures

ABSTRACT

Future adaptive applications require lightweight and stiff materials with high active strain but low energy consumption. A suitable combination of these properties is offered by carbon nanotube-based actuators. Papers made of carbon nanotubes (CNTs) are charged within an electrolyte, which results in an electrical field forming a double-layer of ions at their surfaces and a deflection of the papers can be detected. Until now, there is no generally accepted theory for the actuation mechanism. This study focuses on the actuation mechanism of CNT papers, which represent architectures of randomly oriented CNTs. The samples are tested electrochemically in an in-plane set-up to detect the free strain. The elastic modulus of the CNT papers is analyzed in a tensile test facility. The influence of various ion sizes of water-based electrolytes is investigated.

During the tests, four parameters that have a significant influence on the mechanical performance of CNT papers were identified: the test conditions, the electrical charging, the microstructure and the ion size. All of these influencing factors point to the mechanically weak inter-tube linking at which the actuation seems to take place. Quadratic voltage-strain correlation suggests a combination of electrostatic and volumetric effects as the possible reason for CNT paper actuation.

Abbreviations: CNT: carbon nanotubes; CV: cyclic voltammetry; CVD: chemical vapor deposition; HiPCO: high pressure carbon monoxide; IL: ionic liquid; MWCNT: multi-walled carbon nanotube; MW: multi-walled; NHE: normal hydrogen electrode; PDMS: polydimethylsiloxane; PMMA: polymethylmethacrylate; PPy: polypyrrole; PVDF: polyvinylidenefluoride; SCE: saturated calomel electrode; SWCNT: single-walled carbon nanotube; SW: single-walled; 1M: one molar concentration     

Hygroresponsive Torsional Yarns and Actuators Based on Cascade Amplification of the Deformation

Fiber-based hygroresponsive torsional actuators provide desirable merits, such as light weight and shapeability, for developing smart systems to harvest energy from moisture which is a ubiquitous natural resource. A key challenge in this development is to realize moisture-triggered actuation combining large actuation and rapid responses. Here, a multiscale design strategy is explored to create high-performance hygroresponsive torsional actuators consisting of chitosan and multiwalled carbon nanotubes (MWCNTs). The superior actuation performance arises from the synergism of contributing factors at different scales, including 1) MWNCTs accelerate the water transport in primary twisted fibers (PTFs), fostering the rotation of PTFs upon moisture stimuli; 2) in situ-formed hierarchically-assembled twists realize cascade amplification of moisture-triggered actuation. Specifically, PTFs are self-twisted to generate secondary helical yarns, that are subsequently over-twisted to yield tertiary coiled yarn. The resultant yarn actuator can reach a maximum rotation speed of 11 400 rpm in 5 s, output gravitational potential energy of 2.4 J kg⁻¹ and gravitational potential power of 0.053 W kg⁻¹ during contraction. This work represents the first design of fiber-based actuators by virtue of moisture-triggered in situ formation of yarns. The established principles of multiscale design will enable high-performance fiber-based hygroresponsive actuators toward advanced intelligent textile and soft robotics.     

Carboxylated PIM-1 incorporating sulfonated graphene oxide effectively improves the ion transport properties of the membrane

This study explores the ion transport properties of self-microporous polymers by introducing a novel combination of carboxylated PIM-1 with sulfonated graphene oxide (SGO) to fabricate membranes. The resulting membranes exhibit enhanced structural stability, hydrophilicity, and ion exchange capacity (IEC) compared with the original carboxylated PIM-1 (CPIM-1), while preserving the subnanoporous structure. However, it was observed that excessive SGO loading leads to a detrimental “blocking effect” that compromises various membrane properties. Through electrically driven ion transport tests in a 0.01 M NaCl solution, it is demonstrated that a moderate amount of SGO effectively enhances membrane conductivity from 46.96 μS m⁻¹ (for carboxylated PIM-1 membranes without SGO) to 56.55 μS m⁻¹. Additionally, the membranes exhibit selective sieving of cations and anions. The presence of small-sized ion channels and the electrostatic repulsion generated by the abundant carboxyl and sulfonic acid groups significantly hinder Cl⁻ transport. Consequently, the Na⁺/Cl⁻ migration ratio (t₊/t₋) reaches 98 at a concentration ratio of 10:1 on both sides of the membrane, surpassing the value of 3.74 observed for the pure CPIM-1 membrane. This investigation provides valuable insights for the practical application of easily prepared, processable, and cost-effective hydrophilic self-contained microporous polymer membranes in ion transport applications.     

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.     

Sweet Potato Starch Microparticles as Controlled Drug Release Carriers: Preparation and In Vitro Drug Release

The aim of this study was to investigate the in vitro drug release behavior of sweet potato starch (SPS) microparticles intended for controlled drug delivery applications. Diclofenac sodium (DS) was used as a model drug candidate in the present study. SPS microparticles were prepared using a spray-drying technique by varying the polymer concentration and drug loading. The mean particles size of drug-loaded spray-dried SPS microparticles was between 10.3 and 13.1 µm. The mean particle size increased slightly with increase in the concentration of SPS. The mean particle size of spray-dried SPS microparticles increased from 10.3 to 13.1 µm when the concentration of SPS increased from 2 to 4% w/v. Under the current spray-drying conditions, the percentage yield of spray-dried SPS microparticles did not vary much among the various formulations and it was between 65.2 and 70.1%. The encapsulation efficiencies of SPS microparticles formulations was between 95.1–98.2%, suggesting good encapsulating ability of the SPS polymer by spary drying. Drug release from all the formulations of spray-dried SPS microparticles was controlled over period of 6 h. The cumulative amount of drug release from the spray-dried SPS microparticles decreased with an increase in the concentration of SPS, while it increases as the drug loading is increased. Release of the drug from spray-dried SPS microparticles followed Fick's law of diffusion since a good correlation coefficient (R²) was observed with the Higuchi plots (R² = 0.9928 to 0.9979).     

Ion‐Selective Ionic Polymer Metal Composite (IPMC) Actuator Based on Crown Ether Containing Sulfonated Poly(Arylene Ether Ketone)

This study introduces the concept of ion selective actuation in polymer metal composite actuators, employing crown ether bearing aromatic polyether materials. For this purpose, sulfonated poly(arylene ether ketone) (SPAEK) and crown ether containing SPAEK with molar masses suitable for membrane preparation are synthesized. The synthesized polymers are characterized using Nuclear magnetic resonance (NMR) and fourier transform infrared spectroscopy (FTIR) spectroscopy, thermal gravimetric analysis (TGA), and differential scanning calorimetry (DSC). Ionic polymer metal composite (IPMC) actuators are fabricated by electroless chemical deposition of a platinum (Pt) layer on both sides of SPAEK and crown‐ether containing SPAEK membranes, resulting in electrode layers of around 120 nm thickness. Actuation experiments demonstrate cation specific responses and bending degrees of the IPMC actuators. Incorporation of crown ether units in the polymer backbone results in an improved and ion‐selective bending displacement compared with SPAEK actuators. S(25)C(50)PAEK actuators show an increased bending displacement of 28% for Na⁺ and 20% for K⁺ ions.

     

Electrical Actuation of Coated and Composite Fibers Based on Poly[ethylene-co-(vinyl acetate)]

Robots are typically controlled by electrical signals. Resistive heating is an option to electrically trigger actuation in thermosensitive polymer systems. In this study electrically triggerable poly[ethylene-co-(vinyl acetate)] (PEVA)-based fiber actuators are realized as composite fibers as well as polymer fibers with conductive coatings. In the coated fibers, the core consists of crosslinked PEVA (cPEVA), while the conductive coating shell is achieved via a dip coating procedure with a coating thickness between 10 and 140 µm. The conductivity of coated fibers σ = 300–550 S m⁻¹ is much higher than that of the composite fibers σ = 5.5 S m⁻¹. A voltage (U) of 110 V is required to heat 30 cm of coated fiber to a targeted temperature of ≈ 65 °C for switching in less than a minute. Cyclic electrical actuation investigations reveal ε′_rev = 5 ± 1% reversible change in length for coated fibers. The fabrication of such electro-conductive polymeric actuators is suitable for upscaling so that their application potential as artificial muscles can be explored in future studies.     

Dual-Responsive Soft Actuator Based on Aligned Carbon Nanotube Composite/Graphene Bimorph for Bioinspired Applications

Nanocarbon-based polymer actuators have attracted significant attention because of their excellent actuation performance. In this study, a soft bimorph actuator composed of an anisotropic carbon nanotube (CNT)–polymer composite and reduced graphene oxide (rGO) film is fabricated by a simple blade-coating method. Owing to the excellent electrical, optical, and thermal properties of the CNT and rGO, the actuator exhibits dual-responsive actuation. It generates reversible bending deformation with a displacement of ≈13 mm under low electrical voltage stimulation or white light irradiation. Furthermore, because of the embedment of aligned CNTs in polymer matrix, this actuator exhibits excellent mechanical output compared with many of the reported nanocarbon-based actuators. It can lift a 2.048 g clip to a height of ≈5 mm under low electrical voltage stimulation. Based on this soft actuator with dual response and good mechanical output, various bionic devices are designed. A bionic eagle claw that grasps a soft object under electrical stimulation and an artificial flower blooming in response to light irradiation are constructed. Moreover, a light-driven smart curtain and a seagull robot are fabricated. These results reveal the great potential of the dual-responsive anisotropic soft actuator in soft robots and smart devices driven by electricity and light.     

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°).     

Vegetable fillers for electric stimuli responsive elastomers

Dielectric elastomer actuators (DEAs) have been studied widely in recent years for artificial muscle applications, but their implementation into production is limited due to high operating voltages required. The actuation behavior of dielectric elastomer under an applied electric field is predicted by Maxwell's pressure and thickness strain equations. According to these equations, the best electromechanical response is achieved when the relative permittivity is high and elastic modulus is low. The potential source for additives increasing the relative permittivity of rubbers can be vegetable powders that have much higher dielectric constant than common elastomers. In the present research, the dielectric and actuation properties of polyacrylate rubber (ACM) were studied after the addition of different vegetable‐based fillers such as potato starch, corn starch, garlic, and paprika. The results were compared to ACM filled with barium titanate. The compounds containing vegetable fillers showed higher relative dielectric permittivity at 1 Hz frequency than the compounds containing barium titanate due to higher interfacial polarization. The actuation studies showed that lower electric fields are required to generate certain actuation forces when the starches and garlic are used in the rubber instead of barium titanate. Therefore, the vegetable‐based fillers can be used to improve actuation performance of DEAs. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45081.     

Progress in the Field of Water‐ and/or Temperature‐Triggered Polymer Actuators

Water‐ and/or temperature‐triggered polymer actuators have great potential in robotics, microfabrication and micromanipulation, cell culture, artificial scaffolds, muscles, and motors. In the past few years, a large amount of work has been carried out, and several innovative concepts have been proposed to address challenges such as actuation with large‐scale displacement in a very short time, actuation of large‐sized samples, complex 3D shaping, directional control, multiresponsive actuation, and strong actuators. Herein, the progress made in the field of actuators triggered by water, temperature, and a combination of both is presented, emphasizing the new concepts of fast and direction‐controlled actuation, the corresponding mechanisms, the associated challenges, and future tasks and perspectives.     

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.     

Electric deformation response of anion-exchange membrane/gold composites

In previous papers, actuation phenomena of solid polymer electrolyte membrane (SPM)/metal (M) composites which can be controlled by small electric signals were reported. The actuation response has been applied to various applications as electrically controllable actuators. The solid polymer electrolyte membranes used in the previous reports were cation-exchange type. In this study, the similar response of the anion-exchange membrane/metal composite has been investigated in order to clarify the response mechanism of the SPM/M composite. A chemical plating method of forming gold on the surfaces of the anion-exchange membrane is developed. The composite was found to bend to the cathode side. The specific displacement was proportional to the amount of charge accumulated in the electrode. The quantitative electrokinetic model of the electric mechanical response of the SPM/M composite was developed, which attributes the response to the stress induced by the water-drag associated with the movement of the counterion in the membrane, which is the same basis as the case of the cation-exchange membrane. The experimental results were successfully explained by using the model.     

Effect of Yb3+ concentration on the green-yellow upconversion emission of SrGe4O9:Er3+ phosphors

This work presents the structural, morphological and luminescent, properties of SrGe₄O₉ (SGO):Er³⁺,Yb³⁺ phosphors. These phosphors were synthesized by simple combustion synthesis and subsequently annealed at 1100 °C. The XRD patterns revealed that all the SGO samples doped with Yb³⁺ concentrations from 2 to 10 at.% presented a trigonal pure phase (the Er³⁺ concentration was fixed to 1 at.%). The morphology of the SGO samples was analyzed by scanning electron microscopy and found that they are formed by microparticles with irregular shapes and average sizes in the range of 0.2 μm–3 μm. The luminescence measurements of the SGO:Er³⁺,Yb³⁺ samples showed the presence of two main emission bands at 551 nm (green) and at 662 nm (red) under excitation at 980 nm, which are associated to Er³⁺ transitions. For Yb concentration of 2 and 3 at.% the green band dominated, but the red band became more intense for Yb concentrations above 5 at.%. As result, the CIE coordinate changed from the green to the yellow region. The increase for the Yb content from 2 to 10 at.% also enhanced of the NIR emission of Er³⁺ ≈5 times and the maximum upconversion emission was observed for 8% of Yb concentration. Further, the surface of the SGO samples was analyzed by the FTIR technique in order to find OH groups which are common luminescent quenching centers, but these groups were not detected on the samples. Since the SGO samples presented tunable emission, absence of OH groups on their surface and stable crystalline structure for high Yb dopant concentrations, they could be good candidates as phosphors for solid state lighting or displays applications.