The Enhancement Effect of Mesoporous Graphene on Actuation of Nafion‐Based IPMC

A facile method to fabricate ionic polymer‐metal composite (IPMC) actuators is proposed. A blend of mesoporous graphene (MG) and Nafion is used as the ionic matrix, which is sandwiched by two layers of blend of reduced graphene oxide (rGO) and Nafion as the electrodes. When subjected to an electrical field of 3 V, the IPMC actuator exhibits a blocking force of 10 gf g^?1 for 20 s, and the same behavior can be repeatedly played for hundreds of cycles. MG improves the mechanical properties of Nafion‐based IPMC, more importantly, the mesopores in graphene provide additional pathway for the diffusion of cationic clusters and thus enhance the actuation speed. In addition, the surface electrodes of rGO protect the interlamellar liquid from evaporation thus ensure the durability.

     

Characterization and actuation behavior of SPS/SGO ion exchange polymer actuator based on PEDOT: PSS/SGO composite electrode

ABSTRACT

This paper studied the fabrication of new hybrid-type poly(3,4- ethylene dioxythiophene) (PEDOT)/sulfonated graphene oxide electrode-based polymer actuator produced by film casting method. Sulfonated Poly(1,4-phenylene ether-ether sulfone) (SPS) ion-exchange polymer membrane-based ionic polymer composite actuators were fabricated using the different concentration of SGO. The characterization and actuation were demonstrated. By altering SGO concentration, four different SPS based membrane actuators were analyzed. The effects of SGO concentration on the morphology, proton conductivity, ion exchange capacity, and water uptake capability were studied. The maximum tip displacement and force by varying concentration of SGO were evaluated for the actuation performance.     

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.     

Enhanced transport properties in polymer electrolyte composite membranes with graphene oxide sheets

Polymer electrolyte membranes have been widely investigated for high performance fuel cells. Here, we report the synthesis of ionic conductive Nafion/graphene oxide (GO) composite membranes for application in direct methanol fuel cells. GOs interact with both the non-polar backbone and the polar ionic clusters of Nafion because of their amphiphilic characteristics attributable to hydrophobic conjugation and hydrophilic functional groups. Accordingly, GO sheets serve to modify the microstructures of two domains of Nafion. In particular, the transport properties of Nafion are favorably manipulated by the incorporation of GO. This modulated the ionic channels of Nafion and decrease methanol crossover while preserving ionic conductivity. Furthermore, strong interfacial interactions due to the insertion of GO nanofillers into the Nafion matrix improve the thermal and mechanical properties of the material. In particular, we exploit Nafion/GO composite membrane as electrolyte material for direct methanol fuel cell (DMFC) in order to resolve current issue of methanol crossover. This composite membrane-based DMFC compared to the Nafion 112-based DMFC remarkably enhanced cell performance, especially in severe operating conditions.     

Influence of additives on the properties of casting nafion membranes and SO‐based ionic polymer–Metal composite actuators

As a typical smart material, ionic polymer metal composite (IPMC) has a sandwich structure, which consists of a base membrane and two thin metallic electrodes on both sides of the base membrane. The properties of the base membrane, Nafion as the most used base material, strongly affect the performance of IPMC actuator. This paper reports the effects of different additives, such as ethylene glycol (EG), dimethyl sulfoxide (DMSO), N, N′‐dimethyl formamide (DMF), and N‐methyl formamide (NMF), on the performances of the casting membranes and SO‐based IPMC actuators. Studies have shown that the microstructures of the casting membranes with EG and DMSO as additives are more loose and amorphous, leading to higher water contents and thus higher conductivity than those with DMF, NMF, and Nafion 117. Among the casting membrane‐based IPMC actuators, EG‐based IPMC actuator has larger deformation and blocking force, higher strain energy density and conversion efficiency at 2 V DC voltage, whose electromechanical properties are most close to that based on Nafion 117. POLYM. ENG. SCI., 54:818–830, 2014. © 2013 Society of Plastics Engineers     

Investigation of silicone rubber composites reinforced with carbon nanotube,nanographite, their hybrid,and applications for flexible devices

New technology is constantly required for updating new generation flexible devices, such as stretchable sensors, flexible electronics, and actuators. In the present study, a stretchable strain sensor, and actuator were developed based on room-temperature-vulcanized (RTV) silicone rubber reinforced with carbon nanotubes (CNTs), nanographite (GR), and CNT-GR hybrids. A CNT-based strain sensor developed for RTV silicone rubber showed improved stiffness and brittleness. For example, at 5 phr of filler loading, the compressive and tensile modulus for the CNT-reinforced RTV silicone matrix improved by 287% and 240%, respectively. Similarly, the improvements in the compressive and tensile modulus were moderate for the CNT-GR hybrid (210% and 235%) and low for GR (135% and 125%). The improved brittleness resulted in a higher fracture strain of 170% and 155% for the CNT-GR hybrid and GR, respectively. The improved mechanical properties were tested in real-life applications of actuation. The actuation displacement at a filler loading of 2 phr increased to 1.65 mm (CNT), 1.25 mm (CNT-GR), and 0.08 mm (GR). From 2 to 8 kV, the actuation displacement increased by 825% (CNT), 830% (CNT-GR), and 32% (GR). The strain sensor showed a stretchability of >100% (CNT) and >100% (CNT-GR). In addition, the gauge factor was higher for the CNT-GR hybrid composites. The durability measurements showed that the change in resistance was negligible for up to 5000 cycles in both the CNT and CNT-GR rubber composites. A series of experiments confirmed that compared to the composite based on RTV silicone rubber and CNT, the CNT-GR hybrid showed a robust flexibility and stretchability as a piezo-resistive strain sensor and actuator.     

Amplified immunosensing based on ionic liquid-doped chitosan film as a matrix and Au nanoparticle decorated graphene nanosheets as labels

This paper describes a new signal amplification strategy based on ionic liquid-doped chitosan film as a matrix and Au nanoparticle decorated graphene nanosheets (AuNP–graphene) as labels for the sensitivity improvement of an electrochemical immunosensor. At first, an ionic liquid was doped into ferrocene-branched chitosan film to obtain a novel redox composite, which was employed as an antibody immobilization matrix due to its better biocompatibility and higher electron transfer mobility. Then, the AuNP–graphene were prepared by a one-pot method in a aqueous-phase synthesis and were provided with a large surface area and multiple binding sites to allow high accessibility for the immobilization of secondary antibody (Ab2) and horseradish peroxidase (HRP). Based on the sandwich immunoassay format, the electrochemical signal could be amplified and adequately achieved, according to the catalytic reaction of the carried HRP towards the reduction of H₂O₂ with the aid of the IL and ferrocene synergistic effect. Using Immunoglobulin G (IgG) as a protein model, a good and repeatable linear relationship was found between the electrical signal outputs and human IgG concentration on a logarithm scale for a wide range of 2.0 × 10⁻¹⁰ to 5.0 × 10⁻⁷ g/mL, with a detection limit of 50 pg/mL. In conclusion, the use of ionic liquid-doped chitosan redox film and AuNP–graphene greatly enhances the electrochemical signal and shows high sensitivity.     

Influence of electrolytes of Li salts,EMIMBF4, and mixed phases on electrochemical and physical properties of Nafion membrane

Electrolyte‐soaked Nafion is commonly used as an ionic polymer in soft actuators. Here, a multitechnique investigation was applied to correlate the electrochemical behavior of Nafion membranes with their microstructures and nanostructures as a function of electrolyte type. The influence of electrolytes of Li salts with different counteranions on the Nafion membranes was investigated in terms of hydration level, structure (using X‐ray diffraction and small angle X‐ray scattering), stress–strain characteristics, and electrochemical behavior (by cyclic voltammetery and electrochemical impedance spectroscopy). The effects of using ionic liquid (IL), as the electrolyte, addition of different supporting solvent and the addition of Li⁺ ions to water‐free IL‐soaked membranes on the structural and electrochemical properties of Nafion were examined. The nano‐ and microstructure of the Nafion changed considerably as a function of the identity of the electrolyte solution. The electrochemical behavior of the IL‐soaked samples was compared with that of the water‐soaked Li⁺‐exchanged Nafion. It was seen that the ionic conductivity of the Nafion membranes was reduced significantly when water was replaced by pure IL. Using the supporting solvents increased the conductivity of IL‐soaked Nafion membranes dramatically. The presence of a small amount of Li⁺ ions together with the IL ions caused a significant decrease in charge transfer resistance and increases in double layer capacitance and in ionic conductivity over that of the water‐free sample and also over water‐soaked Li⁺‐exchanged Nafion. These findings can be useful to improve the knowledge on Nafion's microstructure and also to improve the electromechanical behavior of Nafion‐based ionic polymer–metal composites actuators. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 45239.     

Low percolation threshold of graphene/polymer composites prepared by solvothermal reduction of graphene oxide in the polymer solution

Graphene/polyvinylidene fluoride (PVDF) composites were prepared using in-situ solvothermal reduction of graphene oxide in the PVDF solution. The electrical conductivity of the composites was greatly improved by doping with graphene sheets. The percolation threshold of such composite was determined to be 0.31 vol.%, being much smaller than that of the composites prepared via blending reduced graphene sheets with polymer matrix. This is attributed to the large aspect ratio of the SRG sheets and their uniform dispersion in the polymer matrix. The dielectric constant of PVDF showed a marked increase from 7 to about 105 with only 0.5 vol.% loading of SRG content. Like the other conductor-insulator systems, the AC conductivity of the system also obeyed the universal dynamic response. In addition, the SRG/PVDF composite shows a much stronger nonlinear conduction behavior than carbon nanotube/nanofiber based polymer composite, owing to intense Zener tunneling between the SRG sheets. The strong electrical nonlinearity provides further support for a homogeneous dispersion of SRG sheets in the polymer matrix.     

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.     

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.     

新型细菌纤维素基阻醇质子交换膜的制备及表征

以凝胶贴附法,在Nation膜两侧贴附细菌纤维素（BC）膜,制备出BC／Nation／BC夹心复合膜,以期结合Nation膜的良好导电性和BC膜的优秀阻醇性,制备新型阻醇质子交换膜。利用扫描电镜、热重分析对其形态结构和热稳定性进行研究,并对夹心膜的尺寸稳定性、质子传导率和甲醇渗透率进行表征。结果发现,复合膜的夹心结构紧密,热稳定性良好,尺寸稳定性比市售的Nation膜有很大改善,提高了43％。夹心膜的质子传导率随温度的升高明显上升,虽略低于Nation膜,但是甲醇渗透率明显降低一个数量级,阻醇性能得到了很大改善。组装成电池后,单电池开路电压达到922mV,最大发电功率密度为7．2mW／cm^2。该结果表明夹心复合膜作为新型质子交换膜应用于直接甲醇燃料电池中具有很大潜力。     

Influence of Sulfonated Graphene Oxide on Sulfonated Polysulfone Membrane for Direct Methanol Fuel Cell

Novel proton exchange membranes consisting of an inorganic filler, namely sulfonated graphene oxide, embedded in sulfonated polysulfone were fabricated. The membrane performance depended on the sulfonated graphene oxide content possessed the functional groups to provide the interfacial interaction with sulfonated polysulfone through ionic channels and blocking effect. The membrane with 3% v/v sulfonated graphene oxide content embedded in the matrix was shown to be suitable for direct methanol fuel cell applications. The membrane exhibited the highest proton conductivity of 4.27?×?10^?3 S cm^?1 which was higher than that of Nafion117. Moreover, the membrane provided the lowest methanol permeability of 3.48?×?10^?7?cm²/s which was lower than that of Nafion117.     

Fabrication of graphene films on TiO2 nanotube arrays for photocatalytic application

Graphene film was formed on the surface of titanium dioxide nanotube (TiO₂ NT) arrays through in situ electrochemical reduction of a graphene oxide dispersion by cyclic voltammetry. The residual oxygen-containing groups and other structural defects such as sp³-hybridized carbons in the electrodeposited graphene were further removed by photo-assisted reduction of the underlying TiO₂ NTs, thus achieving the maximum restoration of π-conjugation in the graphene planes. Spectroscopic, electrochemical, and photoelectrochemical techniques were used to characterize the graphene films, and the use of the resulting graphene–TiO₂ NT material in photocatalysis was investigated. The results showed that the graphene–TiO₂ NT material exhibited a greatly improved photocatalytic activity compared with unmodified TiO₂ NTs.     

Preparation of functionalized graphene/linear low density polyethylene composites by a solution mixing method

The surface modification of graphene as well as the characterization of modified graphene-based polymer composite prepared by solution mixing techniques was examined. X-ray photoelectron spectroscopy was employed to examine the surface modification and formation of graphene. The tensile strength of the composite increased with 3 wt.% of DA-G loading and was 46% higher than that of neat LLDPE. The onset thermal degradation temperature of the composite (3 wt.% of DA-G) was increased by ∼40 °C compared to neat LLDPE. A sharp increase in electrical conductivity of the composite was observed at 3 wt.% of DA-G content.     

Preparation and testing of Nafion/titanium dioxide nanocomposite membrane electrode assembly by ultrasonic coating technique

Membrane electrode assemblies with Nafion/nanosize titanium dioxide (TiO₂) composite membranes were manufactured with a novel ultrasonic‐spray technique (UST) and tested in proton exchange membrane fuel cell (PEMFC). The structures of the membranes were investigated by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and thermogravimetric analysis. The composite membranes gained good thermal resistance with insertion of TiO₂. The SEM and XRD techniques have proved the uniform and homogeneous distribution of TiO₂ and the consequent enhancement of crystalline character of these membranes. The existence of nanometer size TiO₂ has improved the thermal resistance, water uptake, and proton conductivity of composite membranes. Gas diffusion electrodes were fabricated by UST. Catalyst loading was 0.4 (mg Pt) cm^?2 for both anode and cathode sides. The membranes were tested in a single cell with a 5 cm² active area operating at the temperature range of 70°C to 110°C and in humidified under 50% relative humidity (RH) conditions. Single PEMFC tests performed at different operating temperatures indicated that Nafion/TiO₂ composite membrane is more stable and also performed better than Nafion membranes. The results show that Nafion/TiO₂ is a promising membrane material for possible use in PEMFC at higher temperature. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40541.     

Nafion-impregnated polyethylene-terephthalate film used as the electrolyte for direct methanol fuel cells

An electrolyte system for direct methanol fuel cells (DMFC) was prepared by basing its design on combination of the existing concepts such as a composite membrane and a barrier against methanol cross-over. A composite membrane was prepared by impregnating Nafion ionomer into 6 μm thick hydrophilic PETE (polyethylene-terephthalate) film whose average pore diameter was 0.3 μm. Owing to some features of the film such as high mechanical strength and less than 30% of its surface being occupied by the openings for proton passage, it was far more effective to block the passage with a very thin palladium film with the aim of preventing methanol cross-over. The DMFCs utilizing such a thin composite membrane as the electrolyte exhibited improved performances over those using conventional Nafion in the possibility of ambient temperature operation, higher current densities, and substantial reduction of methanol cross-over.     

Thermomechanical properties of chemically modified graphene/poly(methyl methacrylate) composites made by in situ polymerization

The morphology and thermomechanical properties of composites of poly(methyl methacrylate) (PMMA) and chemically modified graphene (CMG) fillers were investigated. For composites made by in situ polymerization, large shifts in the glass transition temperature were observed with loadings as low as 0.05 wt.% for both chemically-reduced graphene oxide (RG-O) and graphene oxide (G-O)-filled composites. The elastic modulus of the composites improved by as much as 28% at just 1 wt.% loading. Mori–Tanaka theory was used to quantify dispersion, suggesting platelet aspect ratios greater than 100 at low loadings and a lower quality of dispersion at higher loadings. Fracture strength increased for G-O/PMMA composites but decreased for RG-O/PMMA composites. Wide angle X-ray scattering suggested an exfoliated morphology of both types of CMG fillers dispersed in the PMMA matrix, while transmission electron microscopy revealed that the platelets adopt a wrinkled morphology when dispersed in the matrix. Both techniques suggested similar exfoliation and dispersion of both types of CMG filler. Structural characterization of the resulting composites using gel permeation chromatography and solid state nuclear magnetic resonance showed no change in the polymer structure with increased loading of CMG filler.     

Sulfonated poly(ether sulfone)/phosphotungstic acid/attapulgite composite membranes for direct methanol fuel cells

Novel composite sulfonated poly(ether sulfone)(SPES)/phosphotungstic acid (PWA)/attapulgite (AT) membranes were investigated for direct methanol fuel cells (DMFCs). Physical–chemical properties of the composite membranes were characterized by FTIR, DSC, TGA, SEM‐EDX, water uptake, tensile test, proton conductivity, and methanol permeability. Compared with a pure SPES membrane, PWA, and AT doping in the membrane led to a higher thermal stability and glass transition temperature (T_g) as revealed by TGA and DSC. Tensile test indicated that lower AT content (3%) in the composite can significantly increase the tensile strength, while higher AT loading demonstrated a smaller contribution on strength. Proper PWA and AT loadings in the composite membranes can increase the proton conductivity and lower the methanol cross‐over. The proton conductivity of the SPES‐P‐A 10% composite membrane reached 60% of the Nafion 112 membrane conductivity at room temperature while the methanol permeability was only one‐fourth of that of Nafion 112 membrane. This excellent performances of SPES/PWA/AT composite membranes could indicate a potential feasibility as a promising electrolyte for DMFC. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011