Novel conducting fabric polymer composites as stretchable electrodes: one‐step fabrication of chemical actuators

Composite films have functioned as chemical bending actuators, where stretchable conducting fabrics were joined to both surfaces of ionomer films. This phenomenon shows that a direct metallization of either electroless or electrolytic plating having a metal dendrite formation on the ionomer film is not essential for functioning as actuators. Conducting fabric polymer composite (CFPC) actuators can be easily fabricated by a simple adhesion process using flexible conducting fabrics as electrodes. Due to their excellent contraction and expansion capabilities, gold‐ and copper‐plated knitted fabrics were employed and stably bound to Nafion‐117 film. Au‐CFPC actuators demonstrated a maximum bending displacement of ±2.5 mm at ±2 V. Cu‐CFPC gave a smaller displacement of ±0.7 mm at ±2 V, having no reverse displacement. The method described here is widely applicable, introducing conducting layers on various flexible, stretchable, and polymer substrates. Copyright © 2008 John Wiley & Sons, Ltd.     

Plasticizer and catalyst co-functionalized PEDOT:PSS enables stretchable electrochemical sensing of living cells

Recently, stretchable electrochemical sensors have stood out as a powerful tool for the detection of soft cells and tissues, since they could perfectly comply with the deformation of living organisms and synchronously monitor mechanically evoked biomolecule release. However, existing strategies for the fabrication of stretchable electrochemical sensors still face with huge challenges due to scarce electrode materials, demanding processing techniques and great complexity in further functionalization. Herein, we report a novel and facile strategy for one-step preparation of stretchable electrochemical biosensors by doping ionic liquid and catalyst into a conductive polymer (poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate), PEDOT:PSS). Bis(trifluoromethane) sulfonimide lithium salt as a small-molecule plasticizer can significantly improve the stretchability and conductivity of the PEDOT:PSS film, and cobalt phthalocyanine as an electrocatalyst endows the film with excellent electrochemical sensing performance. Moreover, the functionalized PEDOT:PSS retained good cell biocompatibility with two extra dopants. These satisfactory properties allowed the real-time monitoring of stretch-induced transient hydrogen peroxide release from cells. This work presents a versatile strategy to fabricate conductive polymer-based stretchable electrodes with easy processing and excellent performance, which benefits the in-depth exploration of sophisticated life activities by electrochemical sensing.

A facile strategy for constructing stretchable sensors with excellent mechanical, electrochemical and biocompatible performance is developed, and in situ inducing and monitoring of stretch-evoked H₂O₂ release from cells has been successfully achieved.     

Using Transparent Adhesive Tape as New Substrate for Integrated Flexible Enzymatic Sensor: Good Adhesion and Better Printability

Substrate plays an essential role in the construction of flexible electrode and related wearable sensors. Compared with conventional flexible substrates such as Polyethylene terephthalate (PET), the common transparent adhesive tape exhibits the unique advantages in the non-adhesive surface with good printability, allowing the conductive layer to be deposited directly on its surface, and in another adhesive surface with good fastening, thus facilitating the fabrication of as-prepared electrode in subsequent wearable sensors. Herein, we constructed a new type of flexible sensor to detect ascorbic acid which is closely related to human health in sweat by integrating flexible electrode based on transparent adhesive tape with potentiostat that incorporate the critical signal conditioning, processing, and transmission functions. Experiment results show that resulting electrode still has the good electrochemistry performance even after 1000 bending cycles (20 % bending degrees). By connecting as-prepared flexible electrode to the potentiostat to carry out real time analysis, the resulting sensor exhibits excellent sensitivity, detection limit and repeatability (0.15 V detection potential vs printed Ag/AgCl reference electrode, 3.8 μM detection limit, 25 μM-1 mM linearity, and good selectivity).     

Synthesis of nickel nanoparticles supported on metal oxides using electroless plating: Controlling the dispersion and size of nickel nanoparticles

Nickel nanoparticles supported on metal oxides were prepared by a modified electroless nickel-plating method. The process and mechanism of electroless plating were studied by changing the active metal (Ag) loading, acidity, and surface area of metal oxides and were characterized by UV–vis spectroscopy, transmission electron microscopy, scanning electron microscopy, and H₂ chemisorption. The results showed that the dispersion of nickel nanoparticles was dependent on the interface reaction between the metal oxide and the plating solution or the active metal and the plating solution. The Ag loading and acidity of the metal oxide mainly affected the interface reaction to change the dispersion of nickel nanoparticles. The use of ultrasonic waves and microwaves and the change of solvents from water to ethylene glycol in the electroless plating could affect the dispersion and size of nickel nanoparticles.     

Electroless Nickel Plating and Electroplating on FBG Temperature Sensor

Metal-coated fiber Bragg grating（FBG）temperature sensors were prepared via electroless nickel（EN）plating and tin electroplating methods on the surface of normal bare FBG.The surface morphologies of the metal-coated layers were observed under a metallographic microscope.The effects of pretreatment sequence,pH value of EN plating solution and current density of electroplating on the performance of the metal-coated layers were analyzed.Meanwhile, the Bragg wavelength shift induced by temperature was monitored by an optical spectrum analyzer.Sensitivity of the metal-coated FBG（MFBG）sensor was almost two times that of normal bare FBG sensor.The measuring temperature of the MFBG sensor could be up to 280℃,which was much better than that of conventional FBG sensor.     

Stretchable Electrochemical Sensor for Real‐Time Monitoring of Cells and Tissues

Stretchable electrochemical sensors are conceivably a powerful technique that provides important chemical information to unravel elastic and curvilinear living body. However, no breakthrough was made in stretchable electrochemical device for biological detection. Herein, we synthesized Au nanotubes (NTs) with large aspect ratio to construct an effective stretchable electrochemical sensor. Interlacing network of Au NTs endows the sensor with desirable stability against mechanical deformation, and Au nanostructure provides excellent electrochemical performance and biocompatibility. This allows for the first time, real‐time electrochemical monitoring of mechanically sensitive cells on the sensor both in their stretching‐free and stretching states as well as sensing of the inner lining of blood vessels. The results demonstrate the great potential of this sensor in electrochemical detection of living body, opening a new window for stretchable electrochemical sensor in biological exploration.     

Stretchable touch sensitive keypad

We present a multifunctional and stretchable capacitive sensor capable of accurately detecting large strains, pressure and human touch. The device is prepared as a plate capacitor with stretchable thin gold film electrodes. Using conventional patterning techniques, a 3x3 array of stretchable sensors is prepared and implemented as a largearea 9-node touch pad. The array can operate when worn around the wrist or subjected to large deformations (>10% strain), measure pressure (up to 160kPa) and register touch applied with a finger, a metallic or plastic stylus.     

Development and investigation of the flexible hydrogen sensor based on ZnO-decorated Sb2O3 nanobelts

Hydrogen is regarded as the next-gen fuel for vehicles to avoid the emission of toxic gases, which needs a continuous monitoring of the concentration level. In the design of the H₂ sensor, especially of flexible type, a sensing layer will be blended, which affects the sensing performance of the device. Based on this concern, the present investigation is carried out to understand the effect of the bending angle toward the sensing performance of bare and ZnO (n-type)-decorated Sb₂O₃ (p-type) nanobelt–based sensors for hydrogen gas. The sensing element was prepared by the thermal chemical vapor deposition followed by the drop-casting method. Furthermore, the role of the zinc precursor (molar concentration—1 M–3 M) on the preparation of ZnO-decorated Sb₂O₃ nanobelts was studied. Various techniques were used to confirm the formation of ZnO-decorated nanobelts such as X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDAX), and Fourier transform infrared spectroscopy (FTIR). From these analyses, 1 M concentration of the zinc precursor shows uniform distribution of nanoparticles over the surface of Sb₂O₃ nanobelts. However, agglomeration was observed when the concentration of the zinc precursor increases from 1 M to 3 M. Later, the prepared nanobelts were deposited on the OverHead Projector (OHP) sheet by the doctor blade method for sensing hydrogen gas at 100 °C at a concentration of 1000–3000 ppm. In addition to it, the effect of the substrate bending angle (0°, 45°, 60°, and 90°) was analyzed at a fixed concentration of H₂ gas (1000 ppm). From this study, it is clear that the highest sensing response was achieved for 1 M decorated nanobelts compared with bare as well as other concentrations because of uniform distribution of nanoparticles on the surface of nanobelts. Moreover, the prepared sample demonstrates better sensing performance with the bending of substrates, which suggests that the prepared sensor could be used for flexible electronic devices. The prepared nanobelts show a good H₂ gas–sensing response even with bending of the substrates. The work suggests that the prepared sensor is applicable for flexible electronic devices.     

Highly Ordered 3D Porous Graphene Sponge for Wearable Piezoresistive Pressure Sensor Applications

Wearable sensors with excellent flexibility and sensitivity have emerged as a promising field for healthcare, electronic skin, and so forth. Three-dimensional (3D) graphene sponges (GS) have emerged as high-performance piezoresistive sensors; however, problems, such as limited flexibility, high cost, and low sensitivity, remain. Meanwhile, device-level wearable pressure sensors with GS have rarely been demonstrated. In this work, highly ordered 3D porous graphene sponges (OPGSs) were first successfully prepared and controlled through an emulsion method, and then a device-level wearable pressure sensor with high flexibility and sensitivity was assembled with a gold electrode and polydimethylsiloxane into a reliable package. The pH values were carefully controlled to form a stable emulsion and the OPGSs showed a highly ordered 3D structure with ultralow density, high porosity, and conductivity; this resulted in a gauge factor of 0.79–1.46, with 50 % compression strain and excellent long-term reproducibility over 500 cycles of compression–relaxation. Moreover, the well-packaged pressure sensor devices exhibited ultrahigh sensitivity to detect human motions, such as wrist bending, elbow bending, finger bending, and palm flexing. Thus, the developed pressure sensors exhibited great potential in the fields of human-interactive applications, biomechanical systems, electronic skin, and so forth.     

H2S gas sensor based on integrated resonant dual-microcantilevers with high sensitivity and identification capability

Detection of trace-level hydrogen sulfide (H₂S) gas is of great importance whether in industrial production or disease diagnosis. This research presents a novel H₂S gas sensor based on integrated resonant dual-microcantilevers which can identify and detect trace-level H₂S in real-time. The sensor consists of two integrated resonant microcantilever sensors with different functions. One cantilever sensor can identify H₂S by outputting positive frequency shift signals, while the other cantilever sensor will detect H₂S as a normally used cantilever sensor with negative frequency shifts. Combined the two cantilever sensors, the proposed gas sensor can distinguish H₂S from a variety of common gases, and the detection limit to H₂S of the sensor is as sensitive as below 1 ppb.     

Preparation of palladium composite membranes by modified electroless plating procedure

A thin palladium composite membrane was produced by modified electroless plating procedure. Compared with the conventional electroless plating procedure, the modified electroless plating procedure consists of the activation of a ceramic substrate by the sol–gel process of a Pd(II)-modified boehmite sol. Additionally, the infiltration of an electroless plating solution to a porous substrate during the deposition of palladium was employed with the filter device to improve adherence of a palladium layer to a substrate. The resulting membrane with a thickness of about 1 μm has a high compactness. The membrane shows a hydrogen selectivity of 20–130 for H₂/N₂, and a hydrogen flux of 1.8–87 m³/m²·h, depending on operation conditions.     

Influence of temperature on the surface property of ABS resin in KMnO4 etching solution

The KMnO₄-H₃PO₄-H₂SO₄ system was used to roughen and hydrophilically modify on the surface of ABS resin at different etching temperatures, and then, electroless nickel plating process was carried out. The surface of ABS resin after etching was characterized by XPS and SEM. It is found that the surface etching effect of ABS resin is relatively good when the etching temperature is 65°C. The resin surface generates ─OH and ─COOH hydrophilic groups, the roughness of resin surface is increased significantly, and the surface hydrophilic contact angle is 40.51°. After electroless nickel plating on the ABS etching surface, the bonding force of the coating can reach 2.73 MPa. Electrochemical polarization curves and electrochemical impedance spectra also show that the corrosion resistance of coating after 65°C etching postprocessing is improved.     

有机相化学镀铝法制备Al/石墨烯复合材料粉末

采用有机相化学镀法制备了Al/石墨烯复合材料粉末。使用傅里叶红外光谱仪、拉曼光谱仪、ASAP2020全自动快速比表面与孔隙度分析仪和配备EDS能谱的扫描电子显微镜表征样品。结果表明,镀铝后,石墨烯表面的含氧基团基本消失,发生空间弯曲折叠形成包覆结构,导致中孔和大孔的形成,石墨烯层间距变大。此外,氮气吸附-脱附结果显示,Al/石墨烯复合材料粉末的孔道以微孔和中孔为主,Brunauer-Emmett-Teller比表面积为91 m~2·g~(-1);通过Barret-Joyner-Halenda解吸模型计算得到的平均孔径为8.77 nm,孔体积为0.45 cm~3·g~(-1)。X射线衍射分析并没有发现Al_4C_3晶体结构的出现,表明镀铝过程并未或生成很少(小于检测下限)脆相Al_4C_3。最后,微观表面分析表明,当加入的NaH量略大于理论值时,实验结果与理想体系基本吻合,镀铝效果最佳。     

The influence of bending on the performance of flexible carbon black/polymer composite gas sensors

The performance of electronics on flexible substrates suffers under substrate bending leading to reduced device performance. In this article, we highlighted the influence of bending strain on a conductive polymer composite gas sensor and developed a model to investigate the influence of strain. We evaluated the strain influence on the resistance of a gas sensor with respect to sensitivity, filler content, cyclic loading, and electrode orientation. The sensitivity of gas sensors increased with decreasing tensile bending radii. The influence of strain was dominant for gas sensors with less carbon black concentration. Cyclic bending tests showed a decrease of sensor resistance versus time and a plastic deformation. A sensor geometry orientations effect to reduce the sensitivity to bending strain was achieved by aligning the electrode fingers parallel to the strain. A model was successfully implemented to simulate strain influences inside the polymer incorporating the Poisson ratio. We suggest a concept to achieve a strain insensitive gas sensor by creating an orientation between single particles inside the composite. Implementing this results into existing gas sensors will improve the measurement quality and reliability of sensors on flexible substrates. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2013     

Octahedral Cuprous Oxide Decorated Flexible Reduced Graphene Oxide Paper for Food Sensing Application

This work presents a simple method to fabricate an octahedral cuprous oxide (Cu₂O) decorated two-dimensional (2D) flexible rGOP electrode with filtration and electrodeposition strategies. The characteristic of the Cu₂O/rGOP electrodes was recorded by SEM, EDX, XPS, XRD, and Raman spectroscopy. The results clearly showed that Cu₂O was successfully electrodeposited on the surface of rGOP by controlling the electrodeposition potential without the introduction of any template or surfactant. The electrochemical characterizations of the Cu₂O/rGOP exhibited high electrocatalytic activity toward the reduction of H₂O₂. The linear detection range for the Cu₂O/rGOP flexible sensor was 5.0 μM to 5.5 mM, with a limit of detection of 1.27 μΜ. Subsequently, the developed flexible rGOP sensor was extended for H₂O₂ detection in milk samples for avoiding milk spoilage_. Such judicial preparation of rGOP as a sensing device will certainly pave the way for various other sensing applications including environmental and biomedical applications.     

Conductive Film with Flexible and Stretchable Capability for Sensor Application and Stealth Information Transmission

Flexible and wearable strain sensors for human-computer interaction, health monitoring, and soft robotics have drawn widespread attention to promising applications in the next generation of artificial intelligence devices. However, conventional semiconductor sensors are difficult to meet the requirements of flexibility and stretchability. Here, we reported a kind of novel and simple sensor based on layer-by-layer(LBL) method. Carbon nanotubes (CNTs) layer provides high ductility and stability in the process of tension sensing, while silver layer provides low initial resistance and fast reflecting in the process of tension sensing. LBL method ensures the uniformity of the conductive layer. The sensor has superior sheet resistance of 9.44Ω/sq., high elongation at break of 104%. For sensing capability, the sensor has wide reflecting range of 60%, high gauge factor (GF) of 1000 up to 60%strain, fast reflecting time of 165 ms. Excellent reliability and stability have also been verified. It is also worth mentioning that the entire process does not require any expensive equipments, complicated processes or harsh experimental conditions. The above features provide an idea for large-scale application of flexible stretchable sensors.     

Surface-Grafted Polymer-Assisted Electroless Deposition of Metals for Flexible and Stretchable Electronics

Surface-grafted polymers, that is, ultrathin layers of polymer coating covalently tethered to a surface, can serve as a particularly promising nanoplatform for electroless deposition (ELD) of metal thin films and patterned structures. Such polymers consist of a large number of well-defined binding sites for highly efficient and selective uptake of ELD catalysts. Moreover, the polymer chains provide flexible 3D network structures to trap the electrolessly deposited metal particles, leading to strong metal–substrate adhesion. In the past decade, surface-grafted polymers have been demonstrated as efficient nanoplatforms for fabricating durable and high-performance metal coatings by ELD on plastic substrates for applications in flexible and stretchable electronics. This focus review summarizes these recent advances, with a particular focus on applications in polymeric flexible and stretchable substrates. An outlook on the future challenges and opportunities in this field is given at the end of this paper.     

Rational design of a novel two-dimensional porous metal-organic framework material for efficient benzene sensor

As a common volatile organic compound, benzene (C₆H₆) exists in home decoration pollution gas widely, which causes great harm to the environment and human health. Therefore, it is necessary to rationally design advanced materials with high selectivity to detect and capture C₆H₆. Herein, combined with the d-band center theory and cohesive energy, a new two-dimensional metal-organic framework material, Ni-doped hexaaminobenzene-based coordination polymer (Ni-HAB-CP) is designed, and its application potential as a C₆H₆ sensor are systematically investigated by using first principles calculation. The result shows that Ni-HAB-CP has a strong adsorption for C₆H₆ without any additional method. In addition, Ni-HAB-CP can maintain good conductivity before and after adsorption, and C₆H₆ can be easily desorbed from the surface of Ni-HAB-CP by charge control. Moreover, the I-V curve calculated by Atomistix Toolkit (ATK) reveals that Ni-HAB-CP has high sensitivity and selectivity to C₆H₆. Hence, Ni-HAB-CP is expected to be used as a potential material for a highly efficient and recyclable C₆H₆ sensor in the future. The calculation and analysis methods used in this paper could provide a certain theoretical basis and reference for the future research of gas sensors.     

Reflective and conductive surface‐silvered polyimide films prepared by surface graft copolymerization and electroless plating

Argon plasma‐pretreated polyimide (PI) films were subjected to UV‐induced surface graft copolymerization with 4‐vinylpyridine(4VP) under atmospheric conditions. Electroless plating of silver was carried out effectively on the 4VP graft copolymerized PI (PI‐g‐P4VP) surface after PdCl₂ activation and in the absence of SnCl₂ sensitization (the Sn‐free process). The surface compositions of the modified PI films were studied by X‐ray photoelectron spectroscopy (XPS). XPS results showed that the PI‐g‐P4VP surface is ready for electroless deposition of silver via the Sn‐free process. The grafted 4VP layer with well‐preserved pyridine groups was used not only as the chemisorption sites for the palladium complexes (without the need for prior sensitization by SnCl₂) during the electroless plating of silver, but also as an adhesion promotion layer for the electrolessly deposited silver. The silver metallized PI films show high reflectivity and conductivity with a surface resistance of 1.5 Ω and a reflectivity of 91.3%, respectively. Copyright © 2007 John Wiley & Sons, Ltd.     

An Overview of Stretchable Supercapacitors Based on Carbon Nanotube and Graphene

The wearable demand of modern electronic devices makes flexible and stretchable energy storage device urgently needed.Stretchable and flexible supercapacitors(SCs) are energy storage devices that provide ultrahigh power density while having long-term durability,high security, and electrochemical stability. Among different SCs electrode materials, CNTs and graphene-based materials exhibit great potential in terms of stretchable SCs due to its ultrahigh electrical conductivity, large specific surface area and good mechanical properties. In this review,the state-of-the-art process and achievements in the field of stretchable SCs enabled by CNTs and graphene are presented, which include the novel design strategy, mechanical and electrochemical properties. The final section highlights current challenges and future perspectives on research in this thriving field.