MXene Reinforced PAA/PEDOT:PSS/MXene Conductive Hydrogel for Highly Sensitive Strain Sensors

Conductive hydrogel has a vital application prospect in flexible electronic fields such as electronic skin and force sensors. Developing conductive hydrogel with significant toughness and high sensitivity is urgently needed for application research. In this work, a strong and sensitive strain sensor based on conductive hydrogel is demonstrated by introducing MXene (Ti3C2Tx) into the micelle crosslinked polyacrylic acid (PAA)/poly(3,4-ethylenedioxythiophene):poly(styrene-sulfonate) (PEDOT:PSS) hydrogel network. The functional polymer micelle crosslinkers can dissipate external stress by deformation, endowing the hydrogel with high strength. The combination of MXene both improves the polymer network structure and the conductive pathways, further enhancing the mechanical properties and sensing performance. Resultantly, the flexible strain sensor base on PAA/PEDOT:PSS/MXene conductive hydrogel exhibits excellent sensing performance with a high gauge factor of 20.86, a large strain detection range of 1000%, as well as good adhesion on different interfaces. Thus, it can be used to monitor various movements of the human body and identify all kinds of handwriting, showing great potential into wearable electronics.     

Double Network Hydrogel Sensors with High Sensitivity in Large Strain Range

Owing to their preferable flexibility and facilitation to integrate with various apparel products, flexible sensors with high sensitivity are highly favored in the fields of environmental monitoring, health diagnosis, and wearable electronics. However, great challenges still remain in integrating high sensitivity with wide sensing range in one single flexible strain sensor. Herein, a new stretchable conductive gel-based sensor exhibiting remarkable properties regarding stretchability and sensitivity is developed via improving the ionic conductivity of the PVA/P(AM-AANa) double network hydrogel. Specifically, the strain sensor developed exhibits an excellent elongation of 549%, good fatigue resistance, and recovery performance. Simultaneously, the hydrogel strain sensor shows a high conductivity of 25 mS cm⁻¹, fast response time of 360 ms, and a linear response (gauge factor = 4.75) to external strain (≈400%), which endow the sensor with accurate and reliable capacities to detect various human movements. Integrating the merits of flexibility, environment friendliness, and high sensitivity, the conductive gel-based sensor has promising application prospects in human–machine interfaces, touchpads, biosensors, electronic skin, wearable electronic devices, and so on.     

Magnetic nanocomposite hydrogel with ultra-stretchable as strain sensors for monitoring human motion and the change of magnetic field

In recent years, the smart hydrogels have gained much concern in the field of research specially related to flexible strain sensors because they exhibit many types of smart interactions that can be useful in wearable devices. However, the conventional hydrogels have poor electrical conductivity that affect the performance of the sensors, so it remains a challenge to achieve noncontact signal monitoring (e.g., for the detection of magnetic field changes). In this study, an ultra-stretchable and magnetically responsive conductive hydrogel was fabricated by adding magnetic ferric tetroxide@polypyrrole composite nanoparticles (Fe₃O₄@PPy NPs) to polyacrylamide (PAm). The nanoparticles were easily agglomerated and improved the compatibility of PPy and hydrogel. The obtained PAm/Fe₃O₄@PPy hydrogel showed an ultra-stretchability of (961%), a low elastic modulus of (87.8 kPa), and an excellent toughness of (1010.5 kJ m⁻³). Moreover, PAm/Fe₃O₄@PPy hydrogel also exhibited a high electrical conductivity of 0.34 S m⁻¹, and the PAm/Fe₃O₄@PPy hydrogel sensor could detect human motions (such as bending of finger, bending of wrist) and muscle micromotion (such as pronouncing). In addition, it can also monitor the change in magnitude of magnetic field.     

Preparation and properties of a form‐stable phase‐change hydrogel for thermal energy storage

In this study, we aimed to fabricate a form‐stable phase‐change hydrogel (PCH) with excellent mechanical properties and heat‐storage properties. Sodium alginate (SA) and polyacrylamide (PAAm) composite hydrogels were prepared with ionically crosslinked SA in a PAAm hydrogel network. Glauber's salt [i.e., sodium sulfate decahydrate (Na₂SO₄·10H₂O)] was incorporated within the hydrogel network as a phase‐change material. Scanning electron microscopy micrographs revealed that Na₂SO₄·10H₂O was confined in the micropores of the hydrogel inner spaces, and differential scanning calorimetry curves showed that the composite hydrogel possessed a considerable storage potential. Mechanical properties tests, such as tensile and compressive measurements, presented a decreasing trend with increasing Na₂SO₄·10H₂O dosage. We concluded that the prepared composite PCH could be used to design hydrogel materials with thermal‐energy‐storage applications. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43836.     

Fabrication of Cellulose Nanofiber/Reduced Graphene Oxide/Nitrile Rubber Flexible Films Using Pickering Emulsion Technology for Electromagnetic Interference Shielding and Piezoresistive Sensor

With the rapid development of flexible electronics, the demand for flexible electromagnetic interference (EMI) shielding materials is increasing. This study develops a new green and effective strategy, consisting of graphene oxide (GO) and cellulose nanofibrils (CNF) co-stabilized Pickering emulsion combined with hot-pressing technology, to prepare flexible and conductive nitrile rubber (NBR) composite films. The composite films consist of a 3D network conductive skeleton structure of reduced GO (RGO) and an isolated NBR structure. This specific design results in a maximum high conductivity of 99 S m⁻¹, which is higher by an order of magnitude compared with that of the composites obtained using the traditional solution blending method, and a stable EMI shielding effectiveness of 25.81 dB in the X band. The introduction of the flexible NBR results in the excellent flexibility and structural strength of the composite film, and exhibits a decrease of 2.51% in the EMI shielding efficacy after 5000 cycles. As a piezoresistive sensor for wearable devices, the CNF-RGO/NBR flexible film can hold precise current signals and respond to finger motion. The findings of this study can provide new insights for the design of conductive and flexible composites as wearable and portable medical equipment and electronic devices.     

Facile synthesis of flexible and free-standing cotton covered by graphene/MoO2 for lithium-ions batteries

It is necessary to build flexible and free-standing materials for flexible/wearable electronics in high-performance lithium-ions batteries. Herein, we design and fabricate a flexible and free-standing 3 D carbon/MoO₂ composite through a facile immersing method followed by an annealing process. The carbon framework is supported by non-woven cotton totally covered by graphene sheets. The nanosized MoO₂ particles were uniformly anchored on cotton fibers and graphene sheets. The structure has several advantages, such as an interconnected 3D electronically conductive network, plenty of channels for electrolyte solution cross, and more active points for the electrode reaction. Compared with cotton/MoO₂ (C/MoO₂) without graphene sheets, the CGN/MoO₂ composite (cotton covered by graphene/MoO₂) showed much better thermal stability and excellent cycling performance. The proposed synthesis process paves a new way as promising electrode materials for high power battery applications such as roll-up displays and wearable devices.     

导电水凝胶的制备及应用研究进展

导电水凝胶是一类将亲水性基质和导电介质有机结合的新型水凝胶,具有较高的柔韧性、可调的力学性能和优异的电化学性能,在柔性电子设备等领域具有广阔的应用前景。本文综述了导电水凝胶材料的研究前沿和动态,介绍了导电水凝胶的分类及制备方法,讨论了导电水凝胶的结构设计与性能,重点阐述了导电水凝胶材料的应用研究进展,归纳了导电水凝胶材料面临的问题与挑战,并展望了导电水凝胶材料的发展趋势,指出采用天然可再生资源为原料开发具有高导电性、力学性能稳定、耐极端温度、生物相容性和生物可降解的导电水凝胶将成为下一步研究重点,同时优化柔性电子装置、提高器件输出稳定性也将成为重要的研究方向之一。导电水凝胶的制备及应用研究将促进柔性电子功能材料领域的快速发展。     

Polyaniline/Poly(acrylamide‐co‐sodium acrylate) Porous Conductive Hydrogels with High Stretchability by Freeze‐Thaw‐Shrink Treatment for Flexible Electrodes

With the development of alternatives to traditional fossil energy and the rise of wearable technology, flexible energy storage devices have attracted great attention. In this paper, a polyaniline/poly(acrylamide‐sodium acrylate copolymer) hydrogel (PASH) with high flexibility and excellent electrochemical properties for flexible electrodes is fabricated by freeze‐thaw‐shrink treatment of a highly water‐absorptive hydrogel, together with in‐situ polymerization of aniline at a low aniline concentration (0.1 mol L^?1). The PASH exhibits a conductivity of 4.05 S m^?1 and an elongation at break of 1245%. The freeze‐thaw‐shrink treatment greatly improves the electrochemical performance and stability of the conductive PASH. The area specific capacitance of PASH reaches 849 mF cm^?2 and the capacitance maintains 89% after 1000 galvanostatic charge–discharge cycles. All the raw materials are conventional industrialized materials and no additional templating agent is needed during the entire synthesis process. This study provides a cost‐efficient approach for the fabrication of conductive polymer hydrogels, which has a broad application prospect in flexible energy storage electronic devices.     

2D Ti3C2Tx MXene/aramid nanofibers composite films prepared via a simple filtration method with excellent mechanical and electromagnetic interference shielding properties

Electromagnetic shielding (EMI) materials are becoming more and more important because of the increasingly serious radiation pollution. The preparation of high mechanical strength, ultrathin, lightweight, flexible materials with excellent EMI shielding performance have so far been elusive. Here, we try to prepare an ultrathin, lightweight and flexible film with excellent EMI shielding performance using one-dimensional aramid nanofibers (ANFs) and two-dimensional few-layered Ti₃C₂T_x through a simple filtration method. The ultimate tensile strength and strain of the film are up to 116.71 MPa and 2.64%. The EMI shielding effectiveness and the specific EMI shielding efficiency are 34.71 dB and 21971.37 dB cm² g⁻¹, which will be no recession after 1000 times bending. Our results show that a practical EMI shielding material with excellent performances has been successfully prepared, which will be widely applied in wearable electronics, robot joints, and precision instrument protection and so on.     

Toughening effects of titanium dioxide nanoparticles on TiO2/epoxy resin nanocomposites

The purpose of this study was to investigate the influence of adding different volume concentrations of titanium dioxide (TiO₂) nanoparticles to an Araldite LY 564 epoxy resin. In order to characterize the nanoparticles toughening effects, compact tension specimens were used to determine the plane strain fracture toughness (K_IC). Additionally, elastic modulus, tensile strength, and maximum sustained strain were measured in mechanical tensile tests. Composites were analyzed by means of electronic microscopy, both TEM and SEM, to check the dispersion quality of the nanoparticles in thepolymer matrix and to study the observed toughening mechanisms of the fillers. Addition of TiO₂ nanoparticles could simultaneously improve the stiffness and the toughness of the epoxy resin. POLYM. COMPOS., 31:1241–1246, 2010. © 2009 Society of Plastics Engineers     

Transparent,conductive polystyrene in three dimensional configurations

Development of technologies for constructing three-dimensional (i.e. non-planar) transparent conductive electrodes from polymeric materials is a major goal in diverse applications, including optoelectronic devices, flexible electronics, photovoltaics, and others. We present a facile new strategy for creating conductive, transparent gold layering on polystyrene, a widely-used polymer, in different shapes and surface morphologies. The approach is based upon amine functionalization of the polystyrene surface followed by incubation in an aqueous solution of Au(SCN)₄⁻ and brief plasma treatment. We show that this simple deposition process resulted in a homogeneous, transparent, and highly conductive crystalline Au coating. Importantly, electrical conductivity was attained for long distances, even in highly non-planar surfaces containing physical barriers. We further show that the approach can be employed for fabrication of conductive hollow tubes using electrospun polystyrene fibers as templates. The new synthesis scheme might make possible varied applications in polymer-based electronic and photonic devices.     

抗冻水凝胶的制备及其在柔性电子领域的应用

水凝胶具有优异的柔韧性、离子运输性和可调的机械性,在柔性电子领域具有广阔的应用前景,然而,水凝胶电子器件在严寒气候下容易冻结失效,严重限制了其在低温环境下的应用潜力,通过向水凝胶中引入低温防护剂可以赋予水凝胶抗冻性能,拓宽水凝胶电子器件的工作温度。该文从溶质离子、离子液体、有机溶剂以及抗冻蛋白改性水凝胶4个方面,综述了近年来抗冻水凝胶的制备方法和抗冻机理,阐述了抗冻水凝胶在超级电容器、传感器和电池等柔性电子领域的应用进展,归纳了抗冻水凝胶电子材料面临的问题与挑战,并展望了抗冻水凝胶电子材料的发展趋势,指出以天然可再生资源为原料开发具有优异机械性能、电化学性能、生物无毒性、生物相容性和生物可降解的抗冻水凝胶成为下一步研究重点,同时设计优化柔性电子装置、提高器件安全可靠性和输出稳定性也将成为重要的研究方向之一。抗冻水凝胶的制备及其应用研究将促进柔性电子功能材料领域的快速发展。     

抗冻水凝胶的制备及其在柔性电子领域的应用

水凝胶具有优异的柔韧性、离子运输性和可调的机械性,在柔性电子领域具有广阔的应用前景.然而,水凝胶电子器件在严寒气候下容易冻结失效,严重限制了其在低温环境下的应用潜力.向水凝胶中引入低温防护剂可以赋予水凝胶抗冻性能,拓宽水凝胶电子器件的工作温度.该文从溶质离子、离子液体、有机溶剂以及抗冻蛋白改性水凝胶4个方面,综述了近年...     

Preparation of Graphene-Based Hydrogel Thermal Interface Materials with Excellent Heat Dissipation and Mechanical Properties

Heat dissipation has become an essential factor affecting the performance and operating life of electronic devices as the development of modern electronic devices continues to miniaturize and integrate to increase power density. The development of new thermal interface materials has been the key solution to heat dissipation. Herein, a high thermal conductive graphene-based hydrogel (G/PVP-PVA) with an interpenetrating network is successfully constructed by physical cross-linking combined with the freeze–thaw process. The effect of the preparation parameters on its all-around performance is evaluated in detail. When the graphene dosage is 0.33%, the maximal tensile stress of the hydrogel is 322.4 kPa, the self-recovery is 95.4%, and the thermal conductivity is as high as 1.486 W m⁻¹ K⁻¹. The cooling simulation experiment shows that the hydrogel can adhere closely to the wall to reduce the air thermal resistance effectively, and the cooling rate is as high as 5.04 °C min⁻¹. The simulation experiment of the human body cooling shows that its cooling rate is 1.10 °C min⁻¹, while that for a commercial hydrogel is 0.27 °C min⁻¹. The G/PVP-PVA can give a practically potential solution for the thermal management of flexible electronic products and provides a new material for an efficient medical cooling application.     

A self-healing and conductive ionic hydrogel based on polysaccharides for flexible sensors

In this study, we proposed a self-healing conductive hydrogel based on polysaccharides and Li⁺ to serve as flexible sensors. At first, the oxidized sodium alginate(OSA) was obtained through the oxidation reaction of sodium alginate(SA). Then OSA, carboxymethyl chitosan(CMC), and agarose(AGO) were dissolved in Li Cl solution, respectively. Finally, the hydrogel was obtained through heating, mixing, and cooling processes. Because of the Schiff base structure and hydrogen bonding, the hy...     

Highly Stretchable and Sensitive Flexible Strain Sensor Based on Fe NWs/Graphene/PEDOT:PSS with a Porous Structure

With the rapid development of wearable smart electronic products, high-performance wearable flexible strain sensors are urgently needed. In this paper, a flexible strain sensor device with Fe NWs/Graphene/PEDOT:PSS material added under a porous structure was designed and prepared. The effects of adding different sensing materials and a different number of dips with PEDOT:PSS on the device performance were investigated. The experiments show that the flexible strain sensor obtained by using Fe NWs, graphene, and PEDOT:PSS composite is dipped in polyurethane foam once and vacuum dried in turn with a local linearity of 98.8%, and the device was stable up to 3500 times at 80% strain. The high linearity and good stability are based on the three-dimensional network structure of polyurethane foam, combined with the excellent electrical conductivity of Fe NWs, the bridging and passivation effects of graphene, and the stabilization effect of PEDOT:PSS, which force the graphene-coated Fe NWs to adhere to the porous skeleton under the action of PEDOT:PSS to form a stable three-dimensional conductive network. Flexible strain sensor devices can be applied to smart robots and other fields and show broad application prospects in intelligent wearable devices.     

二维导电材料/柔性聚合物复合材料基可穿戴压阻式应变传感器的研究进展

可穿戴应变传感器在人体运动检测、健康监测、可穿戴电子设备和柔性电子皮肤等新兴领域具有极大的应用前景。近年来,由二维（2D）导电材料和柔性聚合物基体组成的可穿戴压阻式应变传感器具有较高的灵敏度、良好的拉伸性和柔韧性、优异的耐久性、可调的应变传感性和易加工等特点,受到广泛关注。基于此,本文对基于2D导电材料/柔性聚合物复合材料（2D-CPC）的可穿戴压阻式应变传感器的类型、传感机理、性能指标、影响因素及应用等进行了综述,并对其未来发展趋势进行了展望。     

双重动态共价键交联纳米纤维素导电水凝胶及其柔性传感器

自愈合导电水凝胶因其良好的自愈合性能与导电性能,在柔性可穿戴设备中具有巨大的应用前景。以4-甲酰基苯硼酸(Bn)交联聚乙烯醇(PVA)和聚乙烯亚胺(PEI)构建基于硼酸酯键和亚胺键的双重动态交联水凝胶网络,引入聚吡咯修饰的纤维素纳米纤维(PPy@CNF)构建了具有良好自愈合和导电性的PBP-PPy@CNF纳米复合水凝胶。结果表明,当PPy@CNF的质量分数为0.8%时,水凝胶的力学性能最佳,其最大应力可达6.65kPa,断裂拉伸应变可达2080%,电导率为2174μS/m。基于该水凝胶的电阻式传感器具有良好的稳定性和重复性,在应变检测范围0～800%内,灵敏因子GF可分为三个线性响应区域,分别是0～200%(GF₁=2.82)、200%～600%(GF₂=7.15)和600%～800%(GF₃=12.85),该传感器能有效检测人体不同部位的运动,可应用于可穿戴传感设备。     

Reversibly highly stretchable and self-healable zwitterion-containing polyelectrolyte hydrogel with high ionic conductivity for high-performance flexible and cold-resistant supercapacitor

It remains challenging to develop stretchable and self-healable polymer electrolytes with improved ion-conductive nature for high-performance multifunctional flexible supercapacitors. Herein, a P(AM-SBMA-AMPS)-SiO₂ zwitterion-containing polyelectrolyte hydrogel is fabricated via copolymerization of acrylamide (AM), sulfobetaine methacrylate (SBMA) zwitterionic monomer, and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) anionic monomer grafted from the surface of vinyl silica nanoparticles (VSNPs). The hydrogen bonding among polymer chains and the high-density dynamic ionic interactions between SBMA and AMPS work as reversible “sacrificial bonds” to toughen hydrogel, while the VSNPs function as multifunctional crosslinkers and stress transfer centers, which makes these hydrogels tough (fracture energy 2.7 MJ m⁻³), stretchable (fracture strain 4,016%), and self-healable (fracture strain of healable sample 775%). More importantly, this zwitterion-containing polyelectrolyte hydrogel exhibits high ionic conductivities (3.4 S m⁻¹) owing to the highly hydration capacity of the zwitterionic polyelectrolyte copolymer which produced efficient ion migration channels for ion transport. Accordingly, a flexible supercapacitor based on this multifunctional hydrogel as electrolyte demonstrates a high electric double-layer capacitive capacitance of 60.6 F g⁻¹ at 0.5 A g⁻¹ and excellent capacitance retention of ~98% over 1,000 cycles as well as encouraging electrochemical properties at subzero temperature. This work provides new insights into the synthesis of highly conductive and multifunctional polyelectrolyte hydrogels for high-performance flexible supercapacitors. © 2020 Wiley Periodicals, Inc.     

Dynamic electro-mechanical analysis of highly conductive particle-elastomer composites

The availability of stretchable conductive materials is a key requirement for the development of soft and wearable electronics. Although there are many promising materials, the characterization of these materials under realistic conditions is complex and a standardized and reliable procedure has not been etablished yet. We therefore introduce a comprehensive protocol for the practice-oriented dynamic electro-mechanical analysis of elastomer-particle composites. In addition to strain dependence (0–100% strain) and fatigue strength (10,000 cycles), this protocol aims in particular to clarify the influence of strain rate (0–100% s⁻¹) on conductivity. Samples with the commonly used filler representatives carbon black and silver flakes with 20 vol% each were prepared and investigated. Silicone elastomers of different stiffness were used as matrix in order to determine its influence. We found that while the conductivity of the carbon black composites of about 1 × 10² S m⁻¹ proved to be fatigue resistant and largely independent of the strain rate, the silver flake composites lost their initially higher conductivity of 1 × 10⁴ S m⁻¹ at high strain rates and increasing numbers of cycles. In addition, the use of a softer silicone matrix improved the performance of both particle composites, which was also demonstrated on an exemplary wearable electronic device.