Flexible polydimethylsiloxane pressure sensor with micro-pyramid structures and embedded silver nanowires:A novel application in urinary flow measurement

Flexible pressure sensors are lightweight and highly sensitive,making them suitable for use in small portable devices to achieve precise measurements of tiny forces.This article introduces a low-cost and easy-fabrication strategy for piezoresistiveflexible pressure sensors.By embedding silver nanowires into a polydimethylsiloxane layer with micro-pyramids on its surface,aflexible pressure sensor is created that can detect low pressure(17.3 Pa)with fast response ms)and high sensitivity(69.6 mA(<20 kPa-1).Furthermore,the pressure sensor exhibits a sensitive and stable response to a small amount of waterflowing on its surface.On this basis,theflexible pressure sensor is innovatively combined with a micro-rotor to fabricate a novel urinaryflow-rate meter(uroflowmeter),and results from a simulated human urination experiment show that the uroflowmeter accurately captured all the essential shape characteristics that were present in the pump-simulated urination curves.Looking ahead,this research provides a new reference for usingflexible pressure sensors in urinaryflow-rate monitoring.

巯基改性AgNWs用于提升AgNWs/聚乙烯醇/硼砂水凝胶电导率

银纳米线(AgNWs)有着优异的导电性、可弯曲性和较大的长径比等性能,广泛应用在柔性电子器件领域。然而,银纳米线之间高的接触电阻和在基体中较差的分散性会极大地降低其导电网络地电导率。首先通过多元醇法成功合成了AgNWs,其平均长度为79.44μm,平均直径为102.29 nm。然后利用S跟Ag之间地强配位作用,采用含有-SH和-OH的改性剂对AgNWs表面进行改性,研究其在水凝胶中的分散性以及对水凝胶电导率的贡献。研究结果表明,采用硫代甘油(MPD)改性剂对AgNWs改性的效果最佳。当MPD的乙醇分散液(5 mM)与AgNWs的乙醇分散液(2 mg/m L)体积比为1∶1时,改性剂在AgNWs表面分布相对均匀,没有出现大面积的团聚现象。将改性的AgNWs加入到聚乙烯醇(PVA)/硼砂水凝胶中,当添加量为0.04%时,水凝胶电导率为0.858 S/m,相比于未改性AgNWs的PVA/硼砂水凝胶电导率提高了94%。

长径比大于1200的超长AgNWs制备及影响因素

采用改进多元醇法制备了长径比大于1200的超长银纳米线(AgNWs)。系统研究了反应温度(120~170℃)、反应时间(0.5~3h)、搅拌速率(0~300rpm)、聚乙烯吡咯烷酮(PVP)分子量(58000~1280000 g/mol)、氯化铁(FeCl_(3))乙二醇溶液添加量(0~5.6 g,5 mM)和PVP添加量(0.2~1 g)对AgNWs形貌的影响。在最佳实验条件下,制备的超长Ag NWs平均长度约96.6μm,平均直径约80.0 nm。此外,通过简单的调控PVP添加量可以获得不同长度和直径的Ag NWs。

Fluxless bonding with silver nanowires aerogel in die-attached interconnection

The electronic product has gravitated towards component miniaturization and integration, employment of lead-free materials, and low-temperature soldering processes. Noble-metal aerogels have drawn increasing attention for high conduction and low density. However,the noble metal aerogels with outstanding solderability were rarely studied. This work has successfully synthesized an aerogel derived from silver nanowires(AgNWs) using a liquid phase reduction method. It is found that the noble metal aerogels can be made into diverse aerogel preformed soldering sheets. The influence of bonding temperature(150-300 ℃), time(2-20 min), and pressure(5-20 MPa) on the joint strength of the AgNWs aerogel affixed to electroless nickel/silver copper plates were investigated. Additionally, the AgNWs aerogel displays almost the same shear strength for substrates of various sizes. In a word, this study presents a flux-free, high-strength, and adaptable soldering structural material.

Bifunctional flexible electrochromic energy storage devices based on silver nanowire flexible transparent electrodes

Flexible electrochromic energy storage devices(FECESDs)for powering flexible electronics have attracted considerable attention.Silver nanowires(AgNWs)are one kind of the most promising flexible transparent electrodes(FTEs)materials for the emerging flexible devices.Currently,fabricating FECESD based on AgNWs FTEs is still hindered by their intrinsic poor electrochemical stability.To address this issue,a hybrid AgNWs/Co(OH)_(2)/PEDOT:PSS electrode is proposed.The PEDOT:PSS could not only improve the resistance against electrochemical corrosion of AgNWs,but also work as functional layer to realize the color-changing and energy storage properties.Moreover,the Co(OH)_(2)interlayer further improved the color-changing and energy storage performance.Based on the improvement,we assembled the symmetrical FECESDs.Under the same condition,the areal capacitance(0.8 mF cm^(−2))and coloration efficiency(269.80 cm^(2)C−1)of AgNWs/Co(OH)_(2)/PEDOT:PSS FECESDs were obviously higher than AgNWs/PEDOT:PSS FECESDs.Furthermore,the obtained FECESDs exhibited excellent stability against the mechanical deformation.The areal capacitance remained stable during 1000 times cyclic bending with a 25 mm curvature radius.These results demonstrated the broad application potential of the AgNWs/Co(OH)_(2)/PEDOT:PSS FECESD for the emerging portable and multifunctional electronics.

PVDF@AgNWs复合压电发电机的制备与性能研究

采用静电纺丝法和退火后处理工艺制备高β相含量的聚偏氟乙烯(PVDF)纤维膜,并通过复合银纳米线(AgNWs)形成导电网络来获得高性能PVDF@AgNWs压电发电机。研究了制备工艺(静电纺丝、退火)及AgNWs添加量对器件压电输出性能的影响,结果表明,电纺PVDF纤维膜经退火并控制AgNWs质量分数0.10%条件下,PVDF@AgNWs压电发电机在5 MPa压力下,可输出约114 V压电电压及约1.3×10-7 A电流。该压电发电机具有良好的能量采集性能,可直接为电容器充电,并可驱动LCD显示模组,在自供电柔性可穿戴电子领域具有应用潜力。

Plasmon-enhanced nanosoldering of silver nanoparticles for high-conductive nanowires electrodes

The silver nanowires(Ag NWs)electrodes,which consist of incompact Ag nanoparticles(NPs)formed by multi-photon photoreduction,usually have poor conductivities.An effective strategy for enhancing conductivity of the Ag NWs elec-trodes is plasmon-enhanced nanosoldering(PLNS)by laser irradiation.Here,plasmon-enhanced photothermal effect is used to locally solder Ag NPs and then aggregates of these NPs grow into large irregular particles in PLNS process.Fi-nite element method(FEM)simulations indicate that the soldering process is triggered by localized surface plasmon-in-duced electric field enhancement at“hot-spots”.The effectiveness of PLNS for enhancing conductivity depends on laser power density and irradiation time.By optimizing the conditions of PLNS,the electrical conductivity of Ag NWs is signific-antly enhanced and the conductivityσs is increased to 2.45×107 S/m,which is about 39%of the bulk Ag.This PLNS of Ag NWs provides an efficient and cost-effective technique to rapidly produce large-area metal nanowire electrodes and capacitors with high conductivity,excellent uniformity,and good flexibility.

Controlled growth of large＇scale silver nanowires

Large-scale silver nanowires with controlled aspect ratio were synthesized via reducing silver nitrate with 1, 2- propanediol in the presence of poly （vinyl pyrrolidone） （PVP）. Scanning electron microscopy, transmission electron microscopy and x-ray powder diffraction were employed to characterize these silver nanowires. The diameter of the silver nanowires can be readily controlled in the range of 100 to 400 nm by varying the experimental conditions. X-ray photoelectron spectroscopy and Fourier transform infrared spectroscopy results show that there exists no chemical bond between the silver and the nitrogen atoms. The interaction between PVP and silver nanowires is mainly through the oxygen atom in the carbonyl group.

Precise assembly and joining of silver nanowires in three dimensions for highly conductive composite structures

Three-dimensional(3D)electrically conductive micro/nanostructures are now a key component in a broad range of research and industry fields.In this work,a novel method is developed to realize metallic 3D micro/nanostructures with silver-thiol-acrylate composites via two-photon polymerization followed by femtosecond laser nanojoining.Complex 3D micro/nanoscale conductive structures have been successfully fabricated with∼200 nm resolution.The loading of silver nanowires(AgNWs)and joining of junctions successfully enhance the electrical conductivity of the composites from insulating to 92.9 Sm^−1 at room temperature.Moreover,for the first time,a reversible switching to a higher conductivity is observed,up to∼10^5Sm^−1 at 523 K.The temperature-dependent conductivity of the composite is analyzed following the variable range hopping and thermal activation models.The nanomaterial assembly and joining method demonstrated in this study pave a way towards a wide range of device applications,including 3D electronics,sensors,memristors,micro/nanoelectromechanical systems,and biomedical devices,etc.

Silver Nanowires Contained Nanofluids with Enhanced Optical Absorption and Thermal Transportation Properties

Two kinds of silver nanowires(100 nm in diameter, 20 μm and 100 μm in length) are prepared. The thermo-physical characteristics, viscosity, and photothermal conversion performance of the silver nanowires(AgNWs)contained ethylene glycol nanofluids are investigated in detail. It is found that thermal conductivity of 100 μm AgNWs contained nanofluids is higher than that of 20 μm AgNWs with the same diameters of 100 nm. Viscosity test shows that the nanofluid is a Newtonian fluid, and the longer silver nanowires, the greater viscosity. In addition, photothermal conversion efficiency of silver nanowires contained nanofluid is studied. We can observe that the 100 μm AgNWs contained nanofluid has a higher photothermal conversion efficiency than that containing 20 μm AgNWs. Moreover, we find that there is a certain correlation between heat transfer and photothermal conversion of nanofluid. It demonstrates that the high heat transfer property of nanofluid will benefit for its photothermal conversion efficiency and the mechanism is proposed. This work provides a new idea to improve photothermal conversion efficiency. We can choose materials with high thermal conductivity and strong light absorption ability to enhance the photothermal conversion performance of nanofluids.

Efficiency-enhanced AlGaInP light-emitting diodes using transparent plasmonic silver nanowires

Silver nanowire（AgNW） networks have been demonstrated to exhibit superior transparent and conductive performance over that of indium-doped tin oxide（ITO） and have been proposed to replace ITO, which is currently widely used in optoelectronic devices despite the scarcity of indium on Earth. In this paper, the current spreading and enhanced transmittance induced by AgNWs, which are two important factors influencing the light output power, were analyzed. The enhanced transmittance was studied by finite-difference time-domain simulation and verified by cathodoluminescence measurements.The enhancement ratio of the light output power decreased as the Ga P layer thickness increased, with enhancement ratio values of 79%, 52%, and 15% for Ga P layer thicknesses of 0.5 μm, 1 μm, and 8 μm, respectively, when an AgNW network was included in Al Ga In P light-emitting diodes. This was because of the decreased current distribution tunability of the AgNW network with the increase of the Ga P layer thickness. The large enhancement of the light output power was caused by the AgNWs increasing carrier spread out of the electrode and the enhanced transmittance induced by the plasmonic AgNWs. Further decreasing the sheet resistance of AgNW networks could raise their light output power enhancement ratio.

Effect of a Magnetic Field on the Preparation of Silver Nanowires Using Solid Electrolyte Thin Films

The effect of an external magnetic field on the preparation of silver nanowires was studied. The silver nanowires were synthesized using solid electrolyte RbAg4I5 thin films by applying both a direct current （DC） electric field and a magnetic field. The RbAg4I5 thin films, which were prepared by deposition at room temperature and atmospheric pressure on a NaCI substrate, were used for the transfer of Ag^＋ ions between two Ag electrodes during the preparation process. When only the DC electric field is applied, the silver ions migrate toward the cathode. On the edge of the silver film at the cathode the Ag^＋ ions congregate to form aligned nanowires. If the magnetic field is also applied perpendicular to the DC electric field, the morphology of the nanowires can be controlled by rotating the sample in the magnetic field. Experimental results show that the growth of the silver nanowires is determined by the Ag^＋ ionic flux.

Rational Synthesis of Cylindrical Silver Single-crystalline Nanowires via Poly(vinyl pyrrolidone) Reduction of AgCl

We presented a simple yet convenient hydrothermal approach for the large-scale synthesis of uniform cylindrical silver (Ag) single-crystalline nanowires with diameters of about 25 nm and lengths of 1-4 μm. Poly(vinyl pyrrolidone) (PVP) was used as a reducing agent, and AgCl was used as a precursor to deliberately control [Ag^+] at a low degree in the overall reaction process through its dynamic equilibrium by directly reducing AgCl with PVP at a quasi-equilibrium growth condition. The as-obtained products were characterized by powder X-ray diffraction (XRD) patterns, field emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), infrared spectra (IR) and Raman spectra. Factors such as [PVP], reaction temperature, time, and species of reducing agents and precursors were investigated to have strong influences on the morphologies and structures of the resultant Ag nanostructures. The wire diameter can conveniently be adjusted between 25 and 50 nm by simply adjusting [PVP], reaction temperature and reducing agent species. The as-synthesized silver nanowires can be self-assembled into perfect order arrays after being dried on tin foil due to the PVP coating on the surface, the circular cross-section and the uniform diameter of the Ag nanowires. These special silver nanowires with a core-shell structure as well as their spontaneous self-assembly of order arrays are expected to provide potential applications in flexible conductors, dielectric materials, electromagnetic shielding materials and nano-devices.

Fabrication of High-Haze Flexible Transparent Conductive PMMA Films Embedded with Silver Nanowires

High-haze flexible transparent conductive polymethyl methacrylate （PMMA） films embedded with silver nanowires （AgNWs） are fabricated by a low-cost and simple process. The volatilization rate of the solvent in PMMA solution affects the surface microstructures and morphologies, which results in different haze factors of the composite films. The areal mass density of AgNW shows a significant influence on the optical and electrical properties of composite films. The AgNW/PMMA transparent conductive films with the sheet resistance of 5.5Ω sq ^-1 exhibit an excellent performance with a high haze factor of 81.0% at 550？nm.

Stretchable and self-healing conductive fibers from hierarchical silver nanowires-assembled network

Conductive fibers(CFs)with features of high conductivity,stretchability,self-healability,and electromechanical stability are key components of the increasingly popular wearable electronics.However,since the lack of structural design of conductive network and interfacial interaction between soft polymer and conductive additives,it is still hard to enable CFs to meet above requirements.Here,we describe a facial drawing method from a hydrogel reservoir which is remolded into ultrathin and stretchable CFs with excellent multi-responsive self-healability.The hydrogel reservoir was fabricated in synergy of an ice-templating method and in situ polymerization using the assembled framework as a crosslinker.Relying on the effective fabrication mechanism,the diameter of CFs could be well-tuned from 90 to 400μm by adjusting the dipping depth of the glass rod,accompanied with conductivity increased from 0.75 to 2.5 S/m.Since the hierarchical network structure was well maintained in the CFs,professional performances have been proved on the stretchability and electromechanical stability.The presence of massive hydrogen bonding and Ag–S bond enabled the CFs with excellent self-healability under the conditions of contact,electric field,and near infrared light,respectively.Excitingly,the CFs with high sensing property could be integrated into an advanced textile sensor through an effective healing-induced integration strategy,demonstrating its great potentials as superior two-dimensional(2D)electronic skins.

AgNWs@SiO_(2)/PI复合薄膜制备及性能研究

为了提高聚酰亚胺薄膜热导率的同时维持绝缘性,采用SiO_(2)对AgNWs进行表面绝缘包覆获得AgNWs@SiO_(2)核壳结构,首先通过静电纺丝技术将AgNWs@SiO_(2)分散在聚酰胺酸(PAA)电纺纤维内部,规划导热路径,同时改善AgNWs@SiO_(2)在PI基体中的分散性,再用含AgNWs@SiO_(2)的PAA胶液浸渍PAA电纺膜,热亚胺化后得到E-AgNWs@SiO_(2)/PI复合薄膜。研究其填料改性和含量对复合薄膜导热性能和绝缘性能的影响。结果表明:当填料质量分数为25%时,E-AgNWs/PI和E-AgNWs@SiO_(2)/PI复合薄膜的热导率分别为2.92 W/(m·K)和2.80 W/(m·K),分别是纯PI薄膜的14.6倍和14倍。E-AgNWs@SiO_(2)/PI复合薄膜的介电常数降低至5以下,并且介质损耗因数维持在0.015以下,体积电阻率提升至1.79×10^(13)Ω·m。

PVDF基BNNs@AgNWs复合导热网络的构建及性能研究

利用溶剂法将氮化硼(BN)剥离成氮化硼纳米片(BNNs),使其表面含有大量羟基,再利用原位还原生成氮化硼纳米片与银纳米线复合填料(BNNs@ AgNWs)。经过与聚偏氟乙烯(PVDF)共混热压制得具有三维导热网络结构的PVDF/BNNs@ AgNWs复合材料。分别采用傅立叶红外光谱仪(FTIR)、透射电子显微镜(TEM)、扫描电子显微镜(SEM)、X射线多晶体衍射仪(XRD)和X射线光电子能谱仪(XPS)等方法表征该复合填料的形貌与结构。利用FTIR验证了BNNs上含有羟基,且有利于AgNWs的生成,更可以有效降低界面热阻。XRD、TEM和XPS更进一步验证了复合填料的成功制备。对添加不同含量填料的复合材料力学性能和热导率的研究表明,在含量为5%时,复合材料的力学性能最佳。在高的长径比AgNWs的作用下构筑的三维导热网络,使得填料含量为20%时,复合材料热导率达到0.645 W/(m·K)。

AgNWs柔性传感器模板法制备与性能分析

基于银纳米线(AgNWs)优良的导电性、优异的透光性、耐曲挠性等特点,制备了高长径比的AgNWs;利用模板法将AgNWs材料和聚二甲基硅氧烷(PDMS)结合,制备了柔性薄膜应力传感器。通过对该传感器的性能测试与结果分析,得到其最大应变系数为517.24;通过按压和脉搏测试实验证明:制备的柔性应力传感器可用于微小应力检测,电子皮肤、生命体征检测等领域。

新型AgNWs/PVDF电磁屏蔽材料的制备及性能研究

采用改进的多元醇水热法制备银纳米线(AgNWs),并以PVDF为基体采用溶液析出共混和热压技术制备AgNWs/PVDF复合材料。利用扫描电子显微镜对AgNWs的形貌和复合材料断面进行表征,发现AgNWs在复合材料中分布均匀。采用阻抗分析仪和四探针测试仪对复合材料的交流电导率和直流电导率进行测试,银纳米线含量越高,AgNWs/PVDF复合材料的电导率也越高,当AgNWs含量为5%(质量分数)时,复合材料电导率就可以到达0.56 S/cm。采用矢量网络分析仪对复合材料的电磁屏蔽性能进行测试,当AgNWs为5%(质量分数)时,复合材料的电磁屏蔽性能到达28 dB,并且随着AgNWs含量的增加,复合材料电磁屏蔽性能也随着提高。

Silver Nanowire Electrodes: Conductivity Improvement Without Post-treatment and Application in Capacitive Pressure Sensors

Transparent electrode based on silver nanowires(Ag NWs) emerges as an outstanding alternative of indium tin oxide film especially for flexible electronics. However, the conductivity of Ag NWs transparent electrode is still dramatically limited by the contact resistance between nanowires at high transmittance. Polyvinylpyrrolidone(PVP) layer adsorbed on the nanowire surface acts as an electrically insulating barrier at wire–wire junctions, and some devastating post-treatment methods are proposed to reduce or eliminate PVP layer, which usually limit the application of the substrates susceptible to heat or pressure and burden the fabrication with high-cost, time-consuming, or inefficient processes. In this work, a simple and rapid pre-treatment washing method was proposed to reduce the thickness of PVP layer from 13.19 to0.96 nm and improve the contact between wires. Ag NW electrodes with sheet resistances of 15.6 and 204 X sq-1have been achieved at transmittances of 90 and 97.5 %, respectively. This method avoided any post-treatments and popularized the application of high-performance Ag NW transparent electrode on more substrates. The improved Ag NWs were successfully employed in a capacitive pressure sensor with high transparency, sensitivity, and reproducibility.