A novel resistive‐type humidity sensor based on poly(p‐diethynylbenzene)

Poly(p‐diethynylbenzene) (PDEB) synthesized with nickel catalyst Ni(CC ○ CCH)₂(PPh₃)₂ (Ni C) in dioxane–toluene mixed‐solvent system at 25°C shows a rich trans structure with pendant‐group ( ○ CCH) content of about 35% having higher molecular weight and good solubility. A novel resistive‐type humidity sensor based on PDEB is presented. Its humi‐sensing characteristics are described and discussed. The impedance of the sensor changed from ∼ 10³–10⁷ Ω in almost the whole humidity range [∼ 15–92% relative humidity (RH)], which is low compared with sensors based on other humi‐sensitive conjugate polymers, and hysteresis of no more than 3% RH was observed. The sensor prepared by Langmuir–Blodgett (LB) deposition method shows the best humidity response. An explanation of humi‐sensing behavior of PDEB is attempted by taking into account the interaction between hydrogen protons and super π‐conjugate orbits in PDEB. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2010–2015, 1999     

Hyperbranched polycarboxylates and their nanocomposites with ZnO: Investigations on the humidity‐sensitive properties

Hyperbranched polycarboxylates (HBPC) with different alkali metal cations (Li⁺, Na⁺, and K⁺) were prepared and characterized by ¹H‐NMR and thermal gravimetric analysis. Thin film humidity sensors based on HBPC and its composite with ZnO nanorods were fabricated. The morphologies of films of HBPC and the nanocomposite were investigated by atomic force microscopy, which revealed uniform distribution of ZnO nanorods in HBPC. The humidity‐sensitive characteristics of HBPC and the nanocomposite were investigated at room temperature. It was found that the type of cations significantly affected the humidity‐sensing behaviors of HBPC. In addition, the nanocomposite exhibited better humidity‐sensitive properties than HBPC alone. Its impedance decreased for about three orders of magnitude over the range 19–97% RH, showing high sensitivity. Moreover, the nanocomposite exhibited fast response (～ 9 and 10 s for response and recovery time between 97% RH and 33% RH, respectively) and small hysteresis (～ 1.4% RH). The improved humidity‐sensing behaviors of the nanocomposite over HPBC alone is explained by taking into account the hyperbranched structure of the polymer and the special interactions of the polymer and ZnO with water molecules. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Functionalized multi‐wall carbon nanotubes/silicone rubber composite as capacitive humidity sensor

Functionalized multi‐wall carbon nanotubes (MWCNTs) treated by mixed acids have been used to develop a capacitive humidity sensor based on MWCNTs/silicone rubber (SR) composite film. The MWCNTs/SR composites were prepared through conventional solution processed method. The micrographs of MWCNTs/SR composites were observed by transmission electron microscopy (TEM) and scanning electron microscope. The FT‐IR spectra demonstrated the successfully grafting of ? OH groups on the treated MWCNTs. The sensing properties of the composite at different relative humidity (RH) and frequency were characterized and linear sensing responses of the MWCNTs/SR composites to RH were observed. The treated MWCNTs/SR composite film (Tr‐film) had higher sensitivity than that of the untreated MWCNTs/SR composite film (Un‐film). Experimental data indicate that the Tr‐film exhibits an excellent long‐term stability, small hysteresis, and fine reproducibility. The response and recovery time of the Tr‐film were 30 and 27 s, respectively. Thereby, such Tr‐film had potential applications as humidity sensors. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40342.     

Poly(2,3‐dimethylaniline) as a competent material for humidity sensor

Chemically synthesized polyaniline and its ring substituted derivatives such as poly(o‐toluidine), poly(2,3‐dimethylaniline) and poly(2,5‐dimethylaniline) were utilized as sensors for relative humidity (RH) between 6.4% and 97.3%. The conductivity of the polymers was found to decrease on exposure to RH between 6.4% and 75.3%. However, in presence of 97.3% RH the conductivity was seen to increase. A comparison of the observed results reveals that, though each of the polymers responds to various percentages of RH, poly(2,3‐dimethylaniline) shows the best response in terms of sensitivity and linear range. The percent sensitivity was found to be greater for poly(2,3‐dimethylaniline) than that for polyaniline. The observed change in conductivity as well as the degree of change in magnitude of conductivity in the polymers was supported by X‐ray diffraction studies and IR spectroscopy. The X‐ray analysis showed that crystallinity of the polymer changed both in the presence and the absence of a specific percent of RH. Similarly, the IR spectra exhibited variation in the peak intensities of the O—H and >N–H groups. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1382–1387, 2001     

基于电纺NiI2/TPU纳米纤维膜的湿敏变色传感器的制备及性能

以热塑性聚氨酯(TPU)母粒、碘化镍为原料,通过静电纺丝法制备了基于碘化镍/热塑性聚氨酯(NiI2/TPU)纳米纤维膜,将NiI2/TPU纳米纤维膜贴合在聚酰亚胺(PI)基叉指电极上制得湿度传感器.对纳米纤维膜的表面形貌及微观结构进行了表征分析,并研究了该传感器基于颜色变化和电阻电容响应的湿度敏感特性.结果表明,由于碘化镍的颜色变化特性,随相对湿度(RH)从0增加到97％,NiI2/TPU纳米纤维膜显示了从橘红色到黄绿色的颜色转变.此外,该湿度传感器表现出快速的响应/回复时间(0.9 s/9.9 s)、较宽的湿度监测区间(0～97％RH)、较小的洄滞度(0.4％RH)以及优异的稳定性能(>30 d).     

Combination of polymeric substrates and metal–polymer nanocomposites for optical humidity sensors

This paper reports a combination of self-supported, 80-μm-thick polymeric substrates of poly(dimethyl siloxane), poly(methyl methacrylate), poly(vinyl alcohol) (PVA), and poly(N-vinylpyridine) (PVP) and nanocomposites, silver nanoparticle (nAg)/0.1% PVP (S1) and nAg/0.1% PVA (S2), for use in optical-transmission-type humidity sensors. Composites are synthesized by a chemical reduction method at optimum conditions, giving particle sizes of 5–10 nm and 10–20 nm, respectively, for nAg/0.1% PVP and nAg/0.1% PVA. Composite formation is confirmed using Fourier transform infrared spectroscopy (FTIR). The role of polymers in obtaining a smaller Ag particle size is studied using ultraviolet–visible spectroscopy and transmission electron microscopy. The nanocomposite is coated onto substrates either on a single side or on both sides by dip coating. The humidity response of nAg/0.1% PVP-0.1% PVP- nAg/0.1% PVP (S1-PVP-S1) sensors, measured using the direct optical transmission method, exhibits an enhancement in sensitivity [0.88 ± 0.04 (/% RH)] for the humidity range 6–94% RH and response (6 s) and recovery (8 s) times compared to nAg/0.1% PVP-PVP S1-PVP sensors and a linear response (R² ≥ 0.99). An attempt is made to explain the sensing process with the help of FTIR spectra in dry and humid environments. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47035.     

Flexible Humidity and Pressure Sensors Realized by Molding and Inkjet Printing Processes with Sandwich Structure

Flexible and wearable devices are important parts toward the realization of artificial intelligence and have an irreplaceable advantage over traditional rigid sensors. In this work, a film with double surface structure is prepared by using sandpaper and the leather with a rhombic structure as a mold, thereby obtaining a sandwich structure resistive type pressure sensor, which has high sensitivity (77.78 kPa^?1, 24 Pa minimum detection) and wide detection range (0.024–230 kPa). The sensors have fast response time (30 ms) and high reliability over 5000 repetitive cycles. The humidity sensor is printed on the top layer of the sensor by using screen printing and inkjet printing technique, and the sandwich structure humidity and pressure sensor is obtained. The humidity sensors show the sensitivities of 0.137/%, 1.57/%, and 11.145/% in the relative humidity range from 25 to 55%, 55 to 70%, and 70 to 80%, respectively. Such sensors not only have excellent capabilities in pressure and humidity detection, but also avoid the complex process of multiple single‐function devices stacked on each other. The applications of sensors in monitoring artery pulse waves, detecting spatial pressure distribution, and sweat is demonstrated.     

Humidity sensing properties of the vinylpyridine–butyl acrylate–styrene copolymers

In this article, the humidity sensors based on the vinylpyridine (VP)–butyl acrylate (BA)–styrene (St) copolymers are developed. The influencing factors of the copolymer's humidity sensing properties, such as the mol percentage of the fed monomers and the quaternization reagent ratio (namely, dibromobutane : butyl bromide ratio), are studied, and the long‐term stability of the copolymers is investigated as well. The results show that as the content of BA increases and the content of St decreases, the copolymer's hysteresis and response time decreases, and with the increasing of the quaternization reagent ratio, the copolymer's hysteresis and response time decreases. Also, the sensors based on the copolymers show 2–3% RH reproducibility under various long‐term test conditions. These results demonstrate an overall excellent performance in the reproducibility and long‐term stability. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 1992–1996, 1999     

Effect of m‐nitroaniline doping on the optical humidity‐sensing characteristics of cobalt/poly(vinyl alcohol) nanocomposites

Cobalt (Co) nanoparticles (with different loadings, 1 and 2 wt %, of Co) were synthesized in situ in a poly(vinyl alcohol) (PVA) matrix with and without meta‐nitroaniline (m‐NA) as a dopant (2.5 wt %). The obtained nanocomposite films were characterized with various physicochemical techniques, including ultraviolet–visible spectrophotometry, X‐ray diffraction analysis, scanning electron microscopy, and Fourier transform infrared analysis. To study the effect of the humidity, the nanocomposite solutions were coated on planar glass substrates. The beam of an He–Ne laser was incident normal to the film surface and was subjected to variable relative humidities (RHs; 4–93%); the transmitted intensity was measured on a photovoltaic diode. Variations in the intensity of light caused by the changes in RH within the range 3–93% were recorded. We optimized the response by varying the film thickness by coating the solution layer by layer. We generated the RH (4–100%) by passing wet water vapors. The neat PVA film of similar thickness gave humidity sensing in the range 78–93% RH. The sensors with m‐NA‐doped Co/PVA gave better sensitivity (6.4 mV/% RH) than the undoped samples (1.78–2.45 mV/% RH), exhibiting a fast response of 3 s (2–93% RH) and a recovery of 10 s (93 to 2% RH). These samples also showed reversible behavior and long‐term stability (for nearly a year) with a good sensitivity and a large dynamic range (2–95% RH). An attempt was made to explain the results on the basis of a bulk mechanism. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Dielectric and AC conductivity studies of novel porous armalcolite nanocomposite‐based humidity sensor

Armalcolite, a current motivated rare earth ceramic usually available in the moon, had been used for the first time, as dielectric‐type humidity sensors. The armalcolite nanocomposite was prepared using multistep solid‐state sintering under high pressure and a high‐sensitive dielectric sensor was developed for humidity controlling applications. Different concerning phases developed by the proper sintering were analyzed precisely by X‐ray diffraction (XRD) as well as scanning electron microscopy (SEM). At 100 Hz frequency, the obtained dielectric constant was 24 times greater at 95% relative humidity (RH) as compared to 33% RH. The armalcolite‐based sensor showed lower hysteresis (<3.5%), good stability, and faster response (~18 seconds) and recovery (~35 seconds) times compared to conventional humidity sensors. The sensing mechanism of the nanocomposite was categorically determined by the analyzed characteristics parameters such as dielectric constants, normalized loss tangent, and alternating current conductivity properties. This study also confirmed that the whole conduction mechanism was accomplished by electrons or ions and dipoles in the entire RH range. Therefore, the present armalcolite‐based porous nanocomposite would be a potential sensing material for novel humidity sensors.     

Grafting polythiophene on polyethylene surfaces

Polythiophene (PT) was grafted on PE film using three reaction steps. First, PE films were brominated in the gas phase, yielding PE–Br; second, a substitution reaction of PE–Br with 2‐thiophene thiolate anion gave the thiophene‐functionalized PE; finally PT was grafted on the PE surface using chemical oxidative polymerization to give PE–PT. The polymerization was carried out in a suspension solution of anhydrous FeCl₃ in CHCl₃, yielding a reddish PE–PT film after dedoping with ethanol. ATR‐FTIR shows that the PT was grafted on PE in the 2,5‐position. SEM imaging revealed islands of PT on the PE film. AFM analysis found the thickness of islands to be in the range of 120–145 nm. The conductivity of these thin films was in the range of 10^?6 S cm^?1, a significant increase from the value of ～10^?14 S cm^?1 measured for PE film. © 2003 Society of Chemical Industry     

A Novel Highly Sensitive Humidity Sensor Based on ZnO/SBA‐15 Hybrid Nanocomposite

This work deals with the study of hydrothermally synthesized zinc oxide (ZnO) loaded mesoporous SBA‐15 hybrid nanocomposite for relative humidity sensing (RH) at room temperature. The sensor exhibits an excellent ~5 orders impedance change along with excellent linearity, quick response time (17 s), rapid recovery time (18 s), negligible hysteresis (1.2%), good repeatability, and stability (1.8%) in 11%–98% RH range. In addition, complex impedance spectra of the sensor at different RHs were analyzed to understand the humidity sensing mechanism. Our study can open a new way for realizing ZnO/SBA‐15 hybrid nanocomposite for fabrication of high‐performance RH sensors.     

HDPE-AA-SSS预辐照接枝膜的表征及其湿敏性能的研究

采用预辐照法将亲水性单体丙烯酸(AA)和对苯乙烯磺酸钠(SSS)接枝到疏水性高密度聚乙烯(HDPE)薄膜上,制备出新型的接枝膜湿敏元件.通过扫描电镜观测了辐照接枝前和接枝后HDPE膜的表面形貌,并通过红外光谱表征了膜的结构,同时测定了接枝膜湿敏元件的湿敏性能.实验结果表明,制备的接枝膜湿敏元件具有良好的湿敏特性,响应和恢复时间短.它具有较好的稳定性,能在高湿、高温环境下使用.实验结果也表明了接枝HDPE膜具有良好的湿敏性能.     

Synthesis and physicochemical properties of poly[2‐(2‐chloro‐1‐methylbut‐2‐en‐1‐yl)aniline] obtained with various dopants

Highly soluble polyaniline was synthesized from a newly designed aniline derivative, namely 2‐[2‐chloro‐1‐methylbut‐2‐en‐1‐yl]aniline. The corresponding polyanilines, PClPA‐HA, PClPA‐SA, PClPA‐NA and PClPA‐PA, were characterized by means of ¹H NMR, ¹³C NMR, high resolution mass spectroscopy, Fourier transform infrared spectroscopy, ultraviolet–visible spectroscopy and SEM images. The elemental analysis and electrical conductivity of the polymers are also presented. It is shown that the molecular weight of the polymers obtained depends on the method of synthesis. Spectroscopic studies confirmed the emeraldine form of the polyaniline derivatives. In the work, the dependence of the current passing through resistive structures based on thin poly[2‐(2‐chloro‐1‐methylbut‐2‐en‐1‐yl)aniline] films on the relative humidity of air was studied. The results of the studies showed the prospects of using thin polymer films in the design of chemical sensors. © 2020 Society of Chemical Industry     

High performance and moisture stable humidity sensors based on polyvinylidene fluoride nanofibers by improving electric conductivity

Polyvinylidene fluoride (PVDF)‐based nanofiber was successfully produced for a high performance and stable humidity sensor via a solution‐blowing spinning method. The performances of the manufactured sensors, including the impedance change with relative humidity (RH), moisture stability, and response and recovery times, were investigated. To improve charge carrier transfer, which is the main mechanism of humidity sensing, especially under low RH conditions, lithium chloride was used and displayed the best linearity in the impedance change with RH. Fast response and recovery times of 1.7 and 16.1 s were, respectively, achieved with zinc oxide nanoparticles. Furthermore, the sensors showed excellent moisture stability, owing to the hydrophobicity of PVDF, and this was demonstrated via repeatability testing and scanning electron microscopy. The humidity sensing mechanism was discussed using complex impedance spectra. POLYM. ENG. SCI., 59:304–310, 2019. © 2018 Society of Plastics Engineers     

UV‐Printable and Flexible Humidity Sensors Based on Conducting/Insulating Semi‐Interpenetrated Polymer Networks

Humidity sensors are of great interest in many fields because humidity plays a crucial role in several processes. Nevertheless, their application is often limited by the expensive fabrication and the stiffness of the substrates usually employed. In this work, novel UV‐curable and flexible humidity sensors based on semi‐interpenetrated polymer networks are fabricated. They can be prepared either as self‐standing sensors or applied on different bendable substrates. The fabrication consists of a simultaneous UV‐curing of an insulating network (acrylic or epoxy) and photopolymerization of conducting polypyrrole (PPy). The detection mechanism involves proton transfer on the PPy chains that can be macroscopically observed by electrical impedance variations. These devices show promising humidity‐sensing properties from 20 to 97% of relative humidity with a maximum response of about 180%. The dynamic sensing investigation proves that the recovery process can be tailored playing on the glass transition temperature and wettability of the films. The remarkable sensing capabilities of these sensors make them a valid alternative in many applications where printability and flexibility are required along with simple fabrication method consisting of one‐step synthesis.     

Self-doped N-propansulfonic acid polyaniline-polyethylene terephthalate film used as active sensor element for humidity or gas detection

In this work, we report the fabrication of sensors’ element for humidity or gases, prepared by in situ polymerization of aniline N-propansulfonic acid using ammonium persulfate in acidic medium. The polymer is being used in the form of powder or deposited in multiple layers onto the PET film. Various techniques including Fourier Transform infrared (FTIR), ultraviolet-–visible spectroscopy (UV–vis), X-ray diffraction (XRD) and scanning electron microscopy (SEM) were employed to characterize the as-prepared sensing materials. The film has been tested for humidity influence, where the significant variations in electrical characteristics were observed, suggesting its usefulness for humidity sensors. Also, for different organic and inorganic gases, a relatively low operating temperature and important sensitivity were observed that indicate its applicability as an active element for general gases sensors. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47743.     

基于硝化纳米纤维素/琼脂的高灵敏度湿度传感器

湿敏材料是决定湿度传感器性能的关键,本研究将具有特殊化学结构的纤维素和琼脂这两种生物质材料有机结合起来,制备具有不同湿度敏感性的硝化纳米纤维素/琼脂（nitrocellulose nanocrystals/Agar,NCNCs/Agar）复合敏感膜材料,基于石英晶体微天平（quartz crystal microbalance,QCM）制备出具有高灵敏度的湿度传感器。结果表明,NCNCs/Agar复合敏感膜修饰的QCM湿度传感器的灵敏度和频率响应值较单一材料敏感膜修饰的QCM均有较明显的提高。经过优化测试,得到NCNCs与琼脂的最佳质量比为1∶25,涂覆2.049μg敏感材料的QCM传感器（QCM-b）性能最优异。在相对湿度（RH）11%~84%下,QCM-b具有良好的线性（R²=0.9933）,灵敏度为32.54Hz/%RH。在RH 11%~97%下,QCM-b响应值可达到-5820Hz,具有优异的对数拟合系数（R²=0.9994）,恢复时间短（5s）,并且具有良好的重现性和长期稳定性,显示出在湿度探测领域的良好应用前景。     

氧化石墨烯/钒钛酸复合材料的制备及湿敏性能研究

通过Hummers法制备氧化石墨后进行超声分散,得到分散均匀的氧化石墨烯(GO)分散液,物理复合滴涂制备氧化石墨烯/钒钛酸薄膜并对其感湿性能进行了研究,并通过交流与直流方法对其感湿机理进行了深入探究。结果表明:氧化石墨烯/钒钛酸复合膜的湿敏性能优于氧化石墨烯和钒钛酸单层膜,该湿敏薄膜的湿滞为8.3%RH,灵敏度变化2个数量级,响应时间为8 s,还原时间为10 s,曲线线性度良好。材料在低湿阶段主要表现为电子导电,中高湿阶段为电子导电和离子导电同时存在,高湿阶段主要表现为离子导电。     

Polybenzimidazole‐graft‐polyvinylphosphonic acid—proton conducting fuel cell membranes

A new method for the preparation of polybenzimidazole (PBI)‐based membranes, containing high concentrations of immobilized phosphonic acid groups, has been developed. The procedure used is carried out in two steps: (1) Synthesis of modified PBIs, containing 1,2‐dihydroxypropyl groups and preparation of films there from; (2) Introduction of vinylphosphonic acid (VPA) and initiator (cerium ammonium nitrate) in the film, subsequent grafting of VPA from the active sites of the PBI backbone. Membranes with different length of the grafted polyvinylphosphonic acid chains were prepared. The molar ratio grafted VPA units per PBI repeating unit reaches 7.8. Proton conductivity was measured at 120°C and relative humidity (RH) 20–100%. For the membrane with highest concentration of phosphonic acid groups the proton conductivity was 35 mS cm^?1 at 100% RH and 8 mS cm^?1 at 20% RH. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013