Gas sensing properties of a composite composed of electrospun poly(methyl methacrylate) nanofibers and in situ polymerized polyaniline

Poly(methyl methacrylate) (PMMA) nanofibers with different diameters were fabricated by electrospinning and their composites with polyaniline (PANI) were formed by virtue of in situ solution polymerization. The coaxial composite nanofibers so prepared were then transferred to the surface of a gold interdigitated electrode to construct a gas sensor. The structure and morphology of the PANI/PMMA composite fibers were characterized by UV–vis spectroscopy and scanning electron microscopy, which indicated that the coaxial nanofibres of PANI emeraldine salt and PMMA were successfully prepared. The electrical responses of the gas sensor based on the composite nanofibres towards triethylamine (TEA) vapors were investigated at room temperature. It was revealed that the sensor showed a sensing magnitude as high as 77 towards TEA vapor of 500 ppm. In addition, the responses were linear, reversible and reproducible towards TEA vapors ranging from 20 to 500 ppm. The diameters of the electrospun PMMA fibers had an effect on the sensing magnitude of the gas sensor, which is proposed to relate to the difference in the surface-to-volume ratio of the fibers. Furthermore, it was found that the concentration of doping acids only led to changes in resistance of the sensor, but could not affect its sensing characteristics. In contrast, the nature of the doping acids was determinative for the sensing magnitude of the sensor. The gas sensor with toluene sulfonic acid as the doping acid exhibited the highest sensing magnitude, which is explained by taking into account of the sensing mechanism and the interactions of doping acids with TEA vapor.     

Application of sulfuric acid doped poly (m-aminophenol) as aliphatic alcohol vapor sensor material

Chemically synthesized processable poly (m-aminophenol) (PmAP) film was cast from dimethyl sulfoxide solution and doped with sulfuric acid by solution doping technique. This sulfuric acid doped PmAP film shows a good electrical conductivity. The response of doped film under continuous flow of various aliphatic alcohols vapor and air mixture was examined at room temperature (30 °C) and humidity (65% RH). The doped polymer only showed good result for methanol and ethanol vapor and some week response for the isopropanol vapor. A decrease in resistivity of the doped PmAP film was separately observed in air–alcohol vapor at different concentrations. The response of the film increases as the concentration of the alcohol vapor increases in air–alcohols vapor mixture. The kinetics of the response with respect to the alcohol concentration was studied for methanol and ethanol. Sulfuric acid doped and methanol vapor absorbed doped films were characterized by ultraviolet–visible spectroscopic, attenuated total reflectance Fourier transformed infrared spectroscopic and X-ray diffraction analyses. The mechanism of alcohol vapor sensing by sulfuric acid doped PmAP film has been explained on the basis of the above characterizations. All the above facts are trying to explain from the proposed mechanistic point of view.     

Gas sensing properties of a clad modified fiber optic sensor with Ce, Li and Al doped nanocrystalline zinc oxides

Spectral characteristics of a clad modified fiber optic gas sensor are studied for various concentrations (0-500 ppm) of ammonia, methanol and ethanol at room temperature. Cerium, aluminum and lithium doped (6 at.%) nanocrystalline zinc oxides are replaced with a clad and used as gas sensing materials. The study shows that the spectral intensity increases linearly with concentration for ammonia whereas it decreases for methanol and ethanol. The Ce doped ZnO exhibits higher gas sensitivity compared to Al and Li doped zinc oxides. The time response of the sensor is presented for a Ce doped ZnO with ammonia gas. A model is proposed for understanding the spectral intensity variations.     

Simultaneous strain and temperature measurements in composites using extrinsic Fabry–Perot interferometric and intrinsic rare-earth doped fiber sensors

This paper reports on a novel optical fiber-based sensing system for conducting simultaneous strain and temperature measurements. The sensor design involves the use for the first time of an extrinsic Fabry–Perot interferometric (EFPI) strain sensor in conjunction with a rare-earth doped fiber fluorescence decay-time based temperature sensor. The combined sensors were embedded in a carbon fiber reinforced composite system and evaluated. The feasibility of using this type of embedded sensor configuration for simultaneous strain and temperature measurements was demonstrated.     

基于电镀技术的微间隔制作及在气体检测中应用的研究

本文开发了一种基于电离现象的气体传感器。文章首先研究了采用低成本的电镀方法来制作具有微米间隔的镍电极对,然后通过测试在不同条件下电极对的击穿电压和电流来实现气体检测。实验结果表明该器件对乙醇气体,其击穿电压在300 V左右;而对水蒸气,其击穿电压在320 V左右。同时,对乙醇而言,随着乙醇浓度的增加,在同一击穿电压下击穿电流也不断增大。对不同浓度的水蒸气的实验中也得到相类似的结果。     

基于电镀技术的微间隔制作及其在气体检测中应用的研究

开发了一种基于电离现象的气体传感器。首先研究了采用低成本的电镀方法来制作具有微米间隔的镍电极对,然后通过测试在不同条件下电极对的击穿电压和电流来实现气体检测。实验结果表明该器件对乙醇气体,其击穿电压在300 V左右;而对水蒸气,其击穿电压在320 V左右。同时,对乙醇而言,随着乙醇浓度的增加,在同一击穿电压下击穿电流也不断增大。对不同浓度的水蒸气的实验中也得到相类似的结果。     

Composites of carboxylate-capped TiO2 nanoparticles and carbon black as chemiresistive vapor sensors

Titanium (IV) dioxide (TiO₂) nanoparticles (NPs) with a 1-5 nm diameter were synthesized by a sol-gel method, functionalized with carboxylate ligands, and combined with carbon black (CB) to produce chemiresistive chemical vapor sensor films. The TiO₂ acted as an inorganic support phase for the swellable, organic capping groups of the NPs, and the CB imparted electrical conductivity to the film. Such sensor composite films exhibited a reproducible, reversible change in relative differential resistance upon exposure to a series of organic test vapors. The response of such chemiresistive composites was comparable to, but generally somewhat smaller than, that of thiol-capped Au NPs. For a given analyte, the resistance response and signal-to-noise ratio of the capped TiO₂-NP/CB composites varied with the identity of the capping ligand. Hence, an array of TiO₂-NP/CB composites, with each film having a compositionally different carboxylate capping ligand, provided good vapor discrimination and quantification when exposed to a series of organic vapors. Principal components analysis of the relative differential resistance response of the sensor array revealed a clear clustering of the response for each analyte tested. This approach expands the options for composite-based chemiresistive vapor sensing, from use of organic monomeric or polymeric sorbent phases, to use of electrically insulating capped inorganic NPs as the nonconductive phase of chemiresistive composite vapor sensors.     

Recent developments in novel silica-based optical fibers

We have summarized our recent work in the area of novel silica-based optical fibers, which can be classified into two types: silica optical fiber doped with special elements including Bi, Al, and Ce, and micro-structured multi-core fibers. For element-doped optical fiber, the Bi/Al co-doped silica fibers could exhibit a fluorescence spectrum covering the wavelength range between 1000 and 1400 nm with a full width at half maximum (FWHM) of about 150 nm, which enables its use in fiber amplifiers and laser systems. The Ce-doped fiber’s center wavelengths of excitation and emission are about 340 and 430 nm, respectively. The sapphire-derived fiber (SDF) with high alumina dopant concentration in the core can form mullite through heating and cooling with arc-discharge treatment. This SDF can be further developed for an intrinsic Fabry-Perot interferometric that can withstand 1200 °C, which allows it to be used in high-temperature sensing applications. Owing to the strong evanescent field, micro-structured multi-core fiber can be used in a wide range of applications in biological fiber optic sensing, chemical measurement, and interference-related devices. Coaxial-core optical fiber is another novel kind of silica-based optical fiber that has two coaxial waveguide cores and can be used for optical trapping and micro-particle manipulation by generating a highly focused conical optical field. The recent developments of these novel fibers are discussed.

     

镍镧复合氧化物的掺杂及其气敏性能研究

用共沉淀法制备了镍镧复合氧化物并对其进行三价、四价离子系列掺杂。研究了掺杂物的气敏性能。实验结果表明,SiO2,TiO2,SnO2,Al2O3,SbCl3等掺杂的复合氧化物,均对乙醇有较高的气敏性,而对汽油、H2及LPG等气敏性较低。其中TiO2掺杂量为4%(摩尔分数)的镍镧复合氧化物对乙醇的气敏性能最好。探讨了Si,Ti,Sn,Al,Sb等离子的价态,离子半径及复合氧化物的形成条件等与气敏性能的关系,研究了工作温度,被测气体浓度对元件气敏性能及对气体选择性的影响。     

Humidity sensing and electrical properties of a composite material of nano-sized SiO2 and poly(2-acrylamido-2-methylpropane sulfonate)

A composite material of nano-sized SiO₂ and poly(2-acrylamido-2-methylpropane sulfonate) (poly(AMPS)) was used to make a humidity sensor. The infrared (IR) spectra and microstructure of the material were analyzed, and the humidity sensing and electrical properties of the sensor were measured. The sensor well responded to humidity with a relative good linearity, though it depended on the applied frequency. The temperature influence between 15 and 35 °C was −0.71 and −0.15% RH/°C at 30 and 90% RH, respectively. The sensor showed a negligible hysteresis and fast response time upon humidification and desiccation. The stability of the sensor in a highly humid and alcoholic environment increased with increasing the SiO₂ content. The activation energy for conduction reduced with water adsorption. The different impedance plots observed at low and high relative humidity suggested different sensing mechanisms of the SiO₂/poly(AMPS) composite material.     

基于聚合物碳黑混合物气敏微传感器的研究

通过四种不同的聚合物敏感材料以及混合的碳黑修饰在梳状微电极上,可以得到这种新型的化学气敏电阻型微传感器,将这四种不同聚合物的微传感器分别对丙酮、乙醇、甲醇、甲苯四种有机类气体进行了测试,比较其电阻的相对变化率,利用其响应的主元分析可以将四种气体区分开,并且在一定范围内,电阻的相对变化率可呈一定的线性分布.     

The application of a light guiding flexible tubular waveguide in evanescent wave absorption optical sensing

A light guiding flexible fused silica (FFS) capillary has been used in designing evanescent wave (EW) absorption based chemical sensors. The FFS capillary is similar to a conventional silica optical fiber in that it can guide light in the wavelength region from UV to near infrared, but different from a conventional optical fiber in that it is a tubular waveguide. The inner surface of the FFS capillary is fused silica, which was coated with a reagent doped polymer in order to design an optical fiber chemical sensor. The FFS capillary has a cladding layer plus a protection polymer coating on its outside surface. The cladding layer ensured the capability of the FFS capillary for guiding light. The protection coating increases the FFS capillary's mechanical strength and makes it robust in practical applications. This makes the FFS capillary very useful in designing an EW based optical chemical sensor of a long path length. Techniques for activating the inner surface of an FFS capillary, coating the inner surface of the capillary with a polymer, connecting the coated capillary to a light source and a photodetector, and delivering a sample through the capillary have been developed in this work. Three optical sensors for sensing Cu(II), toluene in water samples and ammonia in a gas sample have been fabricated and tested. Preliminary test results obtained in this work illustrate the feasibility of fabricating highly sensitive EW absorption based chemical sensors with the light guiding FFS capillary.     

室温固相化学反应法合成CdSnO3纳米粉及其铂、钯掺杂物气敏特性研究

用室温固相化学反应法合成了CdSnO3纳米粉,以XRD、SEM、Raman光谱等检测手段对其形貌和微观结构进行了表征,并进一步以铂、钯等贵金属对其进行掺杂,研究了它们的气敏性能.实验证明室温固相法合成的CdSnO3具有粒径大小均匀、纯度高、比表面积大等特点;掺杂铂、钯等贵金属后,灵敏度和选择性都有很大提高,对汽油、液化石油气、甲烷、一氧化碳、丁烷等的抗干扰能力强,且稳定性好,可望开发为一种性能优良的酒敏传感器.     

Vapor sensing properties of thermoplastic polyurethane multifilament covered with carbon nanotube networks

The volatile organic compound (VOC) vapor sensing properties of a novel kind of thermoplastic polyurethane multifilament - carbon nanotubes (TPU-CNTs) composites is studied. And the sensing is based on changes in the electrical resistance of the composites due to vapor contact. The composites were readily obtained by adhering CNTs on the surface layer of TPU by means of simply immersing pure TPU multifilament into CNT dispersion. The uniformly formed nanotube networks on the outer layer of composite multifilament are favorable for providing efficient conductive pathways. The resulting TPU-CNTs composites show good reproducibility and fast response (within seconds) of electrical resistance change in cyclic exposure to diluted VOC and pure dry air. The vapor sensing behaviors of the composites are related to CNT content, vapor concentration, and polar solubility parameters of the target vapors. A relatively low vapor concentration of 0.5% is detectable, and a maximum relative resistance change of 900% is obtained for the composite with 0.8 wt.% CNT loading when sensing 7.0% chloroform. It is proposed that both the disconnection of CNT networks caused by swelling effects of the TPU matrix and the adsorption of VOC molecules on the CNTs are responsible for the vapor sensing behavior of TPU-CNTs composite, while the former effect plays the major role.     

基于拉曼放大和掺铒光纤激光器的远程无源传感系统

提出了一种包含拉曼放大和掺铒光纤激光器的远程无源传感系统。该系统中拉曼放大的剩余泵浦功率可用作掺铒光纤激光器的泵浦源,产生的激光信号作为传感信号省略了额外的传感光源。由于拉曼放大作用,可以实现75km长距离无源传感而获得超过40dB的高信噪比。     

Ionic liquids used as QCM coating materials for the detection of alcohols

Six imidazolium-based ionic liquids (ILs) were synthesized and employed as sensing materials coated on quartz crystal microbalance for the detection of organic vapors. Acetone, ethanol, dichloromethane, benzene, toluene and hexane were selected as representatives for common environmental pollutants, and good linear responses from 0 to 100% of concentrations were observed. The halogen-anion-containing imidazolium ILs-coated sensors showed fast response, excellent reversibility, and considerable sensitivity and selectivity towards alcohols, and the selective factors were up to 30 times for ethanol versus other VOCs. The existence of water vapor reduced the frequency response of the sensor, but a good linear relationship remained.     

长周期光纤光栅化学传感器研究进展

阐述了长周期光纤光栅(LPFG)化学传感器的结构与传感机理,介绍了LPFG化学传感器在化学溶液浓度测量方面的应用;讨论了光纤光栅化学传感器的最新研究热点——LPFC薄膜传感器;展望了LPFG化学传感器今后的发展方向。     

Non-solvent induced phase separation as a method for making high-performance chemiresistors based on conductive polymer nanocomposites

The fabrication of novel porous conductive composite vapor sensors characterized by different porosities and specific surface areas is described in this study. These samples were obtained by the dry-cast non-solvent induced phase separation (NIPS) method. Porous composite structures have been studied by the SEM, BET and water evaporation methods. Testing different concentrations of several organic vapors, the porous sensors showed improved sensitivities and response times as compared to their dense counterpart. Improved characteristics of the sensor response were correlated to better sorption and diffusion properties of sensing film due to increased porosity and specific surface area obtained by this method of film fabrication. A competition theory was proposed that describes the optimum porosity and thickness of sensing films in which the highest sensitivities were observed.     

Multi-wavelength optical fiber liquid refractometry based on intensity modulation

A novel approach of development of fiber optic sensor for measurement of refractive index of liquids is presented. This sensor uses two fibers, mirror as reflector and liquid as medium. The light is carried by the illuminating fiber up to modulation zone where the properties of incident light is modulated by modulator. The modulated light is carried by receiving fiber to the detector. The measurement principle is based on reflective intensity modulation. A novel sensing probe is designed with outer ring of fibers acting as illuminating fibers and center fiber acting as read fiber. Using this probe, effect of wavelength on refractive index is studied.     

石墨烯/聚二甲基硅氧烷三维非织造结构压阻柔性压力传感器

压阻式压力传感器是可穿戴器件中的关键元件。由于优异的弹性性能,本文以三维聚酯非织造布作为基材,还原氧化石墨烯(rGO)作为活性材料,聚二甲基硅氧烷(PDMS)作为柔性材料,组装三维(3D)压阻式压力传感器。该传感器具有良好的感应特性,包括短响应时间(120ms)和微弱的迟滞性(6.8%)。此外,该压力传感器可以用于检测人体的关节以及喉咙的运动情况。因此,该压阻传感器成本低、灵敏度高、耐久性优良,可以作为穿戴智能设备的理想的三维压阻式压力传感器。