Preparation of chemical vapor sensing materials from composites of esterified poly(vinyl alcohol) and carbon black

Poly(vinyl alcohol) was modified by esterification to prepare poly(vinyl alcohol) copolymers. The degree of esterification on poly(vinyl alcohol) was elucidated by FTIR, ¹H NMR, and elemental analysis. The obtained products were poly(vinyl benzoate)-co-poly(vinyl alcohol) (B-PVA) and poly(vinyl p-toluoate)-co-poly(vinyl alcohol) (P-PVA). The chemical vapor sensors were fabricated by the mixtures of polymer and carbon black in dimethyl sulfoxide and their subsequent preparation as thin films onto the interdigited electrodes by the application of the spin-coating technique. The chemical vapor sensing properties of the sensors were examined with various solvents, such as hexane, toluene, methanol, ethanol, isopropanol, tetrahydrofuran, ethyl acetate, acetonitrile, dimethyl sulfoxide, and water. The experimental results indicated that modifying the chemical structure of PVA results in the decreased polarity of the obtained products. The composites of modified PVA consequently responded well to low polarity solvents, such as THF or ethyl acetate.     

Properties and characterization of carbon‐nanotube‐based transparent conductive coating

Abstract— Transparent and electrically conductive coatings and films have a variety of fast‐growing applications ranging from window glass to flat‐panel displays. These mainly include semiconductive metal oxides such as indium tin oxide (ITO) and polymers such as poly(3,4‐ethylenedioxythiophene) doped and stabilized with poly(styrenesulfonate) (PEDOT/PSS). In this paper, we show alternatives to ITO and conducting polymers, using single‐wall carbon nanotubes (SWNT). These CNT‐based technologies offer conducting substrates having a broad range of conductivity, excellent transparency, neutral color tone, good adhesion, abrasion resistance, and flexibility. Additional benefits include ease of both processing and patterning. This paper reports on optoelectronic properties and structure characterization of these materials.     

Vapour sensing with conductive polymer nanocomposites (CPC): Polycarbonate-carbon nanotubes transducers with hierarchical structure processed by spray layer by layer

The development of conductive polymer nanocomposite (CPC) sensors for volatile organic compounds (VOC) detection has been carried out using a spray layer by layer (LbL) process. This technique was successfully used to hierarchically structure polycarbonate-multiwall carbon nanotubes (PC-CNT) solutions into a double percolated architecture as attested by atomic force microscopy (AFM) and optical microscopy (OM). PC-CNT vapour sensing behaviour was investigated as a function of CNT content, films thickness, vapour flow and vapours solubility parameter. The response ranking A_r(toluene) > A_r(methanol) > A_r(water) of PC-CNT was found to be coherent with κ₁₂ Flory–Huggins interaction parameters provided that signals are normalised by analyte molecules number. Signals shape was interpreted to the light of Langmuir–Henry–Clustering (LHC) model and found to be proportional to vapour content.     

Chemo-sensitivity of latex-based films containing segregated networks of carbon nanotubes

In contrast to conventional hydrophobic Conductive Polymer nanoComposites (CPCs) used to design vapor sensors, which are mostly soluble in organic solvents, monodispersed acrylate copolymer latexes present the double advantage of being more sensitive and selective towards polar vapors such as water. A hierarchically structured latex based CPC film was obtained by co-dispersion of an aqueous acrylic emulsion with multiwalled carbon nanotubes (CNTs), followed by spray layer by layer (sLbL) assembly. The analysis of CPC films morphology by AFM and TEM show that a segregated network of CNT as been achieved by partial coalescence of latex nanoparticles and homogeneously assembled in 3D. Transducer sensitivity was investigated as a function of CNT content, latex glass transition temperature (T_g), organic vapor nature and vapor concentration. The source of the high sensitivity and selectivity observed for these latex-based composites towards water vapor is assumed to mainly result from ionic interaction of SDS with water molecules offering interesting perspectives of development. The different diffusion regimes through the CPC transducer are visualized, modeled and interpreted with the Langmuir-Henry-Clustering (LHC) model, showing that only water is reaching a clustering mode at high vapor concentration. Finally it is believed that the unique hierarchical architecture of BA latex-CNT sensors is responsible for their quick, stable and reproducible responses to vapors.     

A new numerical approach for low velocity impact response of multiscale-reinforced nanocomposite plates

In this paper, the low velocity impact analysis of carbon nanotube (CNT)/carbon fiber (CF)-reinforced hybrid nanocomposite plates is presented using variational differential quadrature (VDQ) method due to its numerical essence and the framework of implementation. The hybrid nanocomposite plate deformation is formulated based on classical plate theory and the contact force between the plate and projectile is estimated using Hertzian contact law. Also, a new micromechanics approach is presented to calculate the effective mechanical properties of the CNT/CF polymer hybrid nanocomposites. Five important factors including, random orientation and random distribution of CNTs, CNT/polymer interphase region, waviness and transversely isotropic behavior of CNT are incorporated in the micromechanical analysis. The accuracy of the present approach is verified with the available open literature results showing a clear agreement. The effects of various factors such as volume fraction and non-straight shape of CNT, CNT/polymer interphase region, CF volume fraction, random and regular arrangement of CFs, plate geometrical parameters and impactor velocity on the low velocity impact behavior of the CNT/CF-reinforced hybrid nanocomposite plates are studied.

     

聚酰亚胺（PI）树脂在电容式RF MEMS开关制作中的应用

聚酰亚胺树脂(PI)因其良好的平面化特性、在氧气中易灰化、不完全固化易溶解于碱性显影液、在CHF3等离子气氛中有较强的抗蚀性等性质,在电容RF MEMS开关的制作过程中,应用它作为刻蚀保护层和牺牲层,不但可以使工艺过程得到简化,而且可以对开关的介质层尺寸、牺牲层厚度等图形参数起到很好的控制作用.     

White organic light-emitting diodes with improved performance using phosphorescent sensitizer and ultrathin fluorescent emitter

White organic light-emitting diodes (WOLEDs) have been fabricated by using a novel phosphor of bis(1,2-dipheny1-1H-benzoimidazole) iridium (acetylacetonate) [(pbi)₂Ir(acac)] as a sensitizer doped into a carbazole polymer of poly(N-vinylcarbazole) (PVK), and a fluorescent dye of 4-(dicyanomethylene)-2-t-butyl-6-(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran(DCJTB) as an ultrathin red light-emitting layer. By characterizing the UV–Vis absorption spectra, photoluminescence (PL) spectra of (pbi)₂Ir(acac) and DCJTB, and the electroluminescence (EL) properties of the WOLEDs, the effect of ultrathin fluorescent light-emitting layer on the injection and transport characteristics of charge carrier and EL performance of WOLEDs was investigated. The results demonstrated that the device has stable EL spectra and Commissions Internationale de 1’Eclairage (CIE) coordinates in a wide bias range. Both energy transfer and charge trapping play the role on the performance of WOLEDs, and the device luminance was enhanced significantly with a maximum luminance of 9260 cd/m², which is about 70% higher than the codoped device.     

Estimation of average contact number of carbon nanotubes (CNTs) in polymer nanocomposites to optimize the electrical conductivity

The present paper suggests an equation for the average contact number of carbon nanotubes (CNTs) in CNT-reinforced polymer nanocomposites (PCNT) by two developed equations for electrical conductivity. Several novel parameters in PCNT such as CNT size, CNT concentration, network fraction, interphase depth, tunneling effect, and CNT wettability by the polymer medium are considered to define the average contact number (m). “m” is calculated for some samples and the variation of “m” is explored over a range of parameters’ values. The results show that dense interphase, high fraction of networked CNTs, reedy and short CNTs, low CNT surface energy, high polymer surface energy, low tunneling distance, and small contact diameter increase the “m” improving the conductivity. Moreover, tunneling distance and CNT contact diameter have the greatest effects on the “m”. The optimized level for “m” is necessary to control the nanocomposite’s conductivity.

     

Graphitic carbon nanofiber-poly(acrylate) polymer brushes as gas sensors

Carbon nanofiber/interdigitated array circuits fabricated with as-prepared herringbone graphitic carbon nanofibers [GCNF], GCNFs surface-derivatized with 3,4′-oxydianiline functional groups [GCNF–ODA], and GCNF–poly(butyl acrylate) [GCNF–PBA] or GCNF–poly(acrylic acid) [GCNF–PAA] polymer brushes are evaluated as solid-state gas-sensing materials unsupported by a polymer matrix. Vapor detection is observed as an increase in circuit electrical resistance. Analyte maximum response values exhibit chemoselectivity among different types of GCNF sensors and range over five orders of magnitude in parallel with expected trends in vapor/GCNF van der Waals interaction.     

Platinum (II) Porphyrin-Containing Thermoresponsive Poly(N-isopropylacrylamide) Copolymer as Fluorescence Dual Oxygen and Temperature Sensor

A random copolymer, poly(NIPAAm-co-PtPorphyrin), consisting of N-isopropylacrylamide (NIPAAm) and platinum (II) porphyrin units, behaves as an optical dual sensor for oxygen and temperature. The dual sensor is designed by incorporating an oxygen-sensitive platinum (II) porphyrin (M1) into a temperature-sensitive polymer (PNIPAAm). The polymer exhibited low critical solution temperature (LCST) property at 31.5 °C. This LCST affected the polymer's aggregation status, which in turn affected the nanostructures, fluorescence intensities, and responses to dissolved oxygen. This enables the polymer to functionalize as a dual temperature and dissolved oxygen sensor. Oxygen response of the platinum (II) porphyrin probes in the polymer followed a two-site Stern-Volmer model, indicating the nonuniform distribution of the probes. The copolymer was used to preliminarily monitor the oxygen consumption of Escherichia coli (E. coli) bacteria. The results indicate a potential application of the polymer in biological fields.     

A selective conductive polymer-based sensor for volatile halogenated organic compounds (VHOC)

A novel poly(p-xylylene), PPX, derivative bearing alkoxyphenyl side groups was electrochemically synthesized in 87% yield. The polymer, poly(4′-hexyloxy-2,5-biphenyleneethylene) (PHBPE), presented a fraction (92%) soluble in common organic solvents. It showed to be thermally resistant up to 185 °C. UV–vis analysis revealed an E_gap of 3.5 eV. Gas sensors made from thin films of 10-camphorsulfonic acid-doped PHBPE deposited on interdigitated electrodes exhibited significant changes in electrical conductance upon exposure to five VHOCs: 1,2-dichloroethane, bromochloromethane, trichloromethane, dichloromethane and tetrachloromethane. The conductance decreased after exposure to tetrachloromethane and increased after exposure to all the other VHOCs. Three-dimensional plots of relative response versus time of half response versus time of half recovery showed good discrimination between the five VHOCs tested.     

Automated classification of building information modeling (BIM) case studies by BIM use based on natural language processing (NLP) and unsupervised learning

This paper comparatively analyzes a method to automatically classify case studies of building information modeling (BIM) in construction projects by BIM use. It generally takes a minimum of thirty minutes to hours of collection and review and an average of four information sources to identify a project that has used BIM in a manner that is of interest. To automate and expedite the analysis tasks, this study deployed natural language processing (NLP) and commonly used unsupervised learning for text classification, namely latent semantic analysis (LSA) and latent Dirichlet allocation (LDA). The results were validated against one of representative supervised learning methods for text classification—support vector machine (SVM). When LSA and LDA detected phrases in a BIM case study that had higher similarity values to the definition of each BIM use than the threshold values, the system determined that the project had deployed BIM in the detected approach. For the classification of BIM use, the BIM uses specified by Pennsylvania State University were utilized. The approach was validated using 240 BIM case studies (512,892 features). When BIM uses were employed in a project, the project was labeled as “1”; when they were not, the project was labeled as “0.” The performance was analyzed by changing parameters: namely, document segmentation, feature weighting, dimensionality reduction coefficient (k-value), the number of topics, and the number of iterations. LDA yielded the highest F1 score, 80.75% on average. LDA and LSA yielded high recall and low precision in most cases. Conversely, SVM yielded high precision and low recall in most cases and fluctuations in F1 scores.     

Uniform carbon‐nanotube emitter for field‐emission displays

Abstract— The synthesis of carbon‐nanotube (CNT) field emitters for FEDs by thermal chemical vapor deposition (CVD) and their structural and emission characterization are described. Multi‐walled nanotubes (MWNTs) were grown on patterned metal‐base electrodes by thermal CVD, and the grown CNTs formed a network structured layer covering the surfaces of the metal electrode uniformly, which realized uniform distribution of electron emission. A technique for growing narrow MWNTs was also developed in order to reduce the driving voltage. The diameter of MWNT depends on the growth temperature, and it has changed from 40 nm at the low temperature (675°C) to 10–15 nm at the high temperature (900–1000°C). Moreover, narrower MWNTs were grown by using the metal‐base electrode covered with a thin alumina layer and a metal catalyst layer. Double‐walled nanotubes (DWNTs) were also observed among narrow MWNTs. The emission from the narrow CNTs showed a low turn‐on electric field of 1.5 V/μm at the as‐grown layer.     

Efficiency enhancement in blue organic light emitting diodes with a composite hole transport layer based on poly(ethylenedioxythiophene):poly(styrenesulfonate) doped with TiO2 nanoparticles

Blue color organic/polymeric light emitting diodes are very important because they can be used for tri-color display applications, fluorescence imaging, and exciting yellow phosphor for generating white light for general illumination. But the efficiency of blue organic/polymeric light emitting diodes is considerably low due to their large band gap that requires higher energy for effective emission. In this paper we report the enhancement in polyfluorene blue organic light emitting diodes with a polymer nano-composite hole transport layer. Blue light emitting diode based on polyfluorene as an emissive layer and poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate)–titanium dioxide nanocomposite as the hole transport layer were fabricated and studied. Different concentrations of titanium dioxide nanoparticles were doped in poly(3,4 ethylenedioxythiophene):poly(styrenesulfonate) in the hole transport layer and the performance of the devices were studied. Significant enhancement in the blue peak at 430 nm of polyfluorene has been observed with increase in concentration of TiO₂ nanoparticles in the hole transport layer. The turn on voltage of the device has also been found to improve significantly with the incorporation of titanium dioxide nanoparticles in the hole transport layer. The optimized concentration of titanium dioxide in the hole transport layer for most efficient device has been found to 15 wt.%.     

A hybrid chemiresistive sensor system for the detection of organic vapors

A five node sensor array, consisting of three films of gold nanoparticles functionalized with p-terphenylthiol, dodecanethiol and mercapto-(triethylene glycol) methyl ether, and films of poly(3-hexylthiophene) and polypyrrole, was integrated into a portable, microprocessor-based system. The system was evaluated for the detection of chloroform, diisopropyl methylphosphonate (DIMP), ethanol, hexane, methanol, and toluene vapors. Direct comparison of the five sensor films with respect to sensitivity, response time and recovery time was made by measurement of the resistance changes upon simultaneous exposure to each analyte. In general, the sensor films responded, with greatest sensitivity, to organic analyte molecules with similar chemical functionality (e.g., polarity). For example, the dodecanethiol-functionalized gold nanoparticle film sensor excelled at detecting hexane, while the mercapto-(triethylene glycol) methyl ether-functionalized nanoparticle film exhibited superb detection of ethanol and chloroform. Although the poly(3-hexylthiophene) film was very sensitive to polar analytes, including DIMP, in many cases it suffered from relatively long recovery times. Following training of the sensor system, successful differentiation and detection of the analytes were realized using a relatively simple algorithm based on “minimization of the squares of differences” method. The ability of the system to optimally differentiate these analytes is considered within the context of principal component analysis, and the effects of long-term sensor drift are discussed.     

A novel technique for fabrication of micro- and nanofluidic device with embedded single carbon nanotube

This paper describes a novel technique for fabrication of micro- and nanofluidic device that consists of a carbon nanotube (CNT) and a polydimethylsiloxane (PDMS) microchannel. Single CNT was placed at desired locations using dielectrophoresis (DEP) and PDMS microchannel was constructed on the aligned CNT via photolithography and soft lithography techniques. This technique enables a CNT to be seamlessly embedded in a PDMS microchannel. Moreover, controlling the PDMS curing condition enables the construction of the device with or without a CNT (the device without CNT has a trace nanochannel in PDMS). Preliminary flow tests such as capillary effect and pressure-driven flow were performed with the fabricated devices. In the capillary effect tests, the flow stopped at the nanochannel in both devices. In the pressure-driven flow lower flow resistance was observed in the device with a CNT.     

Irreversible sensing of oxygen ingress

Absorption-based opto-chemical sensors for oxygen are presented that consist of leuco dyes (leuco indigo and leuco thioindigo) incorporated into two kinds of polymer matrices. An irreversible and visible color change (to red or blue) is caused by a chromogenic chemistry involving the oxidation of the (virtually colorless) leuco dyes by molecular oxygen. The moderately gas permeable copolymer poly(styrene-co-acrylonitrile) and a highly oxygen-permeable polyurethane hydrogel, respectively, are used in order to increase the effective dynamic range for visualizing and detecting oxygen. We describe the preparation and properties of four different types of such oxygen sensors that are obtained by dip-coating a gas impermeable foil made from poly(ethylene terephthalate) with a sensor layer composed of leuco dye and polymer.     

Designing of MIP-based QCM sensor for the determination of Cu(II) ions in solution

A novel quartz crystal microbalance (QCM) sensor with a high selectivity and sensitivity has been developed for the determination of Cu(II) ions, based on the modification of Cu(II) ion-imprinted polymer (Cu(II)-IIP) film onto a quartz crystal. The performance of the developed MIP-QCM sensor was evaluated and the results indicated that a sensitive MIP-QCM sensor could be fabricated. The obtained MIP-QCM sensor presents high-selectivity monitoring of Cu(II) ions, better reproducibility, shorter response time (6 min), wider linear range (0.001–50 μM) and lower detection limit (8 × 10⁻⁴ μM). The practical analysis of the MIP-QCM sensor confirms the feasibility of Cu(II) determination in wastewater.     

医用电子鼻气体传感器阵列优化方法

电子鼻气体传感器阵列存在冗余和相关,将对分类识别效果产生影响。提出并实现了一种新的医用电子鼻气体传感器阵列优化方法,利用改进遗传算法设定气体传感器的重要性系数,以去除传感器阵列的冗余和相关,提高系统的判别能力。新的方法分别用于五种乳癌特征气体和七种伤口病原菌检测,使正确识别率得到较大提高。     

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.