Thermal transfer,interfacial, and mechanical properties of carbon fiber/polycarbonate-CNT composites using infrared thermography

Electrical resistance (ER) and thermogram measurements were used to evaluate thermal transfer, interfacial and mechanical properties of carbon fiber reinforced thermoplastic polycarbonate composites. Carbon nanotubes (CNTs) were fairly uniformly dispersed in polycarbonates using a solvent dispersion method. The CNTs were then further dispersed with an additional time using a twin screw extruder. The effect of CNT on the mechanical properties of polycarbonate was evaluated using a thin film tensile test. For thermogram to evaluate the transferring temperature the composite was placed on a hotplate and copper wires were inserted in the composite at uniform thickness intervals. Due to the different inherent thermal conductivity of CNT, ER was measured to detect thermal changes in the carbon fiber/CNT-polycarbonate composites. The comparison of interlaminar shear strength (ILSS) was to investigate effects of CNT on mechanical and interfacial properties. The uniform distribution of CNTs affected all of these properties in carbon fiber-reinforced thermoplastic composite. Furthermore, heat transfer and heat release become more rapid with the addition of CNT than the without case.     

碳纳米管薄膜的制备及其在柔性电子器件中的应用

近年来,柔性电子器件的发展日新月异。以碳纳米管为代表的碳纳米材料,尤其是其组装成的宏观结构碳纳米管薄膜具有良好的柔性和优异的导电性,且具有化学稳定、热稳定、光学透明性等优点,在柔性电子领域展现了极大的应用潜力。本文简要综述了近年来碳纳米管薄膜在柔性电子器件领域的研究进展。首先详细介绍了碳纳米管薄膜的两类主要制备方法,分别为干法制备和湿法制备;继而介绍了碳纳米管薄膜在多种柔性电子器件的组装、性能与应用方面的最新研究进展;最后总结了碳纳米管薄膜基柔性电子领域的发展现状,并讨论了该领域所面临的挑战及其未来前景。     

Preparing of high-quality carbon film from polyimide films by gradient heat treatment process

A series of carbon-graphite films were prepared via the gradient heating based on polyimide films under nitrogen atmosphere. FTIR spectroscopy, X-ray diffraction, Raman spectrum were used to systemically investigate the evolutions of chemical structure, crystal structure, thermal stability, morphological microstructure and properties of the carbon-graphite films. The study shows that the segment fracture and thermal cross-linking reaction occur first during the low temperature pyrolysis process of PI films, and the thermal cross-linking reaction changes the structure of polyimide. Radicals start restructuring and the thermal condensation becomes sharp with the increase of heat treatment temperature, and the amorphous structure of film is transformed into the ordered graphite structure, at the same time the crystallinity and orientation of the films are improved. When it reaches a certain temperature, the crystal lattice is further improved, and the structure of film can be transformed into polycrystalline graphite structure. With the increase of the temperature, the carbon content of film is gradually increasing, and the surface resistivity is smaller and smaller. It is obvious that once the continuous conductive network of carbon formed, the conductivity of composite sheet films hardly changed.     

Analysis of thermal parameters and factors acting on thermal conduction of low‐k films

The thermal properties of a silicon oxide‐based low‐k film and a thermally oxidized silicon film were investigated using the 3‐omega and laser thermo‐reflectance (LTR) methods. Thermal conductivity and effusivity were successfully estimated by the 3‐omega and LTR methods, respectively. It was confirmed that the combination of thermal effusivity and conductivity can successfully provide the heat capacity and thermal diffusivity of the films. The thermal parameters thus obtained suggested that the lower thermal conductivity of the examined low‐k film comes mainly from the rather low level of thermal diffusivity. Based on an analysis of the X‐ray diffraction profiles of the films, it was found that the low thermal diffusivity of the low‐k film can be attributed to the discontinuity of the network structure of their clusters. The heat resistance at the interface between the film and Si substrate was also evaluated. We found that the low‐k film exhibited, interestingly, negative interfacial heat resistance, although interfacial heat resistance should have a positive value in general. In order to determine the origin of the negative interfacial heat resistance, the interface state of the films was analyzed in detail on the basis of X‐ray reflectivity (XRR) measurements. The XRR results showed clearly that a thin, high‐density layer was present at the interface of the low‐k films. This high‐density layer presumably promoted heat flow to the substrate, resulting in the apparent negative interfacial heat resistance. Copyright © 2008 John Wiley & Sons, Ltd.     

Microstructural and Spectroscopic Studies of Sol-Gel Derived Silica-Titania Waveguides

Silica-titania planar waveguides were prepared via the sol-gel method from acid-catalyzed solutions of firstly, ÿ-Glycidoxypropyltrimethoxysilane mixed with tetrapropylorthotitanate (labeled as GT), and secondly, ÿ-Glycidoxypropyltrimethoxysilane mixed with both tetrapropylorthotitanate and tetraethoxysilane (labeled as GTT). Atomic force microscopy, thermal gravimetric analysis, differential thermal analysis, UV-visible spectroscopy, Fourier transform infrared spectroscopy, and Raman spectroscopy were used to study the structural and optical properties of the waveguide films prepared from the two types of sols. The obtained results showed that in both cases, crack-free and highly transparent silica-titania films with a thickness of more than 0.5 m could be obtained by a single spin-coating process after a heat treatment at 500°C. The GT derived films showed more shrinkage and a higher refractive index after annealing as compared to the GTT derived films. When such films were deposited on a silica-on-silicon substrate to act as a surface planar waveguide, the light propagation loss was measured to be about 0.9 dB/cm and 1.3 dB/cm respectively. Raman spectroscopy results indicated that the GTT derived waveguide films with 0.5 molar titanium content contained amorphous carbon phase after being heated at above 500°C in air directly.     

Hierarchically controlled helical graphite films prepared from iodine-doped helical polyacetylene films using morphology-retaining carbonization

One-handed helical graphite films with a hierarchically controlled morphology were prepared from iodine-doped helical polyacetylene (H-PA) films using the recently developed morphology-retaining carbonization method. Results from scanning electron microscopy indicate that the hierarchical helical morphology of the H-PA film remains unchanged even after carbonization at 800 °C. The weight loss of the film due to carbonization was very small; only 10-29% of the weight of the film before doping was lost. Furthermore, the graphite film prepared by subsequent heating at 2600 °C retained the same morphology as that of the original H-PA film and that of the helical carbon film prepared at 800 °C. The screwed direction, twisted degree, and vertical or horizontal alignment of the helical graphite film were well controlled by changing the helical sense, helical pitch, and orientation state of the chiral nematic liquid crystal (N*-LC) used as an asymmetric LC reaction field. X-ray diffraction and Raman scattering measurements showed that graphitic crystallization proceeds in the carbon film during heat treatment at 2600 °C. Transmission electron microscopy measurements indicate that ultrasonication of the helical graphite film in ethanol for several hours gives rise to a single helical graphite fibril. The profound potentiality of the present graphite films is exemplified in their electrical properties. The horizontally aligned helical graphite film exhibits an enhancement in electrical conductivity and an evolution of electrical anisotropy in which conductivity parallel to the helical axis of the fibril bundle is higher than that perpendicular to the axis.     

Highly transparent and conductive thin films fabricated with nano-silver/double-walled carbon nanotube composites

This study develops a technique for enhancing the electrical conductivity and optical transmittance of transparent double-walled carbon nanotube (DWNT) film. Silver nanoparticles were modified with a NH(2)(CH(2))(2)SH self-assembled monolayer terminated by amino groups and subsequent surface condensation that reacted with functionalized DWNTs. Ag nanoparticles were grafted on the surface of the DWNTs. The low sheet resistance of the resulting thin conductive film on a polyethylene terephthalate (PET) substrate was due to the increased contact areas between DWNTs and work function by grafting Ag nanoparticles on the DWNT surfaces. Increasing the contact area between DWNTs and work function improved the conductivity of the DWNT-Ag thin films. The prepared DWNT-Ag thin films had a sheet resistance of 53.4 Ω/sq with 90.5% optical transmittance at a 550 nm wavelength. After treatment with HNO(3) and annealing at 150 °C for 30 min, a lower sheet resistance of 45.8 Ω/sq and a higher transmittance of 90.4% could be attained. The value of the DC conductivity to optical conductivity (σ(DC)/σ(OP)) ratio is 121.3.     

Thermoelectric properties of nanocomposite thin films prepared with poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) and graphene

Carbon nanotubes (CNTs), either single wall carbon nanotubes (SWNTs) or multiwall carbon nanotubes (MWNTs), can improve the thermoelectric properties of poly(3,4-ethylenedioxythiophene) poly(styrenesulfonate) (PEDOT?:?PSS), but it requires addition of 30-40 wt% CNTs. We report that the figure of merit (ZT) value of PEDOT?:?PSS thin film for thermoelectric property is increased about 10 times by incorporating 2 wt% of graphene. PEDOT?:?PSS thin films containing 1, 2, 3 wt% graphene are prepared by solution spin coating method. X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy analyses identified the strong π-π interactions which facilitated the dispersion between graphene and PEDOT?:?PSS. The uniformly distributed graphene increased the interfacial area by 2-10 times as compared with CNT based on the same weight. The power factor and ZT value of PEDOT?:?PSS thin film containing 2 wt% graphene was 11.09 μW mK(-2) and 2.1 × 10(-2), respectively. This enhancement arises from the facilitated carrier transfer between PEDOT?:?PSS and graphene as well as the high electron mobility of graphene (200,000 cm(2) V(-1) s(-1)). Furthermore the porous structure of the thin film decreases the thermal conductivity resulting in a high ZT value, which is higher by 20% than that for a PEDOT?:?PSS thin film containing 35 wt% SWNTs.     

薄膜表面等离子体光催化剂Ag@AgBr/CNT/Ni的制备和性能

用复合电沉积技术制备了Ag@AgBr/CNT/Ni表面等离子体薄膜催化剂,以扫描电镜（SEM）、X射线衍射（XRD）、拉曼光谱（Raman Spectra）、X射线光电子能谱（XPS）和紫外-可见漫反射光谱（UV-Vis DRS）对薄膜的表面形貌、晶体结构、化学组成和光谱特性进行了表征,在可见光照射下,用罗丹明B（RhB）作为模拟污染物对薄膜的光催化性质和稳定性进行测定,采用测定薄膜电化学阻抗谱（EIS）和向反应系统中加入活性物种捕获剂的方法对薄膜光催化机制进行探索。结果表明：最优工艺下制备的Ag@AgBr/CNT/Ni薄膜是由少量碳纳米管（CNT）和表面沉积纳米Ag粒子的AgBr晶体构成的复合薄膜。薄膜具有突出的表面等离子体共振效应、优异的光催化活性和良好的催化稳定性。光催化罗丹明B 20 min,Ag@AgBr/CNT/Ni薄膜的降解率是Ag@AgBr/Ni薄膜的1.32倍,是P25 TiO₂/ITO多孔薄膜的21.6倍。在保持光催化性能基本不变的前提下可循环使用5次。CNT的存在使薄膜电荷传导性能和光催化还原溶解氧的性能大幅增加,是所制薄膜相对于Ag@AgBr/Ni薄膜光催化性能提高的主要原因。提出了薄膜光催化罗丹明B的反应机理。     

薄膜表面等离子体光催化剂Ag@AgBr/CNT/Ni的制备和性能

用复合电沉积技术制备了Ag@AgBr/CNT/Ni表面等离子体薄膜催化剂,以扫描电镜(SEM)、X射线衍射(XRD)、拉曼光谱(Raman Spectra)、X射线光电子能谱(XPS)和紫外-可见漫反射光谱(UV-Vis DRS)对薄膜的表面形貌、晶体结构、化学组成和光谱特性进行了表征,在可见光照射下,用罗丹明B(RhB)作为模拟污染物对薄膜的光催化性质和稳定性进行测定,采用测定薄膜电化学阻抗谱(EIS)和向反应系统中加入活性物种捕获剂的方法对薄膜光催化机制进行探索。结果表明:最优工艺下制备的Ag@AgBr/CNT/Ni薄膜是由少量碳纳米管(CNT)和表面沉积纳米Ag粒子的AgBr晶体构成的复合薄膜。薄膜具有突出的表面等离子体共振效应、优异的光催化活性和良好的催化稳定性。光催化罗丹明B 20 min,Ag@AgBr/CNT/Ni薄膜的降解率是Ag@AgBr/Ni薄膜的1.32倍,是P25 TiO_2/ITO多孔薄膜的21.6倍。在保持光催化性能基本不变的前提下可循环使用5次。CNT的存在使薄膜电荷传导性能和光催化还原溶解氧的性能大幅增加,是所制薄膜相对于Ag@AgBr/Ni薄膜光催化性能提高的主要原因。提出了薄膜光催化罗丹明B的反应机理。     

Spectroelectrochemical Evaluation of a ZnO Optically Transparent Electrode Prepared by the Spin‐spray Technique

We present a novel zinc oxide (ZnO) optically transparent electrode (OTE) prepared by the spin‐spray technique for spectroelectrochemistry. The spin‐spray technique can deposit ZnO film at a low cost, high rate deposition, and at a low temperature (<100 °C) in a single step. This new technique provides good optical transparency and electrical conductivity for ZnO. The electrochemical and spectroelectrochemical properties of the ZnO electrode were investigated for varying thicknesses of ZnO using methylene blue as a redox indicator. A ZnO OTE chip that includes three electrodes on a glass chip was developed for thin‐layer spectroelectrochemistry. Moreover, the ZnO films were successfully applied in an electrochemical‐localized surface plasmon resonance (LSPR) method for methylene blue detection by using them as a transparent conducting substrate for loading gold nanoparticles.     

Low Temperature Sol-Gel Preparation of Nanocrystalline TiO2 Thin Films

TiO₂ nanocrystalline thin films with varying degree of porosity have been prepared using a low temperature method. TiO₂ films of the anatase form have been obtained by using a polyethylene glycol (PEG) modified sol-gel method. Densification and crystallization of the films was found to result from the thermal treatment of the dip coated films in boiling water. The films have been characterized by Raman, XRD, FTIR, AFM and optical methods. Highly transparent films with transmission in excess of 85% and porosity as high as 58% are formed predominantly of anatase crystallites of dimensions of the order of 5 nm. Initial results on lithium intercalation into these films resulting in an efficient optical modulation in the visible and near infrared regions demonstrate a good potential of these films for electrochromic applications.     

Bulk synthesis of linear carbon chains confined inside single-wall carbon nanotubes by vacuum discharge

Carbyne, an infinite carbon chain, has attracted much interest and induced significant controversy for many decades. Recently, the presence of linear carbon chains (LCCs), which were confined stably inside double-wall carbon nanotubes (DWCNTs) and multiwall carbon nanotubes (MWCNTs), has been reported. In this study, we present a novel method to produce LCCs in a film of carbon nanotubes (CNTs). Our transmission electron microscopy and Raman spectroscopy revealed the formation of a bulk amount of LCCs after electric discharge of CNT films, which were used as field emission cathodes. The LCCs were confined inside single-wall CNTs as well as DWCNTs. Furthermore, two or three LCCs in parallel with each other are encapsulated when the inner diameter of CNT is larger than approximately 1.1 nm.     

Effects of CNT‐film Pretreatment on the Characteristics of NiCo2O4/CNT Core‐shell Hybrids as Electrode Material for Electrochemistry Capacitor

NiCo₂O₄/CNT nanocomposite films were fabricated by in‐situ growing ultrafine NiCo₂O₄ nanoparticles on acid‐modified carbon nanotube (CNT) films. The effects of CNT‐film pretreatment were investigated thoroughly by various characterization outfits including Fourier Transform Infrared spectroscopy (FT‐IR), X‐ray photoelectron spectroscopy (XPS), Raman spectroscopy, RTS‐9 four‐point probes resistivity measurement system, X‐ray powder diffraction (XRD), scanning electron microscopy (SEM) and CHI660D electrochemical workstation. These results suggested that carbon nanotubes were uniformly wrapped by NiCo₂O₄ nanoparticles forming a hierarchical core‐shell structure. And the crystallinity, conductivity of the CNTs and detail structure (both morphology and size) of the NiCo₂O₄ nanoparticles varied with prolonged acid treatment time which resulted in increased functional groups and defects on CNT films and further affected the electrochemical properties. The composite film composed of the CNT film pretreated by mixed acid for 12 h exhibited excellent electrochemical properties: 828 F/g at 1 A/g and 656 F/g at 20 A/g, and maintained over 99 % of its capacitance after 3000 cycles of charge/discharge at 5 A/g. Acid treatment for either too long or too short is detrimental to the electrochemical properties of the composite films. Such work should be of fundamental importance for tailoring electrochemical properties by elaborate design of acid treatment on CNTs.     

An Electrically and Thermally Erasable Liquid Crystal Film Containing NIR Absorbent Carbon Nanotube

Carbon nanotubes (CNTs) coated by a poly(vinylpyrrolidone) (PVP) layer were doped in bistable cholesteric liquid crystal (ChLC) film to provide electric, thermal, or optical erasability controllable films. The CNT/PVP formed a compatible NIR-absorbing film that can generate heat to switch ChLC film from a planar texture to a focal conic texture. The appropriate content of CNT/PVP is provided to achieve a fast thermal response, satisfactory dispersion, and clear display brightness. The ChLC film containing CNT/PVP @ 0.8 (wt.%) saves 51% time at thermal erasing, compared to the ChLC mixture without NIR absorbent. The hybrid organic–inorganic bistable ChLC material reported here extends and offers new applications of ChLC writing tablets.     

Highly Catalytic Carbon Nanotube/Pt Nanohybrid‐Based Transparent Counter Electrode for Efficient Dye‐Sensitized Solar Cells

Low‐cost transparent counter electrodes (CEs) for efficient dye‐sensitized solar cells (DSSCs) are prepared by using nanohybrids of carbon nanotube (CNT)‐supported platinum nanoparticles as highly active catalysts. The nanohybrids, synthesized by an ionic‐liquid‐assisted sonochemical method, are directly deposited on either rigid glass or flexible plastic substrates by a facile electrospray method for operation as CEs. Their electrochemical performances are examined by cyclic voltammetry, current density–voltage characteristics, and electrochemical impedance spectroscopy (EIS) measurements. The CNT/Pt hybrid films exhibit high electrocatalytic activity for I^?/I₃^? with a weak dependence on film thickness. A transparent CNT/Pt hybrid CE film about 100 nm thick with a transparency of about 70 % (at 550 nm) can result in a high power conversion efficiency (η) of over 8.5 %, which is comparable to that of pyrolysis platinum‐based DSSCs, but lower cost. Furthermore, DSSC based on flexible CNT/Pt hybrid CE using indium‐doped tin oxide‐coated polyethylene terephthalate as the substrate also exhibits η=8.43 % with J_sc=16.85 mA cm^?2, V_oc=780 mV, and FF=0.64, and this shows great potential in developing highly efficient flexible DSSCs.     

Effect of graphitization on the wettability and electrical conductivity of CVD-carbon nanotubes and films

The use of carbon nanomaterials in various applications requires precise control of their surface and bulk properties. In this paper, we present a strategy for modifying the surface chemistry, wettability, and electrical conductivity of carbon tubes and films through annealing in a vacuum. Experiments were conducted with 60-300 nm nanotubes (nanopipes), produced by noncatalytic chemical vapor deposition (CVD) in a porous alumina template, and with thin films deposited by the same technique on a glassy carbon substrate having the same structure and chemistry of the CNTs. The surface of the as-produced CVD-carbon, treated with sodium hydroxide to remove the alumina template, is hydrophilic, and the bulk electrical conductivity is lower by a factor of 20 than that of fully graphitic multiwalled nanotubes (MWNT) or bulk graphite. The bulk electrical conductivity increases to the conductivity of graphite after annealing at 2000 degrees C in a high vacuum. The analysis of CNTs by transmission electron microscopy (TEM) and Raman spectroscopy shows the ordering of carbon accompanied by an exponential increase of the in-plane crystallite size, L(a), with increasing annealing temperature. Environmental scanning electron microscopy (ESEM) was used to study the interaction of CNT with water, and contact angle measurements performed using the sessile drop method on CVD-carbon films demonstrate that the contact angle increases nearly linearly with increasing annealing temperature.     

Supramolecular Assemblies of Nucleoside Functionalized Carbon Nanotubes: Synthesis,Film Preparation,and Properties

Nucleoside‐functionalized multi‐walled carbon nanotubes ( N‐MWCNTs ) were synthesized and characterized. A self‐organization process using hydrogen bonding interactions was then used for the fabrication of self‐assembled N‐MWCNTs films free of stabilizing agents, polymers, or surfactants. Membranes were produced by using a simple water‐dispersion‐based vacuum‐filtration method. Hydrogen‐bond recognition was confirmed by analysis with IR spectroscopy and TEM images. Restoration of the electronic conduction properties in the N‐MWCNTs membranes was performed by removing the organic portion by thermal treatment under an argon atmosphere to give d‐N‐MWCNTs . Electrical conductivity and thermal gravimetric analysis (TGA) measurements confirmed the efficiency of the annealing process. Finally, oxidative biodegradation of the films N‐MWCNTs and d‐N‐MWCNTs was performed by using horseradish peroxidase (HRP) and low concentrations of H₂O₂. Our results confirm that functional groups play an important role in the biodegradation of CNT by HRP: N‐MWCNTs films were completely biodegraded, whereas for d‐N‐MWCNTs films no degradation was observed, showing that the pristine CNT undergoes minimal enzyme‐catalyzed oxidation This novel methodology offers a straightforward supramolecular strategy for the construction of conductive and biodegradable carbon nanotube films.     

Construction of various nanostructures on carbon nanotube films

Construction of nanostructures on surfaces has appealed intensive attention due to its significant applications in diverse fields. Especially, engineering surface properties via surficial nanostructures is actually the creation of functional interface-based materials and slated to be the key aspect for the future of materials science. Although many efforts have been made, there are only a few reports about the construction of nanostructures on carbon nanotube film surfaces. The big challenge for constructing on carbon films is that these carbon assemblies are easy to be dispersed by immersion in a chemical solution. Here, in this paper, we have shown for the first time the fabrication of different kinds of nanostructures, i.e. nanoneedles, nanoparticles, nanospirals, on carbon nanotube films by using facile and cheap electrodeposition method and precise physical deposition method. We pretreat the films by an electrical method to strengthen the films to avoid dispersion during the electrodeposition process. These composite films are still very flexible after coating with nanostructures. Compared with those precise physical deposition methods, the facile electrodeposition method is more suitable for constructing nanostructures on carbon nanotube films, due to the low requirement for planeness of films. It is interesting to find that these nanostructures can endow superhydrophobicity or higher conductivity for these flexible composite films, which greatly broaden the potential applications for carbon nanotube films in the fields of battery, moisture self-cleaning, electrostatic energy harvesting, and enhancing condensation heat transfer for more efficiency of energy utilization, environmental, and thermal management.     

Fabrication of flexible conducting thin films of copper-MWCNT from multi-component aqueous suspension by electrodeposition

Flexible thin films of metal–carbon nanotube (CNT) with densely populated CNT morphology were fabricated by electrodeposition from an optimized copper bath. The substrate used for the present work is polyethylene film that was pre-deposited with electroless copper as a seed layer before CNT deposition. Optimum concentration of CNT was incorporated into copper bath and the electrodeposition was done at quiescent and agitation conditions. The bonding between the seed layer and the electrodeposited copper was good as revealed from adhesion test. Electrical as well as physical-mechanical property of the film was improved by CNT incorporation within the metal matrix. The topography and the texture of the metal–CNT deposit showed a well-refined structure as per scanning electron microscope (SEM), field emission scanning electron microscope (FE-SEM), and scanning probe microscope (SPM) analysis. The stability of the film was tested by cyclic voltammetric and stripping analysis under various applied conditions. Raman spectra and Fourier transfer infrared spectroscopic (FT-IR) analysis revealed the presence of CNT and the functionality of CNT within the copper matrix. Transmission electron microscope (TEM) analysis showed nucleation of copper on the surface of CNT walls.