Nanotube Composite Thin Films Research Articles

Free-standing polymer/multiwalled carbon nanotubes composite thin films for high thermal conductivity and prominent EMI shielding

Lightweight composite materials with efficient thermal conductivity (TC) and high electromagnetic interference (EMI) shielding effectiveness (SE) are of paramount importance for a wide range of applications such as electronics, aerospace, and stealth technology. In this work, lightweight, flexible, and free-standing poly (vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP)/multiwalled carbon nanotube (MWCNT) composite thin films are fabricated by a single-step, solution casting method. Fabricated PVDF-HFP/MWCNT composite thin films are characterized by many physicochemical techniques such as Raman spectra, Fourier transform infrared spectra, X-ray diffractometer, and high-resolution transmission electron microscope. The resulting composite thin film exhibits a TC of 1.1 Wm−1K−1 at room temperature. Further analysis shows that the TC of the composite film is increased up to 1.8 Wm−1K−1 at 100 °C. As fabricated flexible and free-standing composite thin film (thickness ∼ 150 µm) exhibit an excellent EMI SE of ∼ 36 dB in the X-band region (8.2–12.4 GHz) at just 15 wt. % loading of MWCNT. The outstanding EMI shielding and high TC of PVDF-HFP/MWCNT composite films are attributed to the homogenous distribution and well-connected network of MWCNT within the polymer matrix, forming a conductive network throughout the composite film.

Electrical, mechanical, and optical changes in MWCNT-doped PMMA composite films

In this study, we report the preparation of poly (methyl methacrylate)/multi-walled carbon nanotube (MWCNT) composite thin films by simple and efficient solution mixing and ultrasonic method and the electrical, optical, and mechanical characterizations. Scattered light intensity ( I sc), tensile modulus ( E), and surface conductivity ( σ) of these composites have increased with the addition of MWCNT into the composite. The observed behavior in electrical, optical, and mechanical properties of the poly (methyl methacrylate)/MWCNT composites was interpreted by site and classical percolation theory. The optical mechanical and electrical percolation thresholds of poly (methyl methacrylate)/MWCNT composites were determined as φ op = 3 wt%, φ m = 0 wt%, and φσ = 5 wt%, respectively. The optical ( t op), mechanical ( t m), and electrical ( t σ) critical exponents were calculated as 2.23, 0.43, and 0.11, respectively. Both the tensile modulus and tensile strength of poly (methyl methacrylate)/MWCNT composites were increased with increasing MWCNT content until it reaches to 10 wt%. However, above φ = 10 wt%, the mechanical properties of the composites were decreased due to the aggregation of MWCNTs, while the toughness does not show a significant change until φ = 10 wt% MWCNT content, whereas it was decreased above this value.

Fabrication and characterization of cytochrome c-immobilized polyaniline/multi-walled carbon nanotube composite thin film layers for biosensor applications

ABSTRACT Cytochrome c (Cyt c)-immobilized thin films of electropolymerized polyaniline (PANI)/carboxylated multi-walled carbon nanotube (cMWCNT) composite on a glassy carbon (GC) electrode were prepared and applied for trace level detection of hydrogen peroxide. The chemical structure, elemental analysis and surface morphology of the prepared thin films were respectively examined by Fourier-transform infrared spectroscopy, energy dispersive X-ray spectroscopy and scanning electron microscopy. Their electrochemical properties were characterized using, electrochemical impedance spectroscopy, cyclic voltammetry, and amperometry techniques. The formal potential, average surface coverage, electron transfer rate constant, and charge transfer coefficient of the prepared electrodes were calculated to be −0.35 V, 3.1 × 10−9 mol cm−2, 3.01 s−1, and 0.37, respectively. The modified electrode was highly sensitive for hydrogen peroxide detection with a sensitivity of 97.6 nA μM−1 and a detection limit of 0.2 μmol L−1 in a linear response range of 2–600 μmol L−1. According to the obtained results, the proposed PANI/cMWCNT composite thin film could facilitate direct electron-transfer between the GC electrode surface and the redox center of Cyt c, indicating a promising application in next-generation biosensors.

Fully integrated carbon nanotube composite thin film strain sensors on flexible substrates for structural health monitoring

Multifunctional thin film materials have opened many opportunities for novel sensing strategies for structural health monitoring. While past work has established methods of optimizing multifunctional materials to exhibit sensing properties, comparatively less work has focused on their integration into fully functional sensing systems capable of being deployed in the field. This study focuses on the advancement of a scalable fabrication process for the integration of multifunctional thin films into a fully integrated sensing system. This is achieved through the development of an optimized fabrication process that can create a broad range of sensing systems using multifunctional materials. A layer-by-layer deposited multifunctional composite consisting of single walled carbon nanotubes (SWNT) in a polyvinyl alcohol and polysodium-4-styrene sulfonate matrix are incorporated with a lithography process to produce a fully integrated sensing system deposited on a flexible substrate. To illustrate the process, a strain sensing platform consisting of a patterned SWNT-composite thin film as a strain-sensitive element within an amplified Wheatstone bridge sensing circuit is presented. Strain sensing is selected because it presents many of the design and processing challenges that are core to patterning multifunctional thin film materials into sensing systems. Strain sensors fabricated on a flexible polyimide substrate are experimentally tested under cyclic loading using standard four-point bending coupons and a partial-scale steel frame assembly under lateral loading. The study reveals the material process is highly repeatable to produce fully integrated strain sensors with linearity and sensitivity exceeding 0.99 and respectively. The thin film strain sensors are robust and are capable of high strain measurements beyond

Engineering Crack Formation in Carbon Nanotube-Silver Nanoparticle Composite Films for Sensitive and Durable Piezoresistive Sensors.

We report highly sensitive and reliable strain sensors based on silver nanoparticle (AgNP) and carbon nanotube (CNT) composite thin films. The CNT/AgNP was prepared by a screen printing process using a mixture of a CNT paste and an AgNP ink. It is discovered that the sensitivity of such sensors are highly dependent on the crack formation in the composites. By altering the substrate use and the relative ratios of AgNPs and CNTs, the formation and propagation of cracks can be properly engineered, leading to piezoresistive strain sensors with enhanced sensitivity and robustness.Electronic supplementary materialThe online version of this article (doi:10.1186/s11671-016-1626-z) contains supplementary material, which is available to authorized users.

Fabrication of copper/carbon nanotube composite thin films by periodic pulse reverse electroplating using nanodiamond as a dispersing agent

A method for forming a carbon nanotube (CNT) reinforced copper (Cu) composite by an electrodeposition process has been developed. Nanoscale diamond particles were introduced as a dispersing agent to prevent aggregation of carbon nanotubes while performing electrodeposition, or what is commonly referred to as electroplating. The technique involves co-deposition of Cu and CNTs in an electroplating process that uses both direct current and a sequence of forward and reverse pulses. Reverse pulse times were varied in order to examine parameters for dispersion of carbon nanotubes in the resultant composite material. Electrical resistivity, surface morphology, and composite structure were investigated using a probe station, scanning electron microscopy, and x-ray diffraction, respectively. Experimental results show carbon nanotubes can be dispersed uniformly in a Cu/CNT composite due to the role played by the nanodiamond particles in CNT de-aggregation. Direct current electrodeposition yields high deposition rates while reverse pulse electrodeposition is a slower process although necessary for providing a higher percentage of CNTs integrated into the composite.

Transparent megahertz circuits from solution-processed composite thin films.

Solution-processed amorphous oxide semiconductors have attracted considerable interest in large-area transparent electronics. However, due to its relative low carrier mobility (∼10 cm(2) V(-1) s(-1)), the demonstrated circuit performance has been limited to 800 kHz or less. Herein, we report solution-processed high-speed thin-film transistors (TFTs) and integrated circuits with an operation frequency beyond the megahertz region on 4 inch glass. The TFTs can be fabricated from an amorphous indium gallium zinc oxide/single-walled carbon nanotube (a-IGZO/SWNT) composite thin film with high yield and high carrier mobility of >70 cm(2) V(-1) s(-1). On-chip microwave measurements demonstrate that these TFTs can deliver an unprecedented operation frequency in solution-processed semiconductors, including an extrinsic cut-off frequency (f(T) = 102 MHz) and a maximum oscillation frequency (f(max) = 122 MHz). Ring oscillators further demonstrated an oscillation frequency of 4.13 MHz, for the first time, realizing megahertz circuit operation from solution-processed semiconductors. Our studies represent an important step toward high-speed solution-processed thin film electronics.

Electrochemical Performance of Multi Walled Carbon Nanotube and Graphene Composite Films Using Electrophoretic Deposition Technique

This study aims to investigate multi-walled carbon nanotube and graphene composite thin films fabricated using cathodic electrophoretic deposition in aqueous solution. The deposition mechanism and films microstructure were investigated using the cyclic voltammetry (CV) and field emission scanning electron microscope. The depositions yield varied by the deposition time and deposition voltage. The composite films were studied for its application in the electrochemical capacitor. The electrochemical performance showed the capacitive behavior of the films in 6 M potassium hydroxide electrolyte. CV scans were verified from 0 to 1 V at different scan rates. The specific capacitance of 29 Fg-1 was achieved at the scan rate of 1 mVs-1.

Electrochemical co-deposition of sol–gel/carbon nanotube composite thin films for antireflection and non-linear optics

This work reports a method for electrodepositing sol–gel/CNT composite films. The deposition is highly selective to conductive surfaces, and the films exhibit non-linear optical properties and excellent antireflection performance.

Preparation and tribological properties of novel carbon nanotube self-assembled composite films

Carbon nanotube (CNT) composite thin films were prepared on a single-crystal silicon substrate by a self-assembling process from a specially formulated solution. Rare earth solution (RES) surface modification and appropriate acid-treatment methods were used to functionalise carbon nanotubes (CNTs). Silane coupling regent (3-mercaptopropyl trimethoxysilane (MPTS)) was prepared first. The terminal thiol groups (–SH) in the film was oxidised to sulphonic acid groups (–SO3H) in situ to enhance the film with good chemisorption ability. Treated Caron nanotubes were deposited on the oxidised MPTS–SAM by means of chemisorption with the SO3H group. The surface energy, chemical composition, phase transformation and surface morphology of the films were analysed using contact angle measurements, X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM) and atomic force microscopy. As a result, a conclusion could be made that some lanthanum elements react with –SO3H groups on the surface of the substrate by a chemical bond, which will improve the bonding strength between the films and the CNTs. Since the CNT thin films were well adhered to the silicon substrate, it might find promising application in the surface-modification of single-crystal Si and SiC in microelectromechanical systems (MEMS).

Mn(OH)2/multi-walled carbon nanotube composite thin films prepared by spray coating for flexible supercapacitive devices

Mn(OH)2/multi-walled carbon nanotube (MWCNT) composite thin films were obtained by spray coating on flexible indium tin oxide/polyethylene terephthalate substrate. The precursors for thin film deposition were prepared by completely mixing MWCNTs and KMnO4 in deionized water. The morphological characteristics of the films were examined by field emission scanning electronic microscopy and transmission electron microscopy. Phase evolution of the thin films was characterized by X-ray diffraction and X-ray photoelectron spectroscopy. As a result of the deposition process, Mn(OH)2 did not only cover the surface of MWCNTs uniformly but also embed in MWCNTs. The capacitive properties of the thin films were investigated by electrochemical measurements and the capacitance increased as the weight ratio of KMnO4/MWCNTs increased up to 1.6. The highest specific capacitance obtained at a scan rate of 20mVs−1 was 297.5F/g for the composite thin film with the weight ratio of KMnO4/MWCNTs of 1.2.

Preparation of bilayer/three-layer PEO-carbon nanotube composite thin films and their toluene-sensing application

The bilayer poly (ethylene oxide)/multiple-walled carbon nanotubes (PEO/MWCNTs) and three-layer PEO/MWCNTs/PEO composite thin films were fabricated with the spraying process on the interdigitated transducers (IDTs) as gas sensors for toluene-sensing application. Compared with the bilayer thin film sensor, the sensor with three-layer thin films exhibited higher response values and better recovery property. The microstructures of sensing films were characterized by scanning electron microscopy (SEM) to indicate that the better sensing response of three-layer thin films might be ascribed to the sufficient adsorption of toluene molecules on the surfaces of upper and bottom PEO films. The selectivity of the three-layer film sensor was further investigated by comparing responses upon exposure to different interference vapors with the response to toluene exposure, and much higher response was observed in the case of toluene. Good repeatability of the three-layer film sensor was also observed.

Superior separation performance of ultrathin gelatin films

Ultrathin gelatin films were prepared by filtering gelatin on a porous nanofibrous scaffold and cross-linked by glutaraldehyde. The gelatin thin films were obtained by using a copper hydroxide nanostrand scaffold after removal of the scaffold. At relative high pressure, the rejection properties of these gelatin films became worse due to mechanical fouling. However, the gelatin/carbon nanotube composite thin films prepared on a single-walled carbon nanotube scaffold could sustain a pressure up to 18 bars with more than 90% rejection for 2–3 nm molecules. The carbon nanotube layer dramatically increased the mechanical properties of the gelatin layer. The pressure dynamically controlled the network structure of the gelatin layer. The corresponding separation performances were investigated in detail. The gelatin films could be as thin as 62 nm. These gelatin films can separate 865 Dalton Direct Yellow 50 molecules at a rate of magnitude one to two orders higher than that of commercially available membranes with similar rejections.

High performance amorphous ZnMgO/carbon nanotube composite thin-film transistors with a tunable threshold voltage

Here we report the fabrication and characterization of high mobility amorphous ZnMgO/single-walled carbon nanotube composite thin film transistors (TFTs) with a tunable threshold voltage. By controlling the ratio of MgO, ZnO and carbon nanotubes, high performance composite TFTs can be obtained with a field-effect mobility of up to 135 cm(2) V(-1) s(-1), a low threshold voltage of 1 V and a subthreshold swing as small as 200 mV per decade, making it a promising new solution-processed material for high performance functional circuits. A low voltage inverter is demonstrated with a functional frequency exceeding 5 kHz, which is only limited by parasitic capacitance rather than the intrinsic material speed. The overall device performance of the composite TFTs greatly surpasses not only that of the solution-processed TFTs, but also that of the conventional amorphous or polycrystalline silicon TFTs. It therefore has the potential to open up a new avenue to high-performance, solution-processed flexible electronics which could significantly impact the existing applications, and enable a whole new generation of flexible, wearable, or disposable electronics.

Rational Design of Amorphous Indium Zinc Oxide/Carbon Nanotube Hybrid Film for Unique Performance Transistors

Here we report unique performance transistors based on sol-gel processed indium zinc oxide/single-walled carbon nanotube (SWNT) composite thin films. In the composite, SWNTs provide fast tracks for carrier transport to significantly improve the apparent field effect mobility. Specifically, the composite thin film transistors with SWNT weight concentrations in the range of 0-2 wt % have been investigated with the field effect mobility reaching as high as 140 cm(2)/V·s at 1 wt % SWNTs while maintaining a high on/off ratio ∼10(7). Furthermore, the introduction SWNTs into the composite thin film render excellent mechanical flexibility for flexible electronics. The dynamic loading test presents evidently superior mechanical stability with only 17% variation at a bending radius as small as 700 μm, and the repeated bending test shows only 8% normalized resistance variation after 300 cycles of folding and unfolding, demonstrating enormous improvement over the basic amorphous indium zinc oxide thin film. The results provide an important advance toward high-performance flexible electronics applications.

Effectively enhanced sensitivity of a polyaniline–carbon nanotube composite thin film bolometric near-infrared sensor

The polyaniline–carbon nanotube composite thin film bolometric near-infrared sensor exhibited more than a two orders of magnitude sensitivity enhancement over both the polyaniline thin film and carbon nanotube network NIR sensor. We also investigated the mechanism of the effectively enhanced sensitivity of the composite material and demonstrated that it is a synergistic effect due to the higher heat generation of carbon nanotubes and higher temperature coefficient of resistance of polyaniline.

Electro‐optical properties of electropolymerized poly(3‐hexylthiophene)/carbon nanotube composite thin films

Abstract3‐hexylthiophene was electropolymerized on a carbon nanotube (CNT)‐laden fluorine‐doped tin oxide substrate. Scanning electron microscopy and Raman spectroscopy revealed that the polymer was infused throughout the thickness of the 150‐nm thick CNT mat, resulting in a conducting composite film with a dense CNT network. The electropolymerized poly(3‐hexylthiophene) (e‐P3HT)/CNT composites exhibited photoluminescence intensity quenching by as much as 92% compared to the neat e‐P3HT, which provided evidence of charge transfer from the polymer phase to the CNT phase. Through‐film impedance and J‐V measurements of the composites gave a conductivity (σ) of 1.2 × 10−10 S cm−1 and zero‐field mobility (μ0) of 8.5 × 10−4 cm2 V−1 s−1, both of which were higher than those of neat e‐P3HT films (σ = 9.9 × 10−12 S cm−1, μ0 = 3 × 10−5 cm2 V−1 s−1). In electropolymerized samples, the thiophene rings were oriented in the (010) direction (thiophene rings parallel to substrate), which resulted in a broader optical absorbance than for spin coated samples, however, the lack of long‐range conjugation caused a blueshift in the absorbance maximum from 523 nm for unannealed regioregular P3HT (rr‐P3HT) to 470 nm for e‐P3HT. Raman spectroscopy revealed that π‐π stacking in e‐P3HT was comparable to that in rr‐P3HT and significantly higher than in regiorandom P3HT (ran‐P3HT) as shown by the principal Raman peak shift from 1444 to 1446 cm−1 for e‐P3HT and rr‐P3HT to 1473 cm−1 for ran‐P3HT. This work demonstrates that these polymer/CNT composites may have interesting properties for electro‐optical applications. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1269–1275, 2011

Ethanol-Assisted Graphene Oxide-Based Thin Film Formation at Pentane–Water Interface

Graphene oxide (GO) can be viewed as an amphiphilic soft material, which form thin films at organic solvent-water interfaces. However, organic solvent evaporation provides little driving force, which results in slow GO transfer in aqueous phase, thus dawdling GO film formation processes for various potential applications. We present an ethanol-assisted self-assembly method for the quick formation of GO or GO-based composite thin films with tunable composition, transmittance, and surface resistivity at pentane-water interface. The thickness of pure GO and reduced GO (rGO) films ranging from ~1 nm to more than 10 nm can be controlled by the concentration of GO in bulk solution. The transmittance of rGO films can be tuned from 72% to 97% at 550 nm while the surface resistivity changes from 8.3 to 464.6 kΩ sq(-1). Ethanol is essential for achieving quick formation of GO thin films. When ethanol is injected into GO aqueous dispersion, it serves as a nonsolvent, compromising the stability of GO and providing driving force to allow GO sheets aggregate at the water-pentane interface. On the other hand, neither the evaporation of pentane nor the mixing between ethanol and water provides sufficient driving forces to allow noteworthy amount of GO sheets to migrate from the bulk aqueous phase to the interface. This method can also be extended to prepare GO-based composites thin films with tunable composition, such as GO/single walled carbon nanotube (SWCNT) composite thin films investigated in this work. Reduced GO/SWCNT composite films show much lower surface resistivity compared to pure rGO thin films. This ethanol-assisted self-assembly method opens opportunities to design and fabricate new functional GO-based hybrid materials for various potential applications.

Suspended carbon nanotube nanocomposite beams with a high mechanical strength vialayer-by-layer nano-self-assembly

The fabrication and characterization of single-walled carbon nanotube(SWCNT) composite thin film micropatterns and suspended beams prepared bylithography-compatible layer-by-layer (LbL) nano-self-assembly are demonstrated.Negatively charged SWCNTs are assembled with a positively chargedpolydiallyldimethylammonium chloride, and the composite thin film is patterned by oxygenplasma etching with a masking layer of photoresist, resulting in a feature size of2 µm. Furthermore, the SWCNT nanocomposite stripe pattern with a metal clamp on both endsis released by etching a sacrificial layer of silicon dioxide in the hydrofluoric acid vapor.I–V measurement reveals that the resistance of SWCNT nanocomposite film decreases by 23%upon release, presumably due to the effect of reorientation of CNTs caused by thedeflection of about 50 nm. A high Young’s modulus is found in a range of 500–800 GPabased on the characterization of a fixed–fixed beam using nanoindentation. This value ismuch higher than those of the other CNT–polymer composites reported due toorganization of structures by self-assembly and higher loading of CNTs. The stiffCNT–polymer composite thin film micropattern and suspended beam have potentialapplications to novel physical sensors, nanoelectromechanical switches, other M/NEMSdevices, etc.

Transparent and flexible electrodes and supercapacitors using polyaniline/single-walled carbon nanotube composite thin films

Large-scale transparent and flexible electronic devices have been pursued for potential applications such as those in touch sensors and display technologies. These applications require that the power source of these devices must also comply with transparent and flexible features. Here we present transparent and flexible supercapacitors assembled from polyaniline (PANI)/single-walled carbon nanotube (SWNT) composite thin film electrodes. The ultrathin, optically homogeneous and transparent, electrically conducting films of the PANI/SWNT composite show a large specific capacitance due to combined double-layer capacitance and pseudo-capacitance mechanisms. A supercapacitor assembled using electrodes with a SWNT density of 10.0 µg cm(-2) and 59 wt% PANI gives a specific capacitance of 55.0 F g(-1) at a current density of 2.6 A g(-1), showing its possibility for transparent and flexible energy storage.