Inkjet-printed monolayers as platforms for tethered polymers

Combining inkjet printing and atom-transfer radical polymerization (ATRP) provides a straightforward and versatile method for producing patterned polymer surfaces that may serve as platforms for a variety of applications. We report the use of drop-on-demand technology to print binary chemical gradients and simple patterns onto solid substrates and, by using surface-confined ATRP, amplify these patterns and gradients. Chemically graded monolayers prepared by inkjet printing dodecanethiol and backfilling with 11-mercaptoundecanol showed continuous changes in the water contact angle along the gradient. These samples also exhibited a distinct change in the intensity of methyl group and C-O stretching modes along the gradient. Graded or patterned polymer layers were produced by growing, with ATRP, tethered poly(methyl methacrylate) (PMMA) layers from gradient or patterned printed monolayers that contained a bromo-capped initiator. Atomic force microscopy and optical microscopy confirmed that the PMMA layers amplified the underlying printed initiator layer with remarkable fidelity.     

Carbon nanotube bags: catalytic formation, physical properties, two-dimensional alignment and geometric structuring of densely filled carbon tubes

The catalytic CVD synthesis, using propyne as carbon precursor and Fe(NO3)3 as catalyst precursor inside porous alumina, gives carbon nanotube (CNT) bags in a well-arranged two-dimensional order. The tubes have the morphology of bags or fibers, since they are completely filled with smaller helicoidal CNTs. This morphology has so far not been reported for CNTs. Owing to the dense filling of the outer mother CNTs with small helicoidal CNTs, the resulting CNT fibers appear to be stiff and show no sign of inflation, as sometimes observed with hollow CNTs. The fiber morphology was observed by raster electron microscopy (REM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The carbon material is graphitic as deduced from spectroscopic studies (X-ray diffraction, Raman and electron energy-loss spectroscopy (EELS)). From M?ssbauer studies, the presence of two different oxidation states (Fe0 and FeIII) of the catalyst is proven. Geometric structuring of the template by two different methods has been studied. Inkjet catalyst printing shows that the tubes can be arranged in defined areas by a simple and easily applied technique. Laser-structuring creates grooves of nanotube fibers embedded in the alumina host. This allows the formation of defined architectures in the microm range. Results on hydrogen absorption and field emission properties of the CNT fibers are reported.     

Fundamental study of crystallization,orientation, and electrical conductivity of electrospun PET/carbon nanotube nanofibers

The morphology, structure, and properties of polyethylene terephthalate (PET)/Carbon Nanotubes (CNT) conductive nanoweb were studied in this article. Nanocomposite nanofibers were obtained through electrospinning of PET solutions in trifluoroacetic acid (TFA)/dichloromethane (DCM) containing different concentrations and types of CNTs. Electrical conductivity measurements on nanofiber mats showed an electrical percolation threshold around 2 wt % multi‐wall carbon nanotubes (MWCNT). The morphological analysis results showed smoother nanofibers with less bead structures development when using a rotating drum collector especially at high concentrations of CNTs. From crystallographic measurements, a higher degree of crystallinity was observed with increasing CNT concentrations above electrical percolation. Spectroscopy results showed that both PET and CNT orientation increased with the level of alignment of the nanofibers when the nanotube concentration was below the electrical percolation threshold; while the orientation factor was reduced for aligned nanofibers with higher content in CNT. Considerable enhancement in mechanical properties, especially tensile modulus, was found in aligned nanofibers; at least six times higher than the modulus of random nanofibers at concentrations below percolation. The effect of alignment on the mechanical properties was less important at higher concentrations of CNTs, above the percolation threshold. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 2052–2064, 2010     

The influence of various deposition techniques on the photoelectrochemical properties of the titanium dioxide thin film

Thin sol–gel TiO₂ layers deposited on the conductive ITO glass by means of three various deposition techniques (dip-coating, inkjet printing and spray-coating) were used as photoanode in the three-compartment electrochemical cell. The thin TiO₂ films were treated at 450 °C and after calcination all samples possessed the crystallographic form of anatase. The relationship between surface structure and photo-induced conductivity of the nanostructured layers was investigated. It was found that the used deposition method significantly influenced the structural properties of prepared layers; mainly, the formation of defects and their quantity in the prepared films. The surface properties of the calcined layers were determined by XRD, Raman spectroscopy, SEM, AFM, UV–Vis analyses and by the optical microscopy. The photo-induced properties of nanoparticulate TiO₂/ITO photoanode were studied by electrochemical measurements combined with UV irradiation.     

铬酸及硝酸混合液处理以增强碳纳米管场发射

为了修饰碳纳米管(CNTs)的表面型态及改变碳纳米管的表面结构, 进一步增强碳纳米管的场发射特性, 使用铬酸及硝酸的混合溶液对碳纳米管进行后处理. 采用SEM、TEM、Raman 和EDS测试手段对样品的形貌、表面成份组成和微观结构特征进行了表征. 场发射(FE)的数据显示, 经过铬酸及硝酸的混合溶液处理20 min的碳纳米管场发射电流比未经任何处理的碳纳米管场发射电流明显增加一个数量级以上, 场发射电流增强的主要原因为样品上的碳纳米管的表面型态的改变, 造成碳纳米管场发射增强因子茁的增大. 与单独使用硝酸溶液后处理比较, 使用铬酸及硝酸的混合溶液对碳纳米管进行后处理可以得到较高的场发射电流及较低的起始电场. 铬酸及硝酸的混合溶液处理方法能经济且有效增强碳纳米管的场发射特性.     

An inkjet printing soft photomask and its application on organic polymer substrates

This article presents a simple, fast and low-cost method to fabricate a flexible UV light photomask. The designed micropatterns were directly printed onto transparent hybrid composite film of biaxially oriented polypropylene coated with silica oxide (BOPP-SiO _x ) by an inkjet printer. Compared to the conventional chrome-mask, it is of advantages such as suitable for non-planar substrates, scalable for large area production, and extreme low cost. Combined with the confined photo-catalytic oxidation (CPO) reaction, the printed flexible BOPP-SiO _x photomask was successfully used to pattern the shape of wettability of organic polymer surfaces, and then polyaniline patterns were deposited on the modified substrates with strong adhesion. With the above photomasks, the polyacrylic acid graft chains were duplicated on the poly (ethylene terephthalate) (PET) and BOPP substrates by photografting polymerization. We grafted polyacrylic acid (PAA) on a non-planar plastic substrate with this soft and thin plastic photomask. Scanning electron microscopy (SEM) and optical microscopy were used to characterize the surface morphology and thickness of ink layers of the printed photomask. Optical microscopy was used to characterize the deposition polyaniline micropatterns. It was found that the desired patterns were precisely printed on the modified polymer films and were applied in modifying organic polymer substrates. The printed photomask could be exploited in the fields such as prototype microfluidics, micro-sensors, optical structures and any other kind of microstructures which does not require high durability and dimensional stability.     

Patterned alignment of nematic liquid crystals generated by inkjet printing of gold nanoparticles and emissive carbon dots on both flexible polymer and rigid glass substrates

Patterned homeotropic alignment using nanoparticles (NPs) was achieved using inkjet printing. Two types of gold NPs, one smaller and one larger in core diameter (2 and 5 nm) capped with a monolayer of dodecanethiol, and emissive carbon dots with a core diameter of 2.5 nm featuring a mixed ligand shell of carboxylic acid groups and aliphatic hydrocarbon chains were tested on both rigid glass and flexible polycarbonate substrates. To define the director across the entire cell and not just in the NP-printed areas, alignment ‘underlayers’ were tested, and 30° obliquely evaporated SiO_x as alignment ‘underlayer’ generally provided the best results with the highest quality of the homeotropic alignment as well as the best contrast at the boundary between printed and non-printed (i.e. homeotropic and planar) domains of the fabricated cells. We also report that the chemical nature of the nematic liquid crystal (LC) used, the number of layers printed and the composition of the nano-ink need to be adjusted to obtain pattern alignment devices that positively benefit from both the properties of the LC and the nanomaterial printed.     

Enhancement of Field Emission Characteristics for Multi-Walled Carbon Nanotubes Treated with a Mixed Solution of Chromic Trioxide and Nitric Acid

A simple acid treatment method was applied to functionalize the surface and to modify the structures of multi-walled carbon nanotubes (CNTs) grown on silicon substrates using a mixed solution of chromic trioxide (CrO₃) and nitric acid (HNO₃). Scanning electron microscopy (SEM), transmission electron microscopy (TEM), Raman spectroscopy, and energy dispersive spectrometer (EDS) were employed to investigate the mechanism causing the modified field emission (FE) properties of the CNT films. After 20 min of CrO₃+HNO₃ treatment, the emitted currents were enhanced by more than one order of magnitude compared with those of the untreated CNTs. This large increase in emitted current can be attributed to the favorable surface morphologies, open-ended structures, and highly curved CNT surfaces in the CNT films. These factors altogether caused an increase in the field enhancement factors of CNTs. We also demonstrated that using a mixed solution of CrO₃+HNO₃ post-treatment exhibited a higher emission current and a lower turn-on electric field than in the CNTs treated with HNO₃. The method provides a simple, economical, and effective way to enhance the CNT field emission properties.     

Nanoinks in inkjet metallization — Evolution of simple additive-type metal patterning

Recent advances in the development of stable dispersions of nanophase metal particles have allowed the direct fabrication of metal patterns (e.g., printed circuits, RFID tags, touch screens, etc.) by simple additive type inkjet processes. Such processes replace the more costly and less environmentally friendly subtractive lithographic type photoprocesses involving selective etching of photoresists and metal layers and more complex additive type process using photocatalysts for patterned metal deposition by electroless plating processes and inkjet patterning of metal catalyst or catalyst precursor for subsequent metallization by electroless plating. The recent development of electrohydrodynamic jet printing (e-jet printing), in which the ink drop is ejected under the influence of an electric field, has allowed a significant resolution increase vs. conventional inkjet printing with a piezoelectric head (printing resolution of ca. 100 nm for e-jet printing vs. ca. 20 μm for inkjet printing).     

Study on chemical-solution-deposited lanthanum zirconium oxide film based on the Taguchi method

A statistical route, Taguchi Design, applied to the analysis of experimental factors for coating lanthanum zirconium oxide films on metal substrates by inkjet printer is presented. The synthesis of lanthanum zirconium oxide precursor is derived from a chemical solution containing lanthanum acetate hydrate, zirconium propoxide, propionic acid, glacial acetic acid, and methanol anhydrous. Experimental factors analyzed by Taguchi Design show that the ratio of lanthanum acetate to propionic acid and the concentration of precursor used for inkjet printing are the dominant factors for the quality of films. With the deduced optimum conditions, lanthanum zirconium oxide films reveal good surface morphology and high out-of-plane alignment that is consistent with the Taguchi prediction.     

Nanotubes as polymer composite reinforcing additive materials – A comparative study

Nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNTs) and their non-doped conventional counterparts, multiwalled carbon nanotubes (MWCNTs) were compared as polymer reinforcing additives in polyvinyl chloride (PVC) matrix. The nanotubes were synthetized by catalytic chemical vapor deposition (CCVD) method. The purity of both nanotubes was measured by thermogravimetric analysis (TGA) and found to be >91%. Further analysis on the morphology and size of the carbon nanotubes (CNTs) were performed by transmission electron microscopy (TEM). The PVC powder was impregnated with CNTs in ethanol by using tip ultrasonicator. The dispersion media was evaporated, and the CNT/PVC powder was used to produce polymer fibers. The orientation of carbon nanotubes in the PVC matrix was characterized by scanning electron microscopy (SEM), and the presence of nanotubes were confirmed in case of all PVC samples. It can be observed on the SEM images that the nanotubes are fully covered with PVC. The tensile strength of the nanotube containing samples was tested and the N-BCNT/PVC composite was found to be better in this sense, thanks to the extraordinary structure of the nanotube. In case of the N-BCNT/PVC composite the measured young modulus was 39.7% higher, while the elongation at brake decreased by 33.6% compare to the MWCNT/PVC composite. These significant differences in the mechanical properties of the composites can be explained with the stronger interaction between N-BCNTs and PVC.     

Dispersion of Carbon Nanotubes with “Green” Detergents

Solubilization of carbon nanotubes (CNTs) is a fundamental technique for the use of CNTs and their conjugates as nanodevices and nanobiodevices. In this work, we demonstrate the preparation of CNT suspensions with “green” detergents made from coconuts and bamboo as fundamental research in CNT nanotechnology. Single-walled CNTs (SWNTs) with a few carboxylic acid groups (3–5%) and pristine multi-walled CNTs (MWNTs) were mixed in each detergent solution and sonicated with a bath-type sonicator. The prepared suspensions were characterized using absorbance spectroscopy, scanning electron microscopy, and Raman spectroscopy. Among the eight combinations of CNTs and detergents (two types of CNTs and four detergents, including sodium dodecyl sulfate (SDS) as the standard), SWNTs/MWNTs were well dispersed in all combinations except the combination of the MWNTs and the bamboo detergent. The stability of the suspensions prepared with coconut detergents was better than that prepared with SDS. Because the efficiency of the bamboo detergents against the MWNTs differed significantly from that against the SWNTs, the natural detergent might be useful for separating CNTs. Our results revealed that the use of the “green” detergents had the advantage of dispersing CNTs as well as SDS.     

Critical aspects related to processing of carbon nanotube/unsaturated thermoset polyester nanocomposites

Carbon nanotubes (CNTs) have outstanding mechanical, thermal and electrical properties. As a result, particular interest has been recently given in exploiting these properties by incorporating carbon nanotubes into some form of matrix. Although unsaturated polyesters with styrene have widespread use in the industrial applications, surprisingly there is no study in the literature about CNT/thermoset polyester nanocomposite systems. In the present paper, we underline some important issues and limitations during the processing of unsaturated polyester resins with different types of carbon nanotubes. In that manner, 3-roll mill and sonication techniques were comparatively evaluated to process nanocomposites made of CNTs with and without amine (NH₂) functional groups and polyesters. It was found that styrene evaporation from the polyester resin system was a critical issue for nanocomposite processing. Rheological behaviour of the suspensions containing CNTs and tensile strengths of their resulting nanocomposites were characterized. CNT/polyester suspensions exhibited a shear thinning behaviour, while polyester resin blends act as a Newtonian fluid. It was also found that nanotubes with amine functional groups have better tensile strength, as compared to those with untreated CNTs. Transmission electron microscopy (TEM) was also employed to reveal the degree of dispersion of CNTs in the matrix.     

Production of aqueous colloidal dispersions of carbon nanotubes

Stable homogeneous dispersions of carbon nanotubes (CNTs) have been prepared by using sodium dodecyl sulfate (SDS) as dispersing agent. To our knowledge, it is the first report to quantitatively characterize colloidal stability of the dispersions by UV-vis spectrophometric measurements. When the sediment time reaches 500 h, the supernatant CNT concentration drops as much as 50% for the bare CNT suspension, compared to 15% with the addition of SDS. Furthermore, after 150 h, no precipitation is found for CNT/SDS dispersions, exhibiting an extreme stability. Zeta potential, auger electron microscopy, and FTIR analysis are employed to investigate the adsorption mechanism in detail. It has been concluded that the surfactant containing a single straight-chain hydrophobic segment and a terminal hydrophilic segment can modify the CNTs-suspending medium interface and prevent aggregation over long periods. The morphology of the CNT dispersions is observed with optical microscopy. An intermediate domain of homogeneously dispersed nanotubes exhibits an optimum at 0.5 wt% CNTs and 2.0 wt% SDS.     

A general route to prepare one- and three-dimensional carbon nanotube/metal nanoparticle composite nanostructures

Adsorption of polyethyleneimine (PEI)-metal ion complexes onto the surfaces of carbon nanotubes (CNTs) and subsequent reduction of the metal ion leads to the fabrication of one-dimensional CNT/metal nanoparticle (CNT/M NP) heterogeneous nanostructures. Alternating adsorption of PEI-metal ion complexes and CNTs on substrates results in the formation of multilayered CNT films. After exposing the films to NaBH4, three-dimensional CNT composite films embedded with metal nanoparticles (NPs) are obtained. UV-visible spectroscopy, scanning electron microscopy, and X-ray photoelectron spectroscopy are used to characterize the film assembly. The resulting (CNT/M NP)n films inherit the properties from both the metal NPs and CNTs that exhibit unique performance in surface-enhanced Raman scattering (SERS) and electrocatalytic activities to the reduction of O2; as a result, they are more attractive compared to (CNT/polyelectrolyte)n and (NP/polyelectrolyte)n films because of their multifunctionality.     

热解碳包覆的碳纳米管复合二氧化锰薄膜超级电容器

通过化学气相沉积(CVD)的方法,在碳纳米管(CNT)薄膜及其连接处沉积热解碳(PC)来限制CNTs之间的滑移。通过扫描电镜(SEM)观察发现,热解碳(PC)的沉积使得CNT表面更加平整,且表面的孔洞更加均匀。通过应力应变及亲疏水性测试发现,CNT/PC复合薄膜的拉伸强度增加了200%,水与薄膜的静态接触角由123°减小到78°。其后通过电化学沉积的方法,制备得到CNT/PC/MnO2薄膜电极材料,通过电化学测试得知,在1 mA/cm^2的电流下单电极的比电容为326 mF/cm^2,可以稳定循环10000圈,电容的保持率稳定在100%左右。     

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.     

Influence of Surface Properties on SEM Observation for Carbon Nanotubes with Pretreatment Using Room Temperature Ionic Liquids

In this study, we observed hydrophobic or hydrophilic carbon nanotubes (CNTs) by scanning electron microscopy (SEM); the samples were pretreated with room temperature ionic liquids (RTILs) to impart electrical conductivity to their surfaces. When the amount of RTIL on the sample surface and the affinity between the RTIL and sample surface were tuned, suitable electroconductive thin layers were formed on the sample surfaces. The presence of these layers allowed high-quality SEM images to be observed at the nano level. Suitable pretreatments for CNT were achieved using dilute RTIL/ethanol solutions. By optimizing these conditions, we acquired SEM images that were similar in quality to those of samples subjected to the conventional pretreatment of metal sputtering. The highest resolution of the SEM images was less than 30 nm.     

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.     

Inkjet printed Prussian blue films for hydrogen peroxide detection

An inkjet printing method is described to fabricate hydrogen peroxide (H(2)O(2)) sensors. Insoluble Prussian blue (PB) nanoparticles were dispersed in aqueous solvent, and were printed on screen printed carbon electrodes with a piezoelectric inkjet printer for H(2)O(2) detection. The electrochemical behavior of the printed sensors was studied by using cyclic voltammetry and chronoamperometry. The printed sensors showed great electrocatalytic activity toward H(2)O(2) and can be used for amperometric detection of H(2)O(2). The calibration curves for H(2)O(2) determination showed a linear range from 0.02 to 0.7 mM with a sensitivity of 164.82 μA M(-1) cm(-2) for the printed PB film. The results showed the feasibility of applying inkjet printing technology on surface modification; the results also provide an alternative way for manufacturing electrochemical sensors.