Effects of binders and organic vehicles on the emission properties of carbon nanotube paste

The different inorganic binders and organic vehicles were used to synthesize carbon nanotube (CNT) paste for field emission display. The morphologies, thermal and emission properties of the CNT paste with different components were investigated. The uniformity, the adhesion, and emission properties of CNT paste was improved when an inorganic binder changed from a glass frit to spin on glass (SOG). The current density increases by 5 times in magnitude when the ethyl cellulose solution was used instead of to acryl solution. The fabricated CNT emitter using photosensitive CNT paste showed high brightness of 18,000 cd/m² at low operating voltage of 1200 V.     

Simple approach for the fabrication of carbon nanotube field emitter using conducting paste

A conducting layer using carbon nanotube (CNT) paste was prepared by mixing multi-walled CNT (MWNT), organic vehicles and spin on glass (SOG). The effect of SOG on the properties of the CNT paste was evaluated and compared to that of CNT paste with a glass frit. CNT powders were coated on the conducting CNT film either by sprinkling CNT powders onto the overall conducting layer area or by dropping a solution containing well dispersed CNTs. CNTs were strongly fixed by the formation of silica after heat treatment. The samples showed good field emission characteristics with turn-on electric fields of approximately 1.6 ∼ 2.2 V/μm. SOG was found to be an efficient inorganic binder for CNTs in the CNT paste.     

Different filler effect of carbon nanotube and graphene nanoplatelet in the poly(arylene ether nitrile) matrix

The different filler effects of identical nitrile‐functionalized carbon nanotubes (CNTs) and graphene nanoplatelets (GNs) in a poly(arylene ether nitrile) (PEEN) matrix were investigated. PEEN/CNT and PEEN/GN composites were prepared by a facile solution‐casting method and systematically investigated for their differences in morphological, thermal and rheological properties. In the PEEN matrix GNs contact one another in a plane‐to‐plane manner, while CNTs are separated. Compared with PEEN/CNT composites, PEEN/GN composites below 2 wt% filler content exhibited higher thermal stability. Rheological properties of the resulting composites indicated that PEEN/GN composites were more sensitive to strain and exhibited higher η*, G′ and G″ than PEEN/CNT composites. The rheological percolation for CNTs is over 2 wt%, higher than that for GNs (around 1 wt%). All these differences originate from the different dimensions and structures of CNTs and GNs: GNs with a flake‐like structure and larger surface area can have stronger physical and interfacial interactions with the polymer matrix. This work gives a comparative view of the different filler effects that functionalized CNTs and GNs can have in the polymer host. With identical processing technology, GNs can show a stronger filler effect than CNTs. © 2012 Society of Chemical Industry     

Enhanced field emission properties of a reduced graphene oxide/carbon nanotube hybrid film

A facile vacuum filtration method for the preparation of hybrid films to achieve superior field emission properties from carbon nanotubes (CNTs) using reduced graphene oxide (rGO) as a bi-functional filler has been proposed. In the hybrid films, CNTs serve as electron emitters, while rGO helps to control the density of the CNT-emitters and reduce electrical resistance of the films. Via controlling volumes of CNTs and rGO dispersions, electron field emission properties of the hybrid films can be easily tailored. Higher weight ratio of rGO:CNT results in better electrical properties and the best field emission property is achieved when a rGO:CNT weight ratio of 1:3 is employed. The hybrid film reveals a significant improvement in field emission properties, as compared with the CNT film without adding rGO. Decreases in sheet resistance, turn-on field, and threshold field are attributed to the formation of extended conjugated network between CNTs and rGO in association with the reduction of screening effect through the optimization of density of CNT-emitters. The concept that rGO can be employed to control the density of CNT emitters will be of special interest for field emission enhancement.     

Low temperature growth of carbon nanotubes using Ni nanopowder mixed with Ag-paste as catalyst

Growth of carbon nanotubes (CNTs) at low temperature is a critical issue in the development of CNTs for diversified applications. The screen printing method, which used silver paste mixed with CNTs and glass powder as the raw material, was usually adopted for fabricating cathode of field emission device. In this work, Ni nanopowder mixed with commercial Ag-paste was prepared and screen-printed on the glass substrate, and then subjected to sintering in air at 500 °C. Growth of CNTs was performed in a self-designed cold-walled chemical vapour deposition (CVD) chamber at 500 °C under a pressure between 1 and 10 Torr. Field emission property was tested and the turn-on field of 2.4 V/μm was obtained for the specimen containing 2.7 wt.% Ni nanopowder. CNT density can be controlled by adjusting the concentration of Ni nanopowder in silver paste. This method proposed a simple route for synthesizing CNTs at relatively low temperature in a conventional CVD system, which is capable of fabricating large area cathode with proper CNT density.     

Stable Field Emitters for a Miniature X-ray Tube Using Carbon Nanotube Drop Drying on a Flat Metal Tip

Stable carbon nanotube (CNT) field emitters for a vacuum-sealed miniature X-ray tube have been fabricated. The field emitters with a uniform CNT coating are prepared by a simple drop drying of a CNT mixture solution that is composed of chemically modified multi-walled CNTs, silver nanoparticles, and isopropyl alcohol on flat tungsten tips. A highly thermal- and electrical-conductive silver layer strongly attaches CNTs to the tungsten tips. Consequently, the field emitters exhibit good electron emission stability: continuous electron emission of around 100 μA at 2.3 V/μm has stably lasted over 40 h even at non-high vacuum ambient (~10⁻³ Pa).     

Surface functionalization of carbon nanotubes by biological adhesive polymers carbopol for developing high‐permittivity polymer composites

Surface functionalization of carbon nanotubes (CNTs) by biological adhesive polymers carbopol (CP) was developed by simply mixing CNT suspension and an aqueous solution of CP without any toxic solvents. CP can be easily coated onto CNTs through hydrogen bonds O?C? OH?NH₂? C?O and electrostatic interaction between ? COO? on CP and ? NH₃⁺ on CNTs. After modification, the surface of the CNT is endowed with a large number of carboxyl groups, which can effectively prevent the reaggregation of CNT by electrostatic repulsion between the ionized carboxyl groups. Hence, highly dispersed functionally modifying CNT by CP (CP‐CNT) filler in polydimethylsiloxane (PDMS) matrix can be obtained. More important, with the help of adhesive properties of CP, the interfacial compatibility between fillers and matrix can also be improved. Thus, the CP‐CNT/PDMS composites exhibited higher dielectric permittivity comparing with CNT/PDMS composites at the same filler content. We present a potential and green approach of surface functionalization of CNT for preparing high‐permittivity polymer composites. J. VINYL ADDIT. TECHNOL., 26:165–172, 2020. © 2019 Society of Plastics Engineers     

Impact of ultrasonication on carbon nanotube demixing and damage in polymer nanocomposites

While ultrasonication is universally employed for dispersion and distribution of carbon nanotubes (CNTs) in a solvent or polymer solution, the current work focuses on the underlying mechanisms of CNT demixing and CNT damage that can occur during processing. Here, multi-walled CNTs were dispersed in a polycaprolactone polymer matrix using an established solution processing technique. Electrical, rheological, and mechanical characterization results suggest that once nanocomposite property enhancements reach an optimal level, further sonication leads to a decrease in the corresponding properties due to a combination of CNT damage and demixing mechanisms. Evidence of CNT damage from transmission electron microscopy, poor CNT distribution from optical image analysis and shear-induced crystallization results, and reagglomeration observed from ultraviolet–visible results, taken together, suggest that mechanisms of demixing and damage of the CNTs coexist for excessive sonication times.     

Rheological behavior and curing deformation of paste containing 85 wt% Al2O3 ceramic during SLA-3D printing

The preparation of high solids loading Al₂O₃ paste is of great significance for improving the properties of ceramics formed by UV-curing. However, the solid contents of alumina slurry used by digital light processing (DLP) and traditional alumina paste for stereolithography (SLA) are both less than 80 wt%. With increase in solid content, the viscosity of paste increases sharply, and rheological property deteriorates. In this study, ceramic paste containing 85 wt% (62 vol%) Al₂O₃ was prepared for SLA-3D printing of ceramics, and more than 85 wt% solid content was achieved by dispersant and other additives. Effects of different dispersants on rheological and curing properties of Al₂O₃ ceramic paste were studied. At room temperature, the viscosity of 85 wt% Al₂O₃ ceramic paste was 51733 mPa s at shear rate of 30 s^?1. A novel method was proposed to control curing deformation of parts during printing. As-manufactured ceramic did not show any cracks by naked eye and exhibited excellent mechanical properties, with three-point bending strength of 540 MPa, fracture toughness of 4.19 MPa m^1/2, Vickers hardness of 16 GPa, surface roughness of 0.463 μm, and density of 3.86 g/cm³.     

Effect of CNT decoration with silver nanoparticles on electrical conductivity of CNT-polymer composites

A simple approach to decorate carbon nanotube (CNT) with silver nanoparticles (Ag-NPs) was developed to enhance the electrical conductivity of CNT. CNTs were functionalized using ball milling in the presence of ammonium bicarbonate, followed by reduction of silver ions in N, N-dimethylformamide, producing silver decorated CNTs (Ag@CNTs). The Ag@CNTs were employed as conducting filler in epoxy resin to fabricate electrically conducting polymer composites. The electrical, thermal and mechanical properties of the composites were measured and compared with those containing pristine and functionalized CNTs. It was found that when pH was about six, highly dispersed Ag-NPs can be decorated on functionalized CNTs. The electrical conductivity of composites containing 0.10 wt% of Ag@CNTs was more than four orders of magnitude higher than those containing same content of pristine and functionalized CNTs, confirming the advantage of the Ag@CNTs as effective conducting filler. The ameliorating effect of improved electrical conductivity was not at the expense of thermal or mechanical properties.     

Improvement of electron field emission from carbon nanotubes by Ar neutral beam treatment

To improve the field emission properties of screen printed carbon nanotube (CNT) films, an Ar neutral beam was used as one of the surface treatment techniques and the CNT field emission characteristics after the treatment were compared with those after Ar ion beam treatment. The Ar neutral beam treatment enhanced the field emission properties of the CNTs and by decreasing the turn-on field and by increasing emission sites. When the field emission properties were measured after the treatment for 10 s with an energy of 100 eV, the turn-on field decreased from 1.7 to 0.9 V/μm while that after the ion beam treatment increased from 1.7 to 2.8 V/μm showing damage of exposed CNTs due to the intensive bombardment by the positive ions in the beam. The neutral beam treatment appeared to expose more CNT field emitters from the CNT paste without cutting or severely damaging the already exposed long CNT emitters because there were no charged particles in the beam.     

Effects of surface modification on rheological and mechanical properties of CNT/epoxy composites

Despite superior properties of carbon nanotubes (CNTs), physical properties of the CNT/epoxy composites are not improved significantly because interfacial bonding between the CNTs and the polymer matrix is weak. CNTs were treated by an acidic solution to remove impurities and modified subsequently by amine treatment or plasma oxidation to improve interfacial bonding and dispersion of nanotubes in the epoxy matrix. The functional groups on the surface of treated CNTs were investigated by X-ray photoelectron spectroscopy. The surface modified CNTs were embedded in the epoxy resin by ultra-sonication and the cured nanotube containing composites were characterized by field emission scanning electron microscopy. Rheological properties of nanotube containing epoxy resin and mechanical properties of the modified CNT/epoxy composites were improved because the modification of CNTs improved dispersion and interaction between the CNT and the epoxy resin.     

Assessment of intertube interactions in different functionalized multiwalled carbon nanotubes incorporated in a phenoxy resin

In this work, about 1 wt% of different functionalized carbon nanotubes (CNTs), namely CNT? COOH (CNT with carboxylic groups), CNT? NH₂ (CNT with amine groups) and CNT? OH (CNT with hydroxyl groups), as well as nonfunctionalized CNTs were incorporated into a phenoxy resin via a melt mixing process. The extent of intertubes and polymer–tubes interactions and their influence on state of CNTs dispersion were assessed through determination of electrical, rheological, and morphological characteristics. CNT? NH₂ showed the lowest intertubes interactions followed by CNT? OH and CNT? COOH. Nanocomposite made from CNT? COOH showed the poorest state of CNTs dispersion and the biggest CNTs agglomerates and it remained nonconductive. The acid‐functionalized CNTs were not able to form strong polymer–tube interactions because of their high cohesive energy and therefore in the melt rheological investigations they exhibited the lowest storage modulus and complex viscosity as well as the highest loss factor among all the studied CNTs. A good balance between intertubes and polymer–tube interactions is necessary through proper selection of CNTs functional groups for achieving a good state of CNTs dispersion and consequently obtaining enhanced electrical and viscoelastic properties. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Effect of surface treatment for carbon nanotubes on morphological and rheological properties of poly(ethylene oxide) nanocomposites

Poly(ethylene oxide) nanocomposites filled with functionalized multi‐walled carbon nanotubes are prepared and characterized using rheological and morphological measurements. This study investigates how the surface treatment of carbon nanotubes (CNTs) affects the CNT dispersion state. It is found that the nanocomposites have a higher effective volume fraction than the real volume fraction of the CNTs. The dispersion state of the CNTs is identified by using field emission scanning electron spectroscope and transmission electron microscope. The rheological findings indicate that there exists a percolated network structure of the CNTs in the nanocomposites, which was confirmed by electrical conductivity measurements as well as morphological observation. POLYM. ENG. SCI., 46:1350–1357, 2006. © 2006 Society of Plastics Engineers     

Factors influencing rheological characteristics of silver thick film paste and its correlation to multilayer ceramic processing

The rheological properties of silver thick film paste are influenced by the particle size, morphology of silver particles and by the nature of the filler. Rheological properties in-turn influence the multilayer processing parameters and properties. Silver particles, synthesised with gum Arabic (Ag/GA) as the dispersant resulted in agglomerated particles with irregular morphology. Ag/GA-based thick film paste exhibited thixotropic characteristics. Silver powder synthesised with polyvinyl alcohol (Ag/PVA) as the dispersant resulted in well-dispersed, spherical, free-flowing powder with narrow particle size distribution and exhibited pseudoplastic behaviour. The rheological characteristics of Ag/GA-based thick film paste are not influenced by the filler addition. Influence of filler addition is distinctly noted in the rheological characteristics of Ag/PVA-based thick film paste. The homogeneous mixing of Ag/PVA particles with filler and reproducible rheological characteristics of the corresponding thick film paste resulted in excellent printability with good edge-definition and repeatable properties.     

Rheological and conductive percolation laws for syndiotactic polystyrene composites filled with carbon nanocapsules and carbon nanotubes

Semicrystalline syndiotactic polystyrene (sPS) composites with carbon nanocapsule (CNC) and carbon nanotube (CNT) fillers were prepared and good filler dispersion confirmed by electron microscopy. Their rheological and electrical properties were investigated to reveal the effect of filler aspect ratio. Amorphous atactic polystyrene (aPS) was used to prepare composites with a CNT filler to elucidate the effect of matrix tacticity. Percolation scaling laws are applied and the threshold concentration and exponent are determined. Above a threshold, the magnitudes of storage modulus (G′) and conductivity are related to the level of percolation network as well as the intrinsic properties of the matrix and filler. Master curves are obtained provided that an appropriate percolation function is selected. Different scaling laws are validated for the G′ and conductivity results.Composites with CNTs show a much lower threshold than those with CNCs. A lower threshold is derived from the G′ results compared to that obtained from the conductivity data regardless of the filler aspect ratio and matrix tacticity. Owing to the pronounced nucleating effects of CNT, crystalline sPS composites exhibit a four times larger conductivity threshold compared to their amorphous aPS counterparts, although their rheological thresholds are similar.     

Master batch approach for developing PVDF/EVA/CNT nanocomposites with co-continuous morphology and improved electrical conductivity

Conducting polymer composites constituted by co-continuous poly (vinylidene fluoride) (PVDF)/ ethylene- vinyl acetate copolymer (EVA) blends with multiwalled carbon nanotube (CNT) were prepared by melt mixing using different procedures. The effect of the master batch approach on the conductivity, morphology, mechanical, thermal and rheological properties of PVDF/EVA/CNT nanocomposites was compared with that based on one step mixing strategy. The selective extraction experiments revealed that CNT was preferentially localized in the EVA phase in all situations, even when PVDF@CNT master batch was employed. Nanocomposites prepared with EVA@CNT master batch displayed higher conductivity, whose value reached around 10⁻¹ S m⁻¹ with the addition of 0.56 vol% of CNT. The better electrical performance was attributed to the better distribution of the filler, as indicated by transmission electron microscopy and rheological behavior. The electrical and rheological behavior were also investigated as a function of the CNT content.     

Highly stable carbon nanotube field emitters on small metal tips against electrical arcing

Carbon nanotube (CNT) field emitters that exhibit extremely high stability against high-voltage arcing have been demonstrated. The CNT emitters were fabricated on a sharp copper tip substrate that produces a high electric field. A metal mixture composed of silver, copper, and indium micro- and nanoparticles was used as a binder to attach CNTs to the substrate. Due to the strong adhesion of the metal mixture, CNTs were not detached from the substrate even after many intense arcing events. Through electrical conditioning of the as-prepared CNT emitters, vertically standing CNTs with almost the same heights were formed on the substrate surface and most of loosely bound impurities were removed from the substrate. Consequently, no arcing was observed during the normal operation of the CNT emitters and the emission current remained constant even after intentionally inducing arcing at current densities up to 70 mA/cm².     

Field emission properties from aligned carbon nanotube films with tetrahedral amorphous carbon coatings

Tetrahedral amorphous carbon (ta-C) film was coated on aligned carbon nanotube (CNT) films via filtered cathodic vacuum arc (FCVA) technique. Field electron emission properties of the CNT films and the ta-C/CNT films were measured in an ultra high vacuum system. The I–V measurements show that, with a thin ta-C film coating, the threshold electric field (E_thr) of CNTs can be significantly decreased from 5.74 V/μm to 2.94 V/μm, while thick ta-C film coating increased the E_thr of CNTs to around 8.20 V/μm. In addition, the field emission current density of CNT films reached 14.9 mA/cm² at 6 V/μm, while for CNTs film coated with thin ta-C film only 3.1 V/μm of applied electric field is required to reach equal amount of current density. It is suggested that different field emission mechanisms should be responsible for the distinction in field emission features of CNT films with different thickness of ta-C coating.     

Investigation on the Plasma-Induced Emission Properties of Large Area Carbon Nanotube Array Cathodes with Different Morphologies

Large area well-aligned carbon nanotube (CNT) arrays with different morphologies were synthesized by using a chemical vapor deposition. The plasma-induced emission properties of CNT array cathodes with different morphologies were investigated. The ratio of CNT height to CNT-to-CNT distance has considerable effects on their plasma-induced emission properties. As the ratio increases, emission currents of CNT array cathodes decrease due to screening effects. Under the pulse electric field of about 6 V/μm, high-intensity electron beams of 170–180 A/cm² were emitted from the surface plasma. The production mechanism of the high-intensity electron beams emitted from the CNT arrays was plasma-induced emission. Moreover, the distribution of the electron beams was in situ characterized by the light emission from the surface plasma.