Adhesion Of Nanotubes Research Articles

Improving the Adhesion of Multi-Walled Carbon Nanotubes to Titanium by Irradiating the Interface with He+ Ions: Atomic Force Microscopy and X-ray Photoelectron Spectroscopy Study.

A complex study of the adhesion of multi-walled carbon nanotubes to a titanium surface, depending on the modes of irradiation with He+ ions of the "MWCNT/Ti" system, was conducted using atomic force microscopy and X-ray photoelectron spectroscopy. A quantitative assessment of the adhesion force at the interface, performed using atomic force microscopy, demonstrated its significant increase as a result of treatment of the "MWCNT/Ti" system with a beam of helium ions. The nature of the chemical bonding between multi-walled carbon nanotubes and the surface of the titanium substrate, which causes this increase in the adhesion of nanotubes to titanium as a result of ion irradiation, was investigated by X-ray photoelectron spectroscopy. It was established that this bonding is the result of the formation of chemical C-O-Ti bonds between titanium and carbon atoms with the participation of oxygen atoms of oxygen-containing functional groups, which are localized on defects in the nanotube walls formed during ion irradiation. It is significant that there are no signs of direct bonding between titanium and carbon atoms.

Wettability and adhesion of nanotubes applied to the surface of titanium implants by anodic oxidation.

The aim of this study was to evaluate the wettability and adhesion of self-organized TiO2 nanotubes formed on the surface of 8 commercially pure titanium (CP-Ti) disks and 12 dental implants (n = 12) by anodization in a glycerol-H2O (50-50 v/v) electrolyte containing NH4F. Two disk specimens were not submitted to anodization (controls). The nanotubes thus obtained had average dimensions of 50 nm in diameter by 900 nm in length. The treated disk specimens were stored for 2, 14 and 35 days (n = 2), and the wettability of their surfaces was evaluated with a goniometer at the end of each storing period. The adhesion of nanotubes to titanium was evaluated by field emission scanning electron microscopy after subjecting the 12 implants to a simulation of clinical stress in two-part synthetic bone blocks. After installing the implants with the application of an insertion torque, the two halves of the block were separated, and the implants were removed. The nanotubes remained adhered to the substrate, with no apparent deformation. The contact angles after 14 days and 35 days were 16.47° and 17.97°, respectively, values significantly higher than that observed at 2 days, which was 9.24° (p < 0.05). It was concluded that the method of anodic oxidation tested promoted the formation of a surface suitable for clinical use, containing nanotubes with levels of wettability and adhesion to titanium compatible with those obtained by other methods found in the literature. The wettability, however, did not prove stable over the tested storage periods.

Interface Engineering and Direct Observation of Strengthening Behavior in Field‐Sintered Boron Nitride Nanotube–Magnesium Alloy Composite

Boron nitride nanotube (BNNT) is integrated in AZ31 magnesium alloy by field‐assisted powder metallurgy route. A mat of BNNT is sputter‐coated with pure Mg and then sandwiched between AZ31 alloy powders. This layered composite is consolidated by spark plasma sintering (SPS). A high processing pressure of 400 MPa aids in intimate alloy–nanotube adhesion due to localized deformation. Thermal diffusion between AZ31 and BNNT (at 400 °C sintering temperature) results in the formation of Mg3N2 and AlN nanophases at the interface. Due to ultrafast Joule heating during SPS, the reactions are kinetically controlled, and only trace amounts of products are formed without compromising the characteristics of the nanotubes. The interphases aid in reactive bonding between AZ31 and BNNT, which is essential for load‐bearing applications. In situ double cantilever loading of the composite inside the scanning electron microscope shows that the nanotubes bridge, resist, and delay crack propagation. These findings demonstrate the promise of thermally stable BNNTs as reinforcement for engineering lightweight Mg‐based structural composites.

Wettability and adhesion of nanotubes applied to the surface of titanium implants by anodic oxidation

Background: A good implant surface is crucial for osseointegration. Many types are described in literature like double acid etching, SLA and anodization.

Etch track-directed growth of carbon nanotubes on graphite

Crystallographically-oriented nanotubes are grown on highly-etched graphite surfaces. The nanotubes are found to align along preferred crystal directions of the graphite surface along the same directions as etch tracks. This indicates that the nanotubes adhere to the etch tracks, which are themselves oriented along the three zigzag directions of the graphite surface. This nanotube adhesion to etch tracks is supported by nanotubes that are observed to grow on top of and adjacent to the etch tracks. The adhesion of nanotubes adjacent to etch tracks suggests that strain modes at the vicinity of exposed graphene edges may allow for a lower free energy for nanotubes to be located at these locations. Direct evidence of this adhesion of nanotubes to the tops of graphene step edges is observed through their nanomanipulation. These results demonstrate that a greater net load is required to dislodge a nanotube from an edge than is needed to drag the same tube to that edge.

Functionalization of carbon nanotubes with (3‐glycidyloxypropyl)‐trimethoxysilane: Effect of wrapping on epoxy matrix nanocomposites

ABSTRACTIn this work, multiwalled carbon nanotubes (MWCNT), after previous oxidation, are functionalized with excess (3‐glycidyloxypropyl)trimethoxysilane (GLYMO) and used as reinforcement in epoxy matrix nanocomposites. Infrared, Raman, and energy‐dispersive X‐ray spectroscopies confirm the silanization of the MWCNT, while transmission electron microscopy images show that oxidized nanotubes presented less entanglement than pristine and silanized MWCNT. Thickening of the nanotubes is also observed after silanization, suggesting that the MWCNT are wrapped by siloxane chains. Field‐emission scanning electron microscopy reveals that oxidized nanotubes are better dispersed in the matrix, providing nanocomposites with better mechanical properties than those reinforced with pristine and silanized MWCNT. On the other hand, the glass transition temperature of the nanocomposite with 0.05 wt % MWCNT‐GLYMO increased by 14 °C compared to the neat epoxy resin, suggesting a strong matrix–nanotube adhesion. The functionalization of nanotubes using an excess amount of silane can thus favor the formation of an organosiloxane coating on the MWCNT, preventing its dispersion and contributing to poor mechanical properties of epoxy nanocomposites. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44245.

Engineering Preferential Adsorption of Single-Walled Carbon Nanotubes on Functionalized ST-cut Surfaces of Quartz

Horizontal alignment during synthesis of single-walled carbon nanotubes has been found experimentally along certain directions of well-defined quartz surfaces. The reasons for such alignment are here examined using first-principles computational analysis, as a function of structure and chemistry of the specific exposed facet, presence and location of OH and H functional groups, and degree of hydration of the surface. It is found that selective functionalization of low-coordinated surface sites may cause exposure of low-coordinated Si atoms that bond strongly to nanotube walls. On the other hand, saturation of low-coordinated oxygen also favors carbon nanotube adhesion to the substrate. As found previously on bare silica surfaces, a chirality preference is confirmed on functionalized surfaces toward zigzag over armchair nanotubes. Magnetization effects on the surface originated by the presence of adsorbed functional groups are found to enhance adsorption of arm-chair nanotubes compared to that on clean surfaces. On the basis of the findings, it is suggested that surfaces may be engineered to favor horizontal adsorption of specific chiralities along preferential directions.

Bio-Inspired Method to Improve the Carbon Nanotube Adhesion Strength Onto Substrates

Bio-Inspired Method to Improve the Carbon Nanotube Adhesion Strength Onto Substrates

Laser-Assisted Simultaneous Transfer and Patterning of Vertically Aligned Carbon Nanotube Arrays on Polymer Substrates for Flexible Devices

We demonstrate a laser-assisted dry transfer technique for assembling patterns of vertically aligned carbon nanotube arrays on a flexible polymeric substrate. A laser beam is applied to the interface of a nanotube array and a polycarbonate sheet in contact with one another. The absorbed laser heat promotes nanotube adhesion to the polymer in the irradiated regions and enables selective pattern transfer. A combination of the thermal transfer mechanism with rapid direct writing capability of focused laser beam irradiation allows us to achieve simultaneous material transfer and direct micropatterning in a single processing step. Furthermore, we demonstrate that malleability of the nanotube arrays transferred onto a flexible substrate enables post-transfer tailoring of electric conductance by collapsing the aligned nanotubes in different directions. This work suggests that the laser-assisted transfer technique provides an efficient route to using vertically aligned nanotubes as conductive elements in flexible device applications.

Optimized process for the inclusion of carbon nanotubes in elastomers with improved thermal and mechanical properties

AbstractThe effects of addition of reinforcing carbon nanotubes (CNTs) into hydrogenated nitrile–butadiene rubber (HNBR) matrix on the mechanical, dynamic viscoelastic, and permeability properties were studied in this investigation. Different techniques of incorporating nanotubes in HNBR were investigated in this research. The techniques considered were more suitable for industrial preparation of rubber composites. The nanotubes were modified with different surfactants and dispersion agents to improve the compatibility and adhesion of nanotubes on the HNBR matrix. The effects of the surface modification of the nanotubes on various properties were examined in detail. The amount of CNTs was varied from 2.5 to 10 phr in different formulations prepared to identify the optimum CNT levels. A detailed analysis was made to investigate the morphological structure and mechanical behavior at room temperature. The viscoelastic behavior of the nanotube filler elastomer was studied by dynamic mechanical thermal analysis (DMTA). Morphological analysis indicated a very good dispersion of the CNTs for a low nanotube loading of 3.5 phr. A significant improvement in the mechanical properties was observed with the addition of nanotubes. DMTA studies revealed an increase in the storage modulus and a reduction in the glass‐transition temperature after the incorporation of the nanotubes. Further, the HNBR/CNT nanocomposites were subjected to permeability studies. The studies showed a significant reduction in the permeability of nitrogen gas. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011

All‐Carbon Nanotube‐Based Flexible Field‐Emission Devices: From Cathode to Anode

AbstractThe fabrication of a flexible field‐emission device (FED) using single‐walled carbon nanotube (SWNT) network films as the conducting electrodes (anode and cathode) and thin multi‐walled CNT/TEOS hybrid films as the emitters is reported. P‐type doping with gold ions and passivation with tetraethylorthosilicate (TEOS) made the SWNT network film highly conductive and environmentally stable, and hence a good alternative to conventional indium tin oxide electrodes. CNT/TEOS hybrid emitters showed high current density, low turn‐on field, and long‐term emission stability, compared with CNT emitters; these characteristics can be attributed to the TEOS sol, acting both as a protective layer surrounding the nanotube tip, and as an adhesive layer enhancing the nanotube adhesion to the substrate. All‐CNT‐based flexible FEDs fabricated by this approach showed high flexibility in field emission characteristics and extremely bright electron emission patterns.

An efficient approach to control the morphology and the adhesion properties of anodized TiO 2 nanotube arrays for improved photoconversion efficiency

We investigate an efficient approach to control the surface morphology and the geometrical parameter of TiO 2 nanotubes, while improving its adhesion to underlying titanium substrate, which is the key to successful fabrication of electro-optical devices. By controlling the water content and using the previously used electrolyte, nanotube arrays with surface morphology, geometrical parameters and adhesion properties relevant to required applications can be achieved. On the basis of these results, a mechanism of chemical dissolution rate is discussed in detail, in particular, with respect to the variation of nanotube length, presence of surface aggregation on the top surface, and the adhesion of nanotubes to underlying titanium substrate. It is found that the enhanced chemical dissolution rate can help to dissolve off the surface aggregation parts and reduce the internal stress at the barrier layer–metal interface. As a result this adhesion characteristic between the nanotubes and the underlying metal layer can be significantly improved. The contrastive photoelectrochemical experiments suggested that the photoconversion efficiency greatly depends on the geometric roughness factor of nanotubes and its adhesion to underlying metal layer. It shows that the 3.0% water content in previously used electrolytes has a combinative advantage to meet the optimal condition of photoconversion efficiency.

Microstructural characterization of Al-MWCNT composites produced by mechanical milling and hot extrusion

Aluminum-based nanocomposites were produced using multiwalled carbon nanotubes (MWCNTs) dispersion by mechanical milling (MM) followed by sintering and hot extrusion. MWCNTs showed stability after MM and thermo-mechanical processes. Excellent adhesion of nanotubes to Al-matrix was observed. Formation of an amorphous interface between nanotubes and aluminum matrix in nanocomposites was observed by TEM. This amorphous layer is probably responsible of the excellent adhesion of MWCNTs to the aluminum matrix.

Structural interpretations of deformation and fracture behavior of polypropylene/multi-walled carbon nanotube composites

The deformation and crack resistance behavior of polypropylene (PP) multi-walled carbon nanotube (MWNT) composites have been studied and their interrelation to the structural attributes studied by transmission electron microscopy (TEM), atomic force microscopy (AFM), scanning electron microscopy (SEM), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC) and polarization light microscopy has been discussed. The composites were produced from industrial available MWNT by extrusion melt-mixing and injection-molding. In stress–strain measurements a strong increase in the yield stress and the Young’s modulus at low MWNT contents has been observed, which was attributed to an efficient load transfer between the carbon nanotubes and polypropylene matrix through a good polymer–nanotube adhesion as indicated by SEM. The extent of enhancement in mechanical properties above 1.5 wt.% of MWNT decreased due to an apparently increased tendency of clustering of carbon nanotubes. Several theoretical models have been taken into account to explain the mechanical properties and to demonstrate the applicability of such models to the system under investigation. The crack resistance behavior has been studied with the essential work of fracture (EWF) approach based on post-yield fracture mechanics (PYFM) concept. A maximum in the non-essential work of fracture was observed at 0.5 wt.% MWNT demonstrating enhanced toughness compared to pure PP, followed by a sharp decline as the MWNT content was increased to 1.5 wt.% reveals a ductile-to-semi-ductile transition. Studies on the kinetics of crack propagation aspects have revealed a qualitative picture of the nature of such a transition in the fracture modes.

Carbon nanotubes thin films fiber optic and acoustic VOCs sensors: Performances analysis

This work is focused on the performances analysis of silica optical fiber (SOF) and quartz crystal microbalance (QCM) volatile organic compounds (VOCs) sensors, coated by single-walled carbon nanotubes (SWCNTs) multilayers, towards toluene and xylene vapors, at room temperature. The Langmuir-Blodgett (LB) technique has been used for the deposition of carbon nanotubes directly onto the optical and acoustic sensors substrates. A time division multiplexing approach has been used in order to simultaneously test up to eight SOF and six QCM chemical sensors in the same test chamber. The results obtained demonstrate good sensitivity, fast response and high repeatability provided by the proposed sensors even at very low concentrations. Resolutions in the ppm and sub-ppm range have been found towards the tested VOCs, for both optical and acoustic transducers. The effects of the SWCNTs film thickness and even of a cadmium arachidate (CdA) buffer multilayer, exploited in the past to improve the adhesion of nanotubes onto the sensors substrates, on the performances of SOF and QCM transducers have been investigated. To the aim, several optical and acoustic sensors with a different number of SWCNTs LB layers, directly deposited onto optical fibers and quartz surfaces and buffered by a CdA linker material, have been fabricated and simultaneously exposed, at room temperature, to different concentration pulses of toluene and xylene. The results obtained demonstrate the possibility to use the data coming from carbon nanotubes SOF and QCM sensors to improve the VOC discrimination by means of the hybrid system based on these two complementary transducers by pattern recognition methods.

Measurement of the Adhesion Force between Carbon Nanotubes and a Silicon Dioxide Substrate

Carbon nanotube adhesion force measurements were performed on single-walled nanotubes grown over lithographically defined trenches. An applied vertical force from an atomic force microscope (AFM), in force distance mode, caused the tubes to slip across the 250-nm-wide silicon dioxide trench tops at an axial tension of 8 nN. The nanotubes slipped at an axial tension of 10 nN after being selectively coated with a silicon dioxide layer.

Selective Placement of Carbon Nanotubes on Metal-Oxide Surfaces

We describe a method to selectively position carbon nanotubes on Al2O3 and HfO2 surfaces. The method exploits the selective binding of alkylphosphonic acids to oxide surfaces with large isoelectric points (i.e. basic rather than acidic surfaces). We have patterned oxide surfaces with acids using both microcontact printing and conventional lithography. With proper choice of the functional end group (e.g., -CH3 or -NH2), nanotube adhesion to the surface can be either prevented or enhanced.