Self-assembly Of Carbon Nanotubes Research Articles

Highly efficient solar-driven water evaporation through a cotton fabric evaporator with wettability gradient

Harvesting light energy and converting it to heat as terminal energy by black photothermal sheets as evaporator is a novel strategy to attain fresh water. Although immense progress has been achieved in terms of the improvement of the evaporation rate and energy efficiency, it is still challenging to limit excessive water from entering the evaporator to eliminate the energy loss. Herein, a novel cotton fabric evaporator with a superhydrophobic-hydrophobic-hydrophilic-superhydrophilic wettability gradient (CFE-WG) was constructed by the layer-by-layer self-assembly of carbon nanotubes (CNTs), followed by separate modification with polyvinyl alcohol (PVA) and polydimethylsiloxane (PDMS). The wettability gradient in the thickness direction of CFE-WG permitted the slow transfer of water from the superhydrophilic side to the hydrophilic area and ultimately trapped the water at the hydrophilic/hydrophobic (water/air) evaporation interface, which avoiding the entry of excessive saline water inside the evaporator and maximally limiting thermal leakage. Under 1 sun irradiation, this CFE-WG exhibited a high vapor generation rate up to 1.54 kgm-2h-1, corresponding to an energy conversion efficiency of 93.7%. Notably, it could be used for desalination and wastewater treatment to collect fresh water that meets drinking requirements set by the WHO. This study provides a facile strategy to prepare a scalable evaporator for portable solar water purification, industrial solar-powered water treatment, and other advanced solar thermal applications.

Effect of surfactant concentration on the evaporation-driven deposition of carbon nanotubes: from coffee-ring effect to strain sensing.

Carbon nanotubes (CNTs) as electrically conductive materials are of great importance in the fabrication of flexible electronic devices and wearable sensors. In this regard, the evaporation-driven self-assembly of CNTs has attracted increasing attention. CNT-based applications are mostly concerned with the alignment of CNTs and the density of CNT films. In the present work, we focus on the latter by trying to achieve an optimal evaporation-driven deposition with the densest CNT ring. Although surfactants are used for effective dispersion and colloidal stabilization of CNTs in the aqueous phase, their excessive usage induces Marangoni eddies in the evaporating sessile droplets, leading to poor ring depositions. Thus, there is an optimum surfactant concentration that contributes to CNTs deagglomeration and results in the densest ring-like deposition with relatively high thickness. We report that this optimum concentration for sodium dodecyl sulfate (SDS) as a surfactant can be approximately considered as much as the concentration of multi-walled carbon nanotubes (MWCNTs) as the colloidal nanoparticles. Optimal depositions show the lowest electrical resistances for each CNT concentration, making them suitable for electronic applications. We also propose the multiple depositions method in which a new droplet is printed after the complete evaporation of the previous droplet. This method can lead to denser rings with a higher conductivity using lower concentrations of CNTs. Lastly, we fabricate strain sensors based on the optimal evaporation-driven deposition of CNTs which show higher gauge factors than the commercial strain gauges, corroborating the applicability of our method.

Self-assembly of carbon nanotubes on a hollow carbon polyhedron to enhance the potassium storage cycling stability of metal organic framework-derived metallic selenide anodes

Potassium-ion batteries (PIBs) is increasingly studied because of their suitable redox potential and high natural abundance. However, potential anode materials with long-term cycling stability are still in high demand because of the large radius of K+. Herein, an MOF-derived hierarchical carbon structure and the self-assembly of CNTs on hollow carbon polyhedrons are used as carbon matrices to disperse and stabilize metal selenides(Co-Se@CNNCP). When the hybrid is utilized in PIBs, it displays a specific capacity of 410 mA h g−1 at 0.1 A g−1 after 80 cycles and 253 mA h g−1 at 0.5 A g−1 after 200 cycles with a capacity retention of 100%, while the metal selenides dispersed on hollow carbon polyhedrons without CNTs (Zn-Co-Se@NCP) lose 86% of their capacity after 200 cycles. The superior cycling stability of the hybrid is mainly attributed to the large amounts of CNTs suppressing the agglomeration of the metal selenide nanoparticles on the surface, and the hollow carbon polyhedrons cause a high structural integrity during the repreated K+ insertion and extraction process. This work offers a feasible route to design a hierarchical carbon matrix for use as the anode materials of PIBs with long-term cycling stability.

Fabrication of superhydrophobic photothermal conversion fabric via layer-by-layer assembly of carbon nanotubes

Photothermal conversion material that generates thermal energy from sunlight is expected to be a promising technology for harvesting and conversion of clean solar energy. However, its photothermal conversion will be affected due to the surface contamination by dirt in outdoor applications, which greatly reduces the solar energy absorption. Herein, a superhydrophobic photothermal conversion fabric was fabricated through layer-by-lay self-assembly of carbon nanotubes (CNTs) on the surface of fibers, and followed by post-treatment with polydimethylsiloxane (PDMS). The CNTs not only impart to the fabric high photothermal conversion capability, but also construct roughening structures on the fiber surface. Consequently, the as-prepared fabric could be rapidly heated to 89.8 °C under one sun (1 kW/m2) irradiation, and showed excellent superhydrophobicity with contact angle 165° ± 0.9° and rolling angle 0.6° ± 0.2°. Meanwhile, the fabric possessed excellent stability to organic solvent, acid/alkali solutions, and UV irradiation. Importantly, the superhydrophobic self-cleaning property prevents the photothermal coating from contamination to guarantee the durability of the photothermal conversion efficiency.

Self-assembly of CNTs on Ni foam for enhanced performance of NiCoO2@CNT@NF supercapacitor electrode

Supercapacitors possess an essential application in storing intermittent energy and powering electric vehicles or wearable electronics. It should be a promising approach by combining carbon nanomaterials with metal oxides to promote energy density and maintain high power density and durable stability. Herein, carbon nanotubes (CNTs) were firstly organized on the surface of nickel foam (NF) by a facile and mild (room temperature) metal-induced self-assembly process. Afterward, NiCoO2 nanosheets are bonded by CNTs films via hydrothermal method, and then the integrated NiCoO2@CNTs@NF electrodes were successfully fabricated. The kinds of self-supporting electrodes have some advantages of hierarchical three-dimensional (3D) network structure, strong binding force between NiCoO2 nanosheets and Ni foam substrate, excellent conductivity tunnel for ions and electrons transport, and abundant active sites for ions adsorption and fast faradic redox reaction. Accordingly, the NiCoO2@CNTs@NF integrated electrode present the superior capacitive properties and stabilities because of outstanding synergistic effect between CNTs as electric double-layer capacitance (EDLC) materials and NiCoO2 nanosheets as Faradic pseudocapacitance materials. Asymmetric supercapacitors (ASCs) were also fabricated based on NiCoO2@CNTs@NF electrodes and active carbon supported on Ni foam electrodes. The ASCs show prominent performances of a high special capacitance (151 F g−1 at 5 mA cm−2), an outstanding rate capability (83.8% when current densities changed from 5 to 50 mA cm−2), durable stability (above 90% after 5000 cycles), and a high energy density (56.0 Wh kg−1). Such three ASCs devices connected in series can light up four blue light-emitting diodes (LEDs) that operates at a minimum voltage of 2 V. The presented work provides an efficient approach to design an outstanding electrode by combining active materials with a metal substrate.

Monotonic strain sensing behavior of self-assembled carbon nanotubes/graphene silicone rubber composites under cyclic loading

Conductive polymer composites can detect strain and pressure when subjected to large deformations. However, the complex strain sensing behaviors of the composites, such as the non-monotonic resistance response during cyclic loading, limit their further application. In this paper, the strain sensing behaviors have been optimally regulated through the synergistic effect and self-assembly of carbon nanotubes (CNTs) and graphene (GR) in silicone rubber (VMQ) composites. We found that the self-assembled CNTs-GR/VMQ composites have an incredibly low percolation threshold of 0.92 wt%, which is 53% lower than that of the CNTs/VMQ composites. Additionally, the resistance response of CNTs/VMQ and CNTs-GR/VMQ composites showed a significant downward drift and shoulder peak phenomenon, whereas the self-assembled CNTs-GR/VMQ composites exhibited a monotonic and more stable resistance response. Based on the morphology results of transmission electron microscopy and theoretical analysis, the uniform distribution of nanoparticles and the bridging structure formed by CNTs and GR are considered as the main reasons for the lower percolation threshold and the better resistance response.

Synergistic effect of DNA interfacing on carbon nanotube field effect transistor devices

Successful integration of carbon nanotubes (CNTs) in electronic devices and sensors requires controlled deposition at well defined locations and appropriate electrical contacts to metal electrodes/leads. Controlled self-assembly of CNTs can be achieved by interfacing them with biological molecule like DNA using its self-recognition property. However, these biointerfaces can produce undesirable changes in their device characteristics. Herein, we report an extensive study of effect of DNA interfacing on device characteristics of carbon nanotube field effect transistors and explored its synergistic effects as self-assembling element in future nanodevices. Single walled carbon nanotubes (SWNTs) are interfaced with DNA (via both covalent and non-covalent methodology) and electronic transport properties of corresponding field effect transistor devices have been studied in order to have an insight into changes in the electrical properties of SWNTs after interfacing. It was concluded that covalently linked DNA is not appropriate for self-assembly of carbon nanotubes in future nanodevices as it ruins its electrical characteristics.

Investigating limiting factors for self-assembly of carbon nanotubes: A molecular dynamics simulation study

Multi-scale patterned assembly and integration is an important solution to break through the industrial application of carbon nanotubes (CNTs). The strategy based on self-assembly has yielded fruitful achievements in the practice of fabricating patterns such as two dimensional arrays. However, the mechanism of self-assembly of CNTs and the key factors that limit the fidelity of patterns have always been an unresolved issue. In this paper, all-atomic molecular models for studying the mechanism of hydrophilic/hydrophobic self-assembly are established and some key factors limiting the fidelity of SWNTs patterns are thoroughly investigated. The results show that chiral indices have little effect on the results of self-assembly. Secondly, edge effect determines the assembly sequence on hydrophilic surface and self-assembly will not occur when M-SWNTs are above the hydrophilic/hydrophobic interface. Thirdly, the assembly sequence of M-SWNTs in different layers of the solution is dominated by the competition of H2O molecules. At last, shielding effect is very important for the study of how to improve the density of SWNTs in the pattern. The explicitly results are not only helpful to understand many phenomena in self-assembly process at the atomic scale but also will provide meaningful guidance in fabrication of SWNTs patterns to prevent distortion.

Sessile droplets containing carbon nanotubes: a study of evaporation dynamics and CNT alignment for printed electronics.

Carbon nanotubes (CNTs) are 1-dimensional (1D) and flexible nanomaterials with high electric conductivity and a high aspect ratio. These features make CNTs highly suitable materials for the fabrication of flexible electronics. CNTs can also be made into dispersions which can be used as the feedstock material for droplet-based 3D printing technologies, e.g., inkjet printing and aerosol jet printing to fabricate printed electronics. These printing techniques involve several physical processes including deposition of ink droplets on flexible polymeric substrates such as polyimides, evaporation of the solvent and formation of thin films of CNTs, all of which have not been thoroughly investigated. Besides, alignment of the CNTs in the resultant thin films dictates their electrical performance. In this work, we examine the effect of substrate temperature and CNT concentration on the evaporation dynamics and also the alignment in the deposition patterns. Evaporation-driven self-assembly of CNTs and their preferential alignment are observed. Image analysis and Raman spectroscopy are utilised to evaluate the degree of alignment of the CNT network. It is found that the contact line dynamics depends greatly on the CNT concentration. Besides, the substrate temperature plays a significant role in determining the order of the CNTs in the drying deposition pattern. Our findings show the possibility of controlling the film morphology and the degree of alignment of CNTs for printed electronics in the printing process.

Self-assembly of cross-linked carbon nanotube films for improvement on mechanical properties and conductivity

A facile strategy for cross-linked carbon nanotube film (CL-CNF) was carried out via self-assembly of carbon nanotubes (CNTs), which was achieved based on esterification and acylation reactions of functional CNTs respectively. Comparing with uncross-linked carbon nanotube film, this strategy could benefit for enhancing mechanical properties of CNF through altering the inter-tube interaction from weaker Van der Waals force to stronger chemical bonding, but not lost its conductivity. The tensile strength and Young’s modulus of CL-CNF were remarkably enhanced, which were higher 263% and 190% than uncross-linked CNF. Meanwhile, conductivity of CNF after cross-linking increased to 210%. In this paper, the forming ester and acylation bonding in CNT network led to differences of their morphology that were observed on nanoscale. This method promoted CL-CNF as a promising material to be applied in water treatment and self-heating materials.

(Invited) 3D Multifunctional Carbon Nanotube Networks

In the field of nanomaterials research, carbon nanotubes (CNTs), proved to possess unique physicochemical properties, owing to their nanoscale dimensions, that have been applied to improve the performance of existing processes or even design novel technologies. Recently, there has been a growing interest in obtaining natural and synthetic three-dimensional (3D) architectures instead of two-dimensional ones to increase the active surface-to-volume ratio throughout the entire 3D structure, which proves to be advantageous in several applications. The 3D macroscopic structures can be obtained from the assembly of nanomaterials like graphene, carbon nanotubes, polymers and similar others, following chemical and physical routes and the resulting properties derive from the combination of those of the nano-constituents and those due to the complex architecture (like porosity, lightweight and others). In this paper, we show that is possible to promote a direct self-assembly of CNTs to obtain 3D networks following a chemical vapor deposition route. The self-supporting internal structure consist of interconnected CNTs and to lesser extent of carbon fibers that form a random skeleton with micrometer-size open pores. The porous nature of the network is directly responsible for its lightweight and the hydrophobic and lipophilic behavior, therefore the material is called CNT-sponge (figure 1). In addition, the macroscopic assembly shows high structural stability and good electrical conductivity, and mechanical response. The experimental results obtained in our laboratory, demonstrate that this 3D new material can be successfully applied in different applications. In particular, they can be applied as active material to address some environmental challenges involving water treatment, energy production, and contaminant sensing. Other potential applications include their use as pressure-sensors, in photon-energy conversion devices and as guides in reconnection of segregated spinal explants. References Scarselli M., et al. Beilstein J. Nanotechnol. 6 (2015) 792–798; Camilli L., Scarselli, M. et al., Appl. Phys. Lett. 102, (2013) 183117; Camilli, L.; Scarselli, M. et al., Nanotechnology 25, (2014) 065701. Figure 1

Polyaniline/Carbon Nanotubes Composite Modified Anode via Graft Polymerization and Self-Assembling for Microbial Fuel Cells.

Microbial fuel cells (MFCs) are promising devices for sustainable energy production, wastewater treatment and biosensors. Anode materials directly interact with electricigens and accept electrons between cells, playing an important role in determining the performance of MFCs. In this study, a novel carbon nanotubes (CNTs) and polyaniline (PANI) nanocomposite film modified Indium-tin oxide (ITO) anode was fabricated through graft polymerization of PANI after the modification of γ-aminopropyltriethoxysilane (APTES) on ITO substrate, which was followed by layer-by-layer (LBL) self-assembling of CNTs and PANI alternatively on its surface. (CNTs/PANI)n/APTES/ITO electrode with low charge transfer resistance showed better electrochemical behavior compared to the bare ITO electrode. Twelve layers of CNTs/PANI decorated ITO electrode with an optimal nanoporous network exhibited superior biocatalytic properties with a maximal current density of 6.98 µA/cm2, which is 26-fold higher than that of conventional ITO electrode in Shewanella loihica PV-4 bioelectrochemical system. MFCs with (CNTs/PANI)12/APTES/ITO as the anode harvested a maximum output power density of 34.51 mW/m2, which is 7.5-fold higher than that of the unmodified ITO electrode. These results demonstrate that (CNTs/PANI)12/APTES/ITO electrode has superior electrochemical and electrocatalytic properties compared to the bare ITO electrode, while the cellular toxicity of CNTs has an effect on the performance of MFC with (CNTs/PANI)n/APTES/ITO electrode.

Self-Assembly of Carbon Nanotubes and Boron Nitride via Electrostatic Interaction for Epoxy Composites of High Thermal Conductivity and Electrical Resistivity

The self-assembled oxidized carbon nanotubes (oCNTs) with the silane functionalized hexagonal boron nitrides (oCNTs@fBN) via electrostatic interaction were used to improve the thermal conductivity while maintaining the electrical insulation properties of the epoxy composites. The oCNTs were separately immobilized on the edges of hexagonal boron nitride (hBN), which prevent oCNTs from continuously contacting with each other. The thermal conductivity and volume resistivity of oCNTs@fBN filler loaded epoxy composites were measured and compared with the epoxy composites with a filler of hBN, a mixed filler of oCNTs, and silane functionalized hBN (fBN). The thermal conductivity of the epoxy composites containing 20 wt% of oCNTs@fBN10 was 1.26 W·m-1·K-1, which is higher than 600% compared to that of neat epoxy and the volume resistivity of the epoxy composites was in an insulation region even at high content of oCNTs@fBN filler. The significant improvement in thermal conductivity was attributed to the formation of linkages between oCNTs and fBN and the good compatibility of oCNTs@fBN in the epoxy matrix.

Reinforced local heterogeneities in interfacial tension distribution in polymer blends by incorporating carbon nanotubes

The modification of interface using nanoparticles in emulsions and immiscible polymer blends introduces elaborate methods to develop functional materials. In this study, we perform dissipative particle dynamics simulations to evaluate the distribution of interfacial tension over a polymer-polymer interface in the presence of carbon nanotubes (CNTs). The localization and interfacial self-assembly of CNTs is discussed in connection with their aspect ratio (AR) and entropic contributions. The distribution of interfacial tension is demonstrated in terms of the distribution of pressure differences across the interface. The results show large variations in the local pressure differences in the vicinity of CNTs. These variations are more pronounced when low AR CNTs are incorporated into the blends. It is argued that the self-assembly of large AR CNTs at the interface severely restricts their domain of influence while random dispersions of low AR CNTs can effectively dominate the entire interface of the dispersed phase. These new findings can help explain the shape irregularities observed in the particle-covered droplets.

Self-assembly of carbon nanotubes in polymer melts: simulation of structural and electrical behaviour by hybrid particle-field molecular dynamics.

Self-assembly processes of carbon nanotubes (CNTs) dispersed in different polymer phases have been investigated using a hybrid particle-field molecular dynamics technique (MD-SCF). This efficient computational method allowed simulations of large-scale systems (up to ∼1 500 000 particles) of flexible rod-like particles in different matrices made of bead spring chains on the millisecond time scale. The equilibrium morphologies obtained for longer CNTs are in good agreement with those proposed by several experimental studies that hypothesized a two level "multiscale" organization of CNT assemblies. In addition, the electrical properties of the assembled structures have been calculated using a resistor network approach. The calculated behaviour of the conductivities for longer CNTs is consistent with the power laws obtained by numerous experiments. In particular, according to the interpretation established by the systematic studies of Bauhofer and Kovacs, systems close to "statistical percolation" show exponents t ∼ 2 for the power law dependence of the electrical conductivity on the CNT fraction, and systems in which the CNTs reach equilibrium aggregation show exponents t close to 1.7 ("kinetic percolation"). The confinement effects on the assembled structures and their corresponding conductivity behaviour in a non-homogeneous matrix, such as the phase separating block copolymer melt, have also been simulated using different starting configurations. The simulations reported herein contribute to a microscopic interpretation of the literature results, and the proposed modelling procedure may contribute meaningfully to the rational design of strategies aimed at optimizing nanomaterials for improved electrical properties.

Self-assembly of carbon nanotubes modified by hydropropylcellulose in aqueous solution

Hydropropylcellulose (HPC)-modified multi-wall carbon nanotubes (HPC-MWCNTs) were prepared by physical adsorption of HPC on the surface of MWCNTs. The modification decreased the contact angle of water on HPC-MWCNTs and increased their water dispersion ability. However, HPC-MWCNTs dispersed in water were not stable and precipitated on the bottom of the container after 2 days as cylindrical bundles with a diameter of 4–8 μm and a length of 25–35 μm. The cylindrical bundles were formed by self-assembly of HPC-MWCNTs by hydrophilic and hydrophobic interactions. [New Carbon Materials 2013, 29(1): 26–33]

Conductive polymer nanocomposites with hierarchical multi-scale structures via self-assembly of carbon-nanotubes on graphene on polymer-microspheres.

A novel and highly conductive 3-dimensional (3D) hierarchical multi-scale structure is formed by a new, simple, facile, and water-based method that enables practical production of conductive carbon nanofiller/polymer composites. More specifically, the π-π interaction between CNTs and graphene oxide (GO) is exploited to disperse conductive but non-polar CNTs with amphiphilic GO sheets to form a stable aqueous colloidal solution. Aqueous-dispersible latex-polystyrene microspheres are then added to enable the self-assembly processes of anchoring CNTs on GO and wrapping microspheres with GO-stabilized CNTs for the formation of an intriguing 3D hierarchical multi-scale structure. During this process, GO is reduced to conductive reduced-graphene oxide (RGO). The resultant RGO sheets act as "nano-walls" to prevent CNTs from randomly diffusing into the polymer bulk during thermal pressing of RGO-CNT/microspheres, which results in the formation of a 3D foam-like network of RGO-CNTs with high quality. The resultant composite with such a structure gives an ultra-low percolation threshold (0.03 vol% RGO-CNTs) and a reasonably high conductivity (153 S m(-1) at 4 vol% RGO-CNTs), which could satisfy various applications requiring both transparency and electrical conduction characteristics (e.g. transparent antistatic coatings, capacitive touch-screens, and transparent electronic devices).

Synthesis of carbon nanotubes on graphene quantum dot surface by catalyst free chemical vapor deposition

The growth of carbon nanotubes (CNTs) on graphene quantum dot surface has been explored using acetylene as the carbon source in a catalyst free chemical vapor deposition process. Dynamic studies were conducted to observe the CNT growth. The obtained nanotubes have a diameter distribution of 10–30nm and show medium graphitic quality. Transmission electron microscopy observations and dynamic studies indicate that the formation of CNTs follows a different mechanism from traditional growth models, in which a wire-to-tube process and self-assembling of CNTs are involved. On the basis of these observations, a tentative continuous growth model is proposed for the CNT growth.

Self-assembly of carbon nanotubes using magnetic positioning and alignment by drop drying

The electronic properties of Carbon Nanotubes (CNTs) have generated great interest in the field of Nanoelectronics. However there are certain bottle-necks, e.g., nanoscale manipulations involving the use of sophisticated instruments like Atomic Force Microscope (AFM) and Scanning Probe Microscope (SPM), pre-processing, post-processing and positioning of the CNTs at the targeted positions. These bottle-necks should be overcome in order to make use of the excellent electronic properties of the CNTs in functional nanoscale devices. Multi-Walled CNTs (MWCNTs) synthesized by Chemical Vapor Deposition are used in as-synthesized condition without any post-processing. The microelectrodes are fabricated using Electron Beam Lithography. Under the influence of an external magnetic field, the CNTs are self-assembled into the target electrodes and aligned using the drop drying phenomenon. The I–V characteristic of the device is studied.

Self-assembly of carbon nanotubes and antibodies on tumours for targeted amplified delivery

Single-walled carbon nanotubes (SWNTs) can deliver imaging agents or drugs to tumours and offer significant advantages over approaches based on antibodies or other nanomaterials. In particular, the nanotubes can carry a substantial amount of cargo (100 times more than a monoclonal antibody), but can still be rapidly eliminated from circulation by renal filtration, like a small molecule, due to their high aspect ratio. Here we show that SWNTs can target tumours in a two-step approach in which nanotubes modified with morpholino oligonucleotide sequences bind to cancer cells that have been pre-targeted with antibodies modified with oligonucleotide strands complementary to those on the nanotubes. The nanotubes can carry fluorophores or radioisotopes, and were shown to selectively bind to cancer cells in vitro and in tumour-bearing xenografted mice. The binding process is also found to lead to antigen capping and internalization of the antibody/nanotube complexes. The nanotube conjugates were labelled with both alpha-particle and gamma-ray emitting isotopes, at high specific activities. Conjugates labelled with alpha-particle generating 225Ac were found to clear rapidly, thus mitigating radioisotope toxicity, and were shown to be therapeutically effective in vivo.