Brownian motion-induced water slip inside carbon nanotubes

Molecular dynamics simulations are performed to understand the characteristics of the one-dimensional Brownian motion of water columns inside carbon nanotubes (CNTs) at room temperature. It is found that the probability of 2–10-nm-long water columns sliding a distance larger than the energy barrier period inside 2–5-nm-diameter CNTs is greater than 50 %. Moreover, a conservative estimation gives that the thermal fluctuation-induced driving force exceeds the upper bound of the sliding energy barrier for a water column shorter than 117 nm. These findings imply that although water molecules form layered structures near the CNT inner walls, there is no critical interfacial shear stress to conquer, and water could slip inside CNTs under any given pressure drop due to the thermal activation at room temperature.     

Coarse-grained molecular dynamics simulation of water diffusion in the presence of carbon nanotubes

Computational modeling of the translational diffusion of water molecules in anisotropic environments entails vital relevance to understand correctly the information contained in the magnetic resonance images weighted in diffusion (DWI) and of the diffusion tensor images (DTI). In the present work we investigated the validity, strengths and weaknesses of a coarse-grained (CG) model based on the MARTINI force field to simulate water diffusion in a medium containing carbon nanotubes (CNTs) as models of anisotropic water diffusion behavior. We show that water diffusion outside the nanotubes follows Ficḱs law, while water diffusion inside the nanotubes is not described by a Ficḱs behavior. We report on the influence on water diffusion of various parameters such as length and concentration of CNTs, comparing the CG results with those obtained from the more accurate classic force field calculation, like the all-atom approach. Calculated water diffusion coefficients decreased in the presence of nanotubes in a concentration dependent manner. We also observed smaller water diffusion coefficients for longer CNTs. Using the CG methodology we were able to demonstrate anisotropic diffusion of water inside the nanotube scaffold, but we could not prove anisotropy in the surrounding medium, suggesting that grouping several water molecules in a single diffusing unit may affect the diffusional anisotropy calculated. The methodologies investigated in this work represent a first step towards the study of more complex models, including anisotropic cohorts of CNTs or even neuronal axons, with reasonable savings in computation time.     

Review: static and dynamic behavior of liquids inside carbon nanotubes

This review deals with the static and dynamic behavior of liquids inside carbon nanotubes, a broad subject, which includes: the investigation of liquid entering inside the tubes, and the subsequent filling of them, the overall flow through tubes as well as the wetting of the nanotube walls. Although most of the numerical work has been done on small diameter nanotubes, due to computational limitations, a large wealth of experimental results have been obtained for larger diameter nanotubes, between 10 and 100 nm, or above. This review offers an overview of the major achievements in the field, with particular emphasis on the effect on liquid flow through them of the structure and chemistry of carbon nanotubes. The limit below which liquids confined in nanotubes will not obey classical fluid dynamics equations as well as the structure and state of liquids under confinement will also be reviewed. Finally, near-to commercialization and still-in-the-lab applications will be covered.     

A comparison of neural networks and adaptive neuro-fuzzy inference systems for the prediction of water diffusion through carbon nanotubes

Given the fact that artificial intelligence tools such as neural network and fuzzy logic are capable of learning and inferencing from the past to capture the patterns that exist in the data, this study presents an intelligent method for the forecasting of water diffusion through carbon nanotubes where predictions are generated from neuro-fuzzy structures using molecular dynamics data. Therefore, this research was mainly focused on combining molecular dynamics with artificial intelligence methods in order to reduce the computational time of biomolecular and nanofluidic simulations. Two different artificial intelligence methods are applied for the time-dependent water diffusion forecasting: artificial neural network (ANN) and adaptive neuro-fuzzy inference systems (ANFISs). The effects of different sizes of training sample sets on forecasting performance of ANN and ANFIS are investigated as well. Four different evaluation methods are used to measure the performance and forecasting accuracy of these two methods. As a result, ANFIS presents the higher accuracy than neural network method based on the comparison of these different evaluation methods adopted in this research. The results reported in this research demonstrate that combining of molecular dynamics with artificial intelligence methods can be one of the most powerful and beneficial tools for prediction of important nanofluidic parameters.     

Prediction of the viscosity of water confined in carbon nanotubes

In this paper, the viscosity of water confined in single-walled carbon nanotubes (SWCNTs) with the diameter ranging from 8 to 54 ? is evaluated, which is crucial for the research on the nanoflow but difficult to be obtained. An “Eyring-MD” (molecular dynamics) method combining the Eyring theory of viscosity with the MD simulations is proposed to tackle the particular problems. For the critical energy which is a parameter in the “Eyring-MD” method, the numerical experiment is adopted to explore its dependence on the temperature and the potential energy. To demonstrate the feasibility of the proposed method, the viscosity of water at high pressure is computed and the results are in reasonable agreement with the experimental results. The computational results indicate that the viscosity of water inside SWCNTs increases nonlinearly with enlarging diameter of SWCNTs, which can reflect the size effect on the transports capability of the SWCNTs. The trend of the viscosity is well explained by the variation of the hydrogen bond of the water inside SWCNTs. A fitting equation of the viscosity of the confined water is given, which should be significant for recognizing and studying the transport behavior of fluid through the nanochannels.     

Manipulation and patterning of carbon nanotubes utilizing optically induced dielectrophoretic forces

This study reports an optically driven platform upon which the manipulation and patterning of carbon nanotubes (CNTs) can be accomplished. A photoconductive layer made of amorphous silicon generates a nonuniform electric field within the developed platform at specific optically illuminated sites, which are usually referred to as “virtual electrodes,” that induces dielectrophoretic forces for manipulating the CNTs. The software-controlled light patterns enable a variety of flexible manipulation modes since it is now possible to dynamically reconfigure the optically projected electrode patterns. This approach allows for real-time manipulation and miscellaneous patterning of CNTs. The sorting and separation of bundled and dispersed CNTs is also demonstrated. This developed platform may be promising for rapid fabrication of CNT-based nanosensors together with nanoelectronics, purification as well as classification of synthesized CNTs and other applications requiring nanoscale manipulation.     

Charge-tunable insertion process of carbon nanotubes into DNA nanotubes

Control over interactions with biomolecules holds the key of the applications of carbon nanotubes (CNTs) in biotechnology. Here we report a molecule dynamics study on the encapsulation process of different charged CNTs into DNA nanotubes. Our results demonstrated that insertion process of CNTs into DNA nanotubes are charge-tunable. The positive charged CNTs could spontaneously encapsulate and confined in the hollow of DNA nanotubes under the combination of electrostatic and vdW interaction in our ns scale simulation. The conformation of DNA nanotubes is very stable even after the insertion of CNTs. For pristine CNTs, it could not entirely encapsulated by DNA nanotubes in simulation scale in this study. The encapsulation time of pristine CNTs into DNA nanotubes was estimated about 21.9 s based on the potential of mean force along the reaction coordination of encapsulation process of CNTs into DNA nanotubes. In addition, the encapsulation process was also affected by the diameter of CNTs. These findings highlight the charge-tunable self-assembly process of nanomaterials and biomolecules. Our study suggests that the encapsulated CNTs-DNA nanotubes could be used as building blocks for constructing organic–inorganic hybrid materials and has the potential applications in the field of biosensor, drug delivery system and biomaterials etc.     

纳米碳管的若干动力学问题

以单壁纳米碳管为例,建立了其分子动力学模型,并对(5,5)和(10,10)扶手椅型纳米碳管与刚性壁的正碰撞过程和简谐纵波传播过程进行了模拟.在此基础上,探讨如何用弹性杆模型来研究纳米碳管的动力学问题。研究表明,弹性杆模型可以描述单壁扶手椅型纳米碳管与刚性壁高速碰撞的动力学行为;对于纵波传播中的色散描述,则需在弹性杆模型中计入纳米碳管微结构引起的非局部弹性效应.     

On radial breathing vibration of carbon nanotubes

The study aims at exploring the RBM (radial breathing mode) frequencies and mode shapes of various carbon nanotubes (CNTs) using a modified molecular structural mechanics (MSM) model. The focus of the work is placed upon studying the characteristics of the RBM-like modes of the CNTs resulted from their large diameter-length aspect ratio and/or asymmetric atomic configuration. By the approach, their dependence on the layer number, aspect ratio and chirality of the CNTs and temperature is also assessed. The validity of these calculated results is extensively confirmed through comparison with the literature theoretical and experimental data. Simulation results show that an additional layer of CNTs would not have significant impact on the associated RBM frequencies. In addition, asymmetric, non-purely radial RBM modes are observed in the chiral CNTs mainly because of their non-axisymmetric atomic structure. Besides, as the aspect ratio becomes larger than about 1.25, the original, standard RBM mode would be transformed into an RBM-like mode.     

多壁碳纳米管吸附鸟嘌呤的研究

用丝网印刷的方法在叉指电极上制备多壁碳纳米管膜,对碳纳米管吸附鸟嘌呤的电学性质进行了测试,对碳纳米管吸附鸟嘌呤的机理进行了初步分析。碳纳米管膜在吸附鸟嘌呤后电阻明显增大,用混酸修饰过的碳纳米管膜更敏感。其敏感率随着鸟嘌呤浓度的增大而增大。该膜在不同电流范围下性能基本稳定。这说明碳纳米管有望作为DNA传感器。     

Platinated ultrathin films made of carbon nanotubes

In this study a promising approach for a novel fuel cell catalyst layer is shown using films of carbon nanotubes (CNTs) formed by the layer-by-layer (LbL) method. A special focus is on the dispensing procedure of CNTs in water what is one of the most essential steps to realize monolayers in a reproducible way as targeted in LbL. Furthermore, the platination of the tubes is demonstrated using the reduction of platinum salt in ethylene glycol resulting in a sufficient distribution of nanosized particles. Finally, ultrathin films based on the functionalized nanotubes are investigated with atomic force microscopy, showing promising results for the future use as catalyst layer.     

Decomposition of nitrous oxide on carbon nanotubes

In this work, we have suggested the possibility of using carbon nanotubes to remove toxic gas. By taking an advantage of the density functional theory, we have investigated the decomposition of nitrous oxide (N(2)O) on the sidewalls of the perfect and the Stone-Wales defect armchair (5,5)-SWNTs at the B3LYP/6-31G(d) level of theory. There are two reaction mechanisms proposed: stepwise and concerted pathways. Our calculations predict that the former route is kinetically favored on both the perfect and defect SWNTs with barrier heights of the rate-determining steps of 37.23 and 34.38 kcal/mol for the perfect and the defect systems, respectively. In the second pathway, the decomposition of nitrous oxide gas takes place in a single step with higher reaction barriers of 48.60 and 40.27 kcal/mol on the sidewalls of the perfect and the defect SWNTs, respectively. Moreover, we also demonstrated that an encapsulation of electron rich species, such as chloride anion, inside the channel of the SWNT can boost up the reaction rate of the N(2)O decomposition on the SWNT. The chloride ion supplies excess electrons to the SWNT for transferring to the N(2)O molecule causing lower reaction barriers in the reaction pathways.     

Flexible vapour sensors using single walled carbon nanotubes

Thin, strongly adhering films of single-walled carbon nanotube bundles (SWNT) on flexible substrates such as poly(ethyleneterephthalate) (PET) were used for vapour sensing (hexane, toluene, acetone, chloroform, acetonitrile, methanol, water, etc.). These sensors are extremely easy to fabricate using the line patterning method. For example, ‘4-probe’ sensor patterns are drawn on a computer and then printed on overhead transparency (PET) sheets. These PET patterns were coated with films of electronically conductive SWNT bundles (1–2 μm thick) by dip-coating in aqueous surfactant-supported dispersions and mounted in glass chambers equipped for vapour sensing. Experiments conducted under saturated vapour conditions in air showed sensor responses that correlated well with solvent polarity [E_T(30) scale]. Similar results were obtained under controlled vapour conditions (no air) at 10,000 ppm. Control experiments using films of carbon black on PET (Aquadag-E^®), also prepared by the line patterning method, showed very little response to vapours under identical experimental conditions. The sensors are very flexible, e.g., they can be bent to diameters as small as 10 mm without significantly compromising sensor function.     

Dielectrophoretic separation of carbon nanotubes and polystyrene microparticles

The separation of multi-walled carbon nanotubes (MWCNTs) and polystyrene microparticles using a dielectrophoresis (DEP) system is presented. The DEP system consists of arrays of parallel microelectrodes patterned on a glass substrate. The performance of the system is evaluated by means of numerical simulations. The MWCNTs demonstrate a positive DEP behaviour and can be trapped at the regions of high electric field. However, the polystyrene microparticles demonstrate a negative DEP behaviour at a certain range of frequencies and migrate to the regions of low electric field. Experiments are performed on the microparticles at the frequencies between 100 Hz and 1 MHz to estimate their crossover frequency and select the range of separation frequencies. Further, experiments are conducted at the obtained range of separation frequencies to separate the MWCNTs and polystyrene microparticles.     

多壁碳纳米管半乳糖生物传感器研究

以普鲁士蓝(PB)膜玻碳电极为基质,用多壁碳纳米管固定半乳糖氧化酶(GAO),构造了半乳糖电流型传感器,研究了半乳糖氧化酶在此传感器中的催化反应机理,对多壁碳纳米管半乳糖传感器的检测条件进行了优化。确认其对半乳糖具有灵敏的生物响应性,表现出良好的线性和分辨力。此传感器对半乳糖摩尔浓度0.5×10-4~1.5×10-2mol/L呈线性响应,检出限为1.0×10-4mol/L,响应时间为10 s,30 d后,响应电流依然保持80%。     

Improving jet reactor configuration for production of carbon nanotubes

The jet mixing reactor has been proposed for the industrial production of fullerence carbon nanotubes. The goal is to obtain a uniformly high temperature of a catalyst. The mixing flowfield is studied using the semi-implicit method for pressure-linked equations revised algorithm. Hot peripheral jets are used to enhance heating of the central jet by mixing with the ambience of the reactor. Numerous configurations of peripheral jets with various numbers of jets, distance between nozzles, angles between the central jet and a peripheral jet, and twisted configuration of nozzles are considered. Unlike the previous studies of jet mixing, the optimal configuration of peripheral jets produces strong stretching of a cross-section of the central jet that enhances the mixing of the central jet with the reactor ambience.     

定向阵列碳纳米管在化学和生物传感器中的应用

定向阵列碳纳米管(ACNTs)作为一种新型的有序碳类材料,相比无序碳纳米管有更大的比表面积和促进电子的传递,因此能进一步提高其作为传感器的灵敏度.该文综述了定向阵列碳纳米管的制备方法和基于定向阵列碳纳米管的化学和生物传感器研究进展.     

碳纳米管在高电压设备在线监测领域的应用

阐述了高压电气设备绝缘故障在线检测的一些方法,介绍了碳纳米管气体传感器近期的研究动向和取得的成果。应用碳纳米管气体传感器监测电气设备绝缘故障特征气体时,重点介绍了纯SF6,SF6/N2混合气体中局部放电产生的气体分解组分在电压、气体压强、温度等因素下对气体传感器的影响。并提出了碳纳米管气体传感器在高电压设备在线检测领域研究中所存在的问题和未来的研究发展方向。