Superhydrophobicity on two-tier rough surfaces fabricated by controlled growth of aligned carbon nanotube arrays coated with fluorocarbon

Considerable effort has been expended on theoretical studies of superhydrophobic surfaces with two-tier (micro and nano) roughness, but experimental studies are few due to the difficulties in fabricating such surfaces in a controllable way. The objective of this work is to experimentally study the wetting and hydrophobicity of water droplets on two-tier rough surfaces for comparison with theoretical analyses. To compare wetting on micropatterned silicon surfaces with wetting on nanoscale roughness surfaces, two model systems are fabricated: carbon nanotube arrays on silicon wafers and carbon nanotube arrays on carbon nanotube films. All surfaces are coated with 20 nm thick fluorocarbon films to obtain low surface energies. The results show that the microstructural characteristics must be optimized to achieve stable superhydrophobicity on microscale rough surfaces. However, the presence of nanoscale roughness allows a much broader range of surface design criteria, decreases the contact angle hysteresis to less than 1 degrees , and establishes stable and robust superhydrophobicity, although nanoscale roughness could not increase the apparent contact angle significantly if the microscale roughness dominates.     

Growth Mechanism of Vertically Aligned Carbon Nanotube Arrays

Vertically aligned multi-walled carbon nanotube arrays grown on quartz substrate are obtained by co-pyrolysis of xylene and ferrocene at 850 oC in a tube furnace. Raman spectroscopy and high resolution transmission electron microscopy measurements show that the single-walled carbon nanotubes are only present on top of vertically aligned multi-walled carbon nanotube arrays. It has been revealed that isolated single-walled carbon nanotubes are only present in those floating catalyst generated materials. It thus suggests that the single-walled carbon nanotubes here are also generated by floating catalyst. Vertically alignedcarbon nanotube arrays on the quartz substrate have shown good orientation and good graphitization. Meanwhile, to investigate the growth mechanism, two bi-layers carbon nan-otube films with di erent thickness have been synthesized and analyzed by Raman spectroscopy. The results show that the two-layer vertically aligned carbon nanotube films grow “bottom-up”. There are distinguished Raman scattering signals for the second layer itself, surface of the first layer, interface between the first and second layer, side wall and bottom surface. It indicates that the obtained carbon nanotubes follow the base-growth mechanism, and the single-walled carbon nanotubes grow from their base at the growth beginning when iron catalyst particles have small size. Those carbon nanotubes with few walls (typically <5 walls) have similar properties, which also agree with the base-growth mechanism.     

Electrochemical Introduction of Active Sites into Super-long Carbon Nanotubes for Enhanced Capacitance

Electrochemical cyclic voltammetric(CV)scan was applied to inducing the partial oxidation and defects of carbon nanotubes(CNTs).The electrochemically induced functional groups and physical defects were...     

A study of the stability of aqueous suspensions of functionalized carbon nanotubes

The properties of aqueous suspensions of carbon nanotubes have been studied as depending on the conditions of their functionalization in a mixture of sulfuric and nitric acids. The elemental composition and contents of carboxyl, lactone, and hydroxyl groups in carbon nanotubes have been determined at different durations and temperatures of functionalization. The influence of functionalization conditions on the value of the electrokinetic potential of carbon nanotubes in aqueous suspensions and the nanotube solubility in water has been investigated. It has been found that the absolute value of the electrokinetic potential of nanotubes and their solubility in water increase with both the duration and temperature of functionalization due to a rise in the number of functional groups on their surface. The optimal regimes of functionalization of carbon nanotubes have been determined from the point of view of preserving their structure and stability in aqueous dispersions.     

Template Synthesis and Magnetic Behavior of FeNi Alloy Nanotube Arrays

"FeNi nanotubes were successfully prepared in pores of anodic aluminium oxide templates by the wetting template method. By varying the deposition conditions and the parameters of the templates, the lengths and the outer as well as the inner diameters of the tubes can be tailored. The FeNi nanotubes and their arrays were characterized by transmission and scanning electron microscopy. Macroscopic magnetic measurements show the FeNi nanotube arrays to have obvious anisotropy, and the easy axis is parallel to the nanotube axis. The magnetic moment distributions in the tube walls and the magnetization reversal mechanism are discussed. Magnetic moments of the FeNi nanotube preferentially lie in the nanotube wall, but the distribution is spatially isotropic. These magnetic behaviours are due to the unique shape of the nanotube."     

Self-assembly of linear arrays of semiconductor nanoparticles on carbon single-walled nanotubes

Ligand-stabilized nanocrystals (NCs) were strongly bound to the nanotube surfaces by simple van der Waals forces. Linear arrays of CdSe and InP quantum dots were formed by self-assembly using the grooves in bundles of carbon single-walled nanotubes (SWNTs) as a one-dimensional template. A simple geometrical model explains the ordering in terms of the anisotropic properties of the nanotube surface. CdSe quantum rods were also observed to self-organize onto SWNTs with their long axis parallel to the nanotube axis. This approach offers a route to the formation of ordered NC/SWNT architectures that avoids problems associated with surface derivatization.     

Charge transfer from metallic single-walled carbon nanotube sensor arrays

This paper explores the possibility of using arrays of metallic carbon nanotubes as sensors. Unlike their semiconducting counterparts, single-walled carbon nanotube arrays or networks that are dominated by metallic conduction pathways have not been investigated for their environmental sensitivity. In this work, we demonstrate transduction of molecular adsorption via charge transfer through predominantly metallic single-walled carbon nanotubes. Raman spectroscopy and electric field dependent transport confirm that signal transduction takes place through primarily large diameter metallic nanotubes. This unique signal transduction mechanism might have implications for novel sensors. The scaling of the signal with array impedance is well described using an irreversible binding model developed previously. The arrays have several advantages including a simple, two-electrode fabrication, rapid regeneration, and a responsivity that scales predictably and linearly with the number of adsorption sites. An array-assisted hydrolysis of reactive analytes is found to regenerate the nanotube surface from hydrolyzable species which include important organophosphate nerve agents.     

Ab initio simulations of doped single-walled carbon nanotube sensors

The interactions between oxygen and nitrogen atoms with single-walled carbon nanotubes were investigated for nanotubes with two different geometrical configurations using first-principle calculations within the framework of the density functional theory. We introduced a new type of toxic gas sensor that can detect the presence of H₂, Cl₂, CO, and NO molecules. We also demonstrated that the sensitivity of this device can be controlled by the concentration of the dopants on the surface of the nanotube. In addition, the transport properties of the doped nanotube were studied for different concentrations of oxygen or nitrogen atoms that were randomly distributed on the surface of the single-walled carbon nanotube. We observed that small amounts of dopants can modify the electronic and transport properties of the nanotube and can lend metallic properties to the nanotube. Band-gap narrowing occurs when the nanotube is doped with either oxygen or nitrogen atoms.     

The role of the medium in electrochemical functionalization and dispersion of carbon nanotubes

An electrochemical method for dispersion of single-walled carbon nanotubes (SWNTs) is described. The technique is based on grafting of oxygen-containing functional groups to the nanotube surface during electrolysis in aqueous and nonaqueous potassium bromide solutions. A dependence of the degree of functionalization of nanotubes on the solvent was revealed experimentally. Nanotubes treated in DMSO have about 14 carbon atoms per oxygen atom from functional groups (cf. nearly four C atoms per oxygen atom in the nanotubes treated in aqueous solutions). The corresponding maximum specific capacities of the electrodes are nearly 10 and 60 F g⁻¹. The samples treated in solutions of KBr in DMSO have about 300 carbon atoms per bromine atom on the nanotube surface (cf. only 30 carbon atoms in the samples treated in aqueous solution). A mechanism of electrochemical modification of SWNTs is proposed. Its key step is production of atomic oxygen that oxidizes the nanotube surface with the formation of functional groups.     

Fabrication of titania nanotube arrays on curved surface

In this paper, well-ordered titania nanotube arrays were formed on curved surface provided by titanium wire via anodic oxidation. The morphology of the nanotube arrays was observed by scanning electron microscopy (SEM). It was found that within the range of 360°, all the growing orientations of each nanotube keep correspondence with their outer electric fields. That is to say the surface shapes of anode play an important role on morphology of nanotube arrays. Compared with foils, by changing the anode shape, higher aspect ratio can be obtained. The nanotube arrays formed on wires can provide good understanding for the formation mechanism of the nanotube arrays. Furthermore, it can stimulate new thoughts in practical applications due to its ringed shaper.     

染料敏化的TiO2纳米管薄膜的光电浸润性

采用阳极氧化法在钛箔表面制备TiO2纳米管阵列, 并在其表面修饰N3染料(Ruthenium dye)作敏化剂, 用氟硅烷来提高表面疏水性, 获得超疏水薄膜. SEM测定结果表明, 纳米管薄膜具有各向异性浸润结构, 同时阳极氧化的非均匀性增加了表面的粗糙度. UV-Vis吸收光谱及电化学阻抗谱结果表明, 薄膜具有优异的光电性能. 通过施加超过一定阈值的电压, 液滴在薄膜表面由超疏水状态转变为亲水状态. 利用光电协同激励作用时, 阈值电压比单独使用电激励时降低了10 V, 这是使用高效的N3染料光电敏化层的结果.     

Effects of the HCN adsorption on the structural and electronic parameters of the beryllium oxide nanotube

The adsorption behavior of the HCN on the surface of beryllium oxide nanotube (BeONT) is studied by the density functional theory. Geometrical parameters, electronic properties and adsorption energies have been calculated for the BeONT and fourteen different HCN configurations on the nanotube. According to the obtained results, the process of the HCN molecule adsorption on different sites on the external surface of the nanotube is exothermic and all of the configurations are stable, while the process of HCN molecule adsorption on the internal surface of the BeONT is endothermic. The adsorption energy values indicate that the HCN molecule can be physically adsorbed on the surface of the BeONT. Furthermore, the HOMO–LUMO gap (Eg) of the BeONT decreases upon the HCN adsorption, resulting in the enhancement of the electrical conductivity. The AIM theory has been also utilized to analyze the properties of the bond critical points: their electron densities and their Laplacians. NBO analysis indicates that the HCN molecule can be adsorbed on the surface of the nanotube with a charge transfer from nanotube to HCN molecule. Due to the physisorption, NQR parameters of nanotube are also altered. In order to examine the deformation degree of the nanotube after HCN molecule adsorption, deformation energy is calculated, which indicates that no significant curvature in the geometry of the nanotubes is occurred when HCN adsorbs onto the surface of BeONT.     

Influence of polar groups on the wetting properties of vertically aligned multiwalled carbon nanotube surfaces

In this work, we have studied superhydrophilic and superhydrophobic transitions on the vertically aligned multiwalled carbon nanotube (VACNT) surfaces. As-grown, the VACNT surfaces were superhydrophobic. Pure oxygen plasma etching modified the VACNT surfaces to generate superhydrophilic behavior. Irradiating the superhydrophilic VACNT surfaces with a CO₂ laser (up to 50?kW?cm^?2) restored the superhydrophobicity to a level that depended on the laser intensity. Contact angle and surface energy measurements by the sessile drop method were used to examine the VACNT surface wetting. X-ray photoelectron spectroscopy (XPS) showed heavy grafting of the oxygen groups onto the VACNT surfaces after oxygen plasma etching and their gradual removal, which also depended on the CO₂ laser intensity. These results show the great influence of polar groups on the wetting behavior, with a strong correlation between the polar part of the surface energy and the oxygen content on the VACNT surfaces. In addition, the CO₂ laser treatment created an interesting cage-like structure that may be responsible for the permanent superhydrophobic behavior observed on these samples.     

湿法纯化碳纳米管阵列及其对碳纳米管阵列形貌的影响

采用酸溶液处理方法对垂直于衬底生长的碳纳米管阵列的纯化进行了研究. 利用扫描电子显微镜、X射线光电子能谱等手段对纯化前后的碳纳米管阵列的结构、形貌及化学组成进行表征. 实验结果表明, 通过控制条件, 酸溶液处理方法能够在有效地去除催化剂粒子等杂质的同时又保持阵列的相对完整性. 纯化后的碳纳米管阵列会促进其在电子学领域的进一步应用.     

Monodisperse rutile microspheres with ultrasmall nanorods on surfaces: Synthesis, characterization, luminescence, and photocatalysis

This work demonstrates the process of building optoelectrically cooperative surface wetting in smart and precise way. The superhydrophobic photosensitive film is constructed with TiO(2) nanotube arrays. Compared with conventional organic dyes, CdS quantum dots (QDs) as sensitizer layer are modified on TiO(2) nanotubes surface to improve photosensitivity of the composited surface in visible light region, which offer the benefit for designing and fabricating solid state hetero-junction devices. ITO glass is introduced as top electrode to apply electrical and optical stimuli and the patterned wetting is instantly obtained with masking light through ITO. The optoelectrically cooperative wettability conversion occurred on superhydrophobic TiO(2) nanotube surface at critical voltage of 12 V, which was decreased by 18 V comparing with only using electric stimulus. This study provides potential applications for TiO(2) nanotube arrays to the associated research of liquid reprography, location-controlled microfluidic device and lab-on-chip.     

Wet Purification of Aligned Carbon Nanotube Arrays and Its Impact on the Morphology of the Carbon Nanotube Arrays

A simple acid treatment method was applied to remove the catalyst impurities and other residues contaminated in the vertically aligned carbon nanotube arrays. We demonstrated that acid treatment was an efficient approach for aligned carbon nanotube purification. Scanning electron microscopy and X-ray photoelectron spectroscopy were used to characterize the morphology of the aligned carbon nanotube arrays and to determine the efficiency of the purification. Using hydrochloric acid could efficiently eliminate catalyst impurities and retain the original structures of the aligned carbon nanotube arrays. The method provided a simple, economical, and effective way to purify the aligned carbon nanotubes, and it would promote the applications of vertically aligned carbon nanotube arrays in electronic field.     

Capacitance response of double-walled carbon nanotubes depending on surface modification

The capacitive behaviors of high-purity double-walled carbon nanotubes (DWNTs) were investigated before and after oxidation using nitric acid (HNO₃). The electrodes prepared from the HNO₃-oxidized DWNTs have exhibited higher capacitances than the pristine nanotube electrode in both aqueous and non-aqueous systems, despite the deterioration of their specific surface area after HNO₃ oxidation. The superiority of the HNO₃-oxidized DWNTs in capacitance properties is caused by the variations of surface wettability and the interstitial pore structure of nanotube bundles, which result from the introduction of polar oxygen functional groups onto the nanotube surface by HNO₃ oxidation.     

超支化聚对氯甲基苯乙烯修饰碳纳米管表面的研究

用原子转移自由基聚合(ATRP)与自缩合乙烯基聚合(SCVP)相结合合成超支化聚合物聚对氯甲基苯乙烯(PCMS),该聚合物每个分枝均以卤素原子封端. 用叠氮化反应将卤素原子转换为—N3. 通过—N3与单壁或复壁碳纳米管反应将超支化聚合物接到碳纳米管的表面上, 实现了碳纳米管的化学修饰. 通过FTIR, XPS, TEM和Raman光谱等证明PCMS是以共价键形式结合到碳纳米管表面上的. 利用TGA估算出碳纳米管表面的修饰密度, 证明用超支化结构大量的端基可反应的官能团可以改善聚合物对碳纳米管的修饰效果.     

Diverse chemiresistors based upon covalently modified multiwalled carbon nanotubes

A diverse array of multiwalled carbon nanotube (MWCNT) sensory materials have been synthesized and used to create sensors capable of identifying volatile organic compounds (VOCs) on the basis of their functional groups. Functionalized MWCNTs with a series of cross-sensitive recognition groups were successfully synthesized via zwitterionic and post-transformation synthetic procedures. The incorporated chemical functional groups on MWCNT surfaces introduced greatly increased sensitivity and selectivity to the targeted analytes. The distinct response pattern of each chemical was subjected to statistical treatments, which led to a clear separation and accurate identification of 100% of the VOCs. These results demonstrate that covalent functionalized MWCNT-based sensor arrays are a promising approach for low-cost, real time detection and identification of VOCs.