Transient electrohydrodynamic convective flow and heat transfer of MWCNT - Dielectric nanofluid in a heated enclosure

A computational research was performed to analyze the electrohydrodynamic (EHD) convective heat transfer in a differentially heated dielectric-MWCNT nanofluid layer. The study was conducted on a square enclosure subjected to a temperature gradient between these two vertical walls as well as a potential difference between these horizontal walls. The enclosure was filled with MWCNT oil-based nanofluid; the MWCNT nanoparticles were dispersed in a perfectly insulating thermal oil with a volume fraction of hardly exceeded 0.4%. The governing equations were derived with the assumption of homogeneous nanofluid and were solved with employing finite volume method. Based on the obtained results, it was found that the increase of Rayleigh number, electric Rayleigh number and nanoparticle concentration enhanced the heat transfer. For high thermal and electric Rayleigh number values, the flow and heat transfer became time dependent and accordingly a frequency study was also performed. It was found that the inclusion of an electric field with the addition of nanoparticles led to a significant heat transfer enhancement of about 43%.     

Synthesis of carbon nanotube‐based nanocomposite and application for wastewater treatment by ultrasonicated adsorption process

The sorption of methylene blue (MB) and basic yellow 28 (BY28) dyes in water on Ag@ZnO/MWCNT (Ag‐doped ZnO loaded on multiwall carbon nanotubes) nanocomposite is investigated in a batch process, optimizing starting initial dye concentration, sonication time and adsorbent mass. Isotherms and kinetic behaviours of MB and BY28 adsorption onto Ag@ZnO/MWCNT were explained by extended Freundlich and pseudo‐second‐order kinetic models. Ag@ZnO/MWCNT was synthesized and characterized using X‐ray diffraction, energy‐dispersive X‐ray spectroscopy, field emission scanning electron microscopy and Brunauer–Emmett–Teller analysis. According to the experimental data, adaptive neuro‐fuzzy inference system (ANFIS), generalized regression neural network (GRNN), backpropagation neural network (BPNN), radial basic function neural network (RBFNN) and response surface methodology (RSM) were developed, and applied to forecast the removal performance of the sorbent. The influence of process variables (i.e. sonication time, initial dye concentration, adsorbent mass) on the removal of MB and BY28 was considered by central composite rotatable design of RSM, GRNN, ANFIS, BPNN and RBFNN. The performances of the developed ANFIS, GRNN, BPNN and RBFNN models were compared with RSM mathematical models in terms of the root mean square error, coefficient of determination, absolute average deviation and mean absolute error. The coefficients of determination calculated from the validation data for ANFIS, GRNN, BPNN, RBFNN and RSM models were 0.9999, 0.9997, 0.9883, 0.9898 and 0.9608 for MB and 0.9997, 0.9990, 0.9859, 0.9895 and 0.9593 for BY28 dye, respectively. The ANFIS model was found to be more precise compared to the other models. However, the GRNN method is much easier than the ANFIS method and needs less time for analysis. So, it has potential in chemometrics and it is feasible that the GRNN algorithm could be applied to model real systems. The monolayer adsorption capacity of MB and BY28 was 292.20 and 287.02 mg g^?1, respectively.     

Influence of MWCNT on the properties of hydrogen bonded liquid crystals

A hydrogen bonded complex molded between p-n-octylbenzoicacid (8BA) and m-fluorobenzoic acid (FBA) is isolated and doped with predetermined quantity of Multi Walled Carbon Nano Tube (MWCNT) in order to achieve better thermal and electrical performance. The obtained series of liquid crystal nano systems comprising of three mesogens, varying in the weight percentage of MWCNT are analyzed by Polarizing Optical Microscope (POM), Differential Scanning Calorimetry (DSC) and Fourier Transform Infra-Red (FTIR) spectroscopy. Different aspects of the MWCNT – liquid crystal combination, evaluation of MWCNT's effect on selected properties of liquid crystals which are relevant to display related applications are discussed. In addition, Frederik's transitions of MWCNT dispersed liquid crystals reveal the direct effect of bundles of MWCNT on liquid crystal reorientation.     

不同参数多壁碳纳米管的拉曼光谱研究

拉曼光谱是进行碳材料结构与性质研究的有力手段,为了研究多壁碳纳米管(MWCNT)的管径和长度对其拉曼光学性质的影响,本研究对一系列不同管径和长度的多壁碳纳米管进行拉曼光谱的测试和分析。研究发现: 与高取向的石墨相比,多壁碳纳米管一阶拉曼光谱的G峰中心和D峰中心都会向低波数发生不同程度的红移;MWCNT两个主要特征峰(G峰和D峰)峰强在其他条件相同的情况下,与MWCNT的管径成正比,与长度成反比;G峰的频移与MWCNT的管径和长度两个因素密切相关,与管径成反比关系(这与单壁碳纳米管的径向呼吸模有着一致的结果),与管长成正比关系,而D 峰的频移受MWCNT的管径和长度的影响很弱,并对此现象进行了初步分析。在此基础上,我们以MWCNT的长径比为横坐标,G峰频移为纵坐标作图,进行线性拟合,得到了G峰频移与长径比成一定的线性递增关系。采用同样的分析方法,我们将G峰和D峰强度分别对MWCNT的长径比作图,进行线性拟合,得到了G峰和D峰强度分别与MWCNT的长径比成一定的线性递减关系。     

Sulfur cloaked with different carbonaceous materials for high performance lithium sulfur batteries

Carbon matrices have attracted the attention enthusiastically as the improver materials of sulfur for rechargeable lithium-sulfur battery. In this work, various morphologies (sphere, fiber, tube and layer) based carbon materials have been used for preparing the sulfur-carbon binary composites via melt diffusion method for lithium-sulfur battery application. The prepared binary composites have been characterized for its structural and morphological information using X-ray diffraction, Fourier transform infrared spectroscopy, Raman spectroscopy, and, Scanning and Transmission electron microscopy. The electrochemical studies are characterized by cyclic voltammetry, charge-discharge and cycle life after being assembled as lithium-sulfur cell. The S-prGO composite exhibits the initial discharge capacity of 893 mAh g⁻¹ and it sustains over 50 cycles (598 mAh g⁻¹) at 0.1C, with low capacity fading rate when compared to the other composites studied. A remarkable electrochemical performance indicates that the sheet like morphology can accommodate the volume expansion of sulfur and the oxygen groups containing GO minimize the dissolution of lithium polysulfides.     

Effect of multi-walled carbon nanotubes on dielectric and electro-optic properties of a high tilt antiferroelectric liquid crystal

By dispersing a small amount of multi-walled carbon nanotubes in a high tilt antiferroelectric liquid crystal, a nano composite is prepared. Though the phase sequence remains the same, the transition temperatures of the composite get changed, the stability of SmA* and SmC* phases increases whereas that of SmC_A* phase decreases. Pitch of the helicoidal structure shows a discontinuous change at SmC*–SmC_A* transition. Absorption strength and critical frequency of the anti-phase antiferroelectric mode are reduced in the composite. The dielectric increment of the Goldstone mode (GM) decreases and the critical frequency increases due to increased elasticity of the composite. A two-fold increase in the critical field for suppression of the GM is observed which signifies more stable helical structure in the composite. The switching time is reduced by 56% in the nano composite as a result of decrease in rotational viscosity but the high tilt remains intact. An observed lower value of conductivity indicates ion trapping in the composite.     

Significance of Darcy-Forchheimer Porous Medium in Nanofluid Through Carbon Nanotubes

This article manages Darcy-Forchheimer 3D flow of water based carbon nanomaterial (CNTs). A bidirectional nonlinear stretchable surface has been utilized to make the flow. Disturbance in permeable space has been represented by Darcy Forchheimer (DF) expression. Heat transfer mechanism is explored through convective heating. Outcomes for SWCNT and MWCNT have been displayed and compared. The reduction of partial differential framework into nonlinear common differential framework is made through reasonable variables. Optimal series scheme is utilized for arrangements advancement of associated flow issue. Optimal homotopic solution expressions for velocities and temperature are studied through graphs by considering various estimations of physical variables. Moreover surface drag coefficients and heat transfer rate are analyzed through plots.     

Characterization of carbon nanotubes and analytical methods for their determination in environmental and biological samples: A review

In the present paper, a critical overview of the most commonly used techniques for the characterization and the determination of carbon nanotubes (CNTs) is given on the basis of 170 references (2000–2014). The analytical techniques used for CNT characterization (including microscopic and diffraction, spectroscopic, thermal and separation techniques) are classified, described, and illustrated with applied examples. Furthermore, the performance of sampling procedures as well as the available methods for the determination of CNTs in real biological and environmental samples are reviewed and discussed according to their analytical characteristics. In addition, future trends and perspectives in this field of work are critically presented.     

Thermal and electrical behaviors of acid functionalized MWCNT/ABC-type triblock copolymer grafted-MWCNT nanocomposites

In this work, ABC-type triblock copolymer grafted onto the surface of the MWCNT/acid functionalized MWCNT (MWCNT-COOH) composites were prepared and the properties of nanocomposites were characterized extensively using differential scanning calorimetry (DSC), scanning electronic microscopy (SEM), thermogravimetric analysis (TGA), ac electrical conductivity and dielectrical measurements.

DSC study showed that the glass transition temperatures of the nanocomposites are a some higher than that of the matrix polymer. The increase in oxidized MWCNT in the nanocomposite improved the thermal stability of the composite, according to initial decomposition temperatures. The ac electrical conductivity has increased moderately with increasing frequency, but has increased slowly with increase in the oxidized MWCNT content in the nanocomposites. The electrical conductivity increases slowly with increasing temperature to about the glass transition temperature, then it increases faster. The dielectric constants for the matrix polymer and all the composites decreases slightly with increasing frequency from 0.1 kHz to 2.0 kHz. The dielectric constant increases slightly with increasing temperature up to about the glass transition temperature region and then the increase in temperature is accelerated the increase in the dielectric constant.     

UV and thermally stable polystyrene‐MWCNT superhydrophobic coatings

A facile method for ultraviolet (UV) and thermally stable polystyrene‐multiwalled carbon nanotubes (PS‐MWCNT) superhydrophobic coatings was demonstrated by a simple spray coating method. The superhydrophobicity was understood by an increase in micro/nano roughness with the addition of MWCNTs. Surface morphology of the coatings showed protrusion like structure. The wetting behavior of the coatings was studied as a function of temperature, and it is observed that the coatings were superhydrophobically stable up to 250 °C. A transformation of superhydrophobic to superhydrophilic state is achieved at 300 °C. The coatings remained superhydrophobically stable when it was subjected to UV‐irradiation and water immersion of 50 h. Thermogravimetric analysis showed a small shift (10°) towards higher temperature region with an addition of MWCNTs, suggesting the presence of weak interactions between PS and MWCNT, which is also supported by Fourier transform infrared spectroscopy, Raman and X‐ray photoelectron spectroscopy studies. Both hydrophilic and superhydrophobic coatings find potential applications in our daily life. Copyright © 2016 John Wiley & Sons, Ltd.