Multi-walled Carbon Nanotubes Mass Research Articles

Effect of Different Preparation Parameters on the Stability and Thermal Conductivity of MWCNT-Based Nanofluid Used for Photovoltaic/Thermal Cooling

The thermal conductivity and stability of any nanofluid are essential thermophysical properties. These properties are affected by many parameters, such as the nanoparticles, the base fluid, the surfactant, and the sonication time used for mixing. In this study, multi-walled carbon nanotubes (MWCNTs) were selected as additive particles, and the remaining variables were tested to reach the most suitable nanofluid that can be used to cool photovoltaic/thermal (PVT) systems operating in the harsh summer conditions of the city of Baghdad. Among the tested base fluids, water was chosen, although ethylene glycol (EG), propylene glycol (PG), and heat transfer oil (HTO) were available. The novelty of the current study contains the optimization of nanofluid preparation time to improve MWCNTs’ PVT performance with different surfactants (CTAB, SDS, and SDBS) and base fluids (water, EG, PG, and oil). When 1% MWCNT mass fraction was added, the thermal conductivity (TC) of all tested fluids increased, and the water + nano-MWCNT advanced all TC (EG, PG, and oil) by 119.5%, 308%, and 210%, respectively. The aqueous nanofluids’ stability also exceeded the EG, PG, and oil at the mass fraction of 0.5% MWCNTs by 11.6%, 20.3%, and 16.66%, respectively. A nanofluid consisting of 0.5% MWCNTs, water (base fluid), and CTAB (surfactant) was selected with a sonication time of three and quarter hours, considering that these preparation conditions were practically the best. This fluid was circulated in an installed outdoor, weather-exposed PVT system. Experiments were carried out in the harsh weather conditions of Baghdad, Iraq, to test the effectiveness of the PVT system and the nanofluid. The nanofluid-cooled system achieved an electrical efficiency increase of 88.85% and 44% compared to standalone PV and water-cooled PVT systems, respectively. Additionally, its thermal efficiency was about 20% higher than that of a water-cooled PVT system. With the effect of the high temperature of the PV panel (at noon), the electrical efficiency of the systems was decreased, and the least affected was the nanofluid-cooled PVT system. The thermal efficiency of the nanofluid-cooled PVT system was also increased under these conditions. This success confirms that the prepared nanofluid cooling of the PVT system approach can be used in the severe weather of the city of Baghdad.

The influence of zinc phthalocyanine on the formation and properties of multiwalled carbon nanotubes thin films on the air–solid and air–water interface

The influence of zinc phthalocyanine (PC) on the formation and properties of multiwalled carbon nanotube (MWCNT) Langmuir films was studied. The mixtures of PC and MWCNT at different concentrations were prepared and used to obtain films on the air–solid and air–water interface. The excess Gibbs energy, excess areas and the area fraction covered by the mixtures components were determined for mixed systems at various surface pressures. For the mass fractions of MWCNT lower than 0.9, the interactions between the mixture components were attractive, while for the MWCNT mass fractions higher than 0.9, they were repulsive. Analysis of the area fractions and fluorescence images revealed three stages of filling the MWCNT films with PC. In the first stage, the PC filled the area between the MWCNT and started to form inclusions in the MWCNT film structure. In the second stage, gradual increase in the PC inclusion size with increasing PC concentration was observed. In the third stage, continuous PC films were formed. These observations were further confirmed by the calculation of electrical percolation threshold.

The Effect of Hydroxylated Multi-Walled Carbon Nanotubes on the Properties of Peg-Cacl2 Form-Stable Phase Change Materials

Calcium ions can react with polyethylene glycol (PEG) to form a form-stable phase change material, but the low thermal conductivity hinders its practical application. In this paper, hydroxylated multi-walled carbon nanotubes (MWCNTs) with different mass are introduced into PEG1500·CaCl2 form-stable phase change material to prepare a new type of energy storage material. Carbon nanotubes increased the mean free path (MFP) of phonons and effectively reduced the interfacial thermal resistance between pure PEG and PEG1500·CaCl2 3D skeleton structure. Thermal conductivity was significant improved after increasing MWCNTs mass, while the latent heat decreases. At 1.5 wt%, composite material shows the highest phase change temperature of 42 °C, and its thermal conductivity is 291.30% higher than pure PEG1500·CaCl2. This article can provide some suggestions for the preparation and application of high thermal conductivity form-stable phase change materials.

High-temperature liquid chromatography for evaluation of the efficiency of multiwalled carbon nanotubes as nano extraction beds for removal of acidic drugs from wastewater. Greenness profiling and comprehensive kinetics and thermodynamics studies

The retention behavior of a series of acidic drugs, namely ketoprofen (KET), naproxen (NAP), diclofenac (DIC), and ibuprofen (IBU), on the heat-resisting ZORBAX 300SB-C18 column, was studied thermodynamically using high-temperature liquid chromatography (HTLC). A perfect correlation of the compounds' lipophilicity and the calculated thermodynamic indicators evidenced its contribution to the retention behavior. Besides, the steric fitting has a subsidiary effect on IBU retention. Isocratic HTLC separation of the four compounds was achieved using an aqueous mobile phase containing 30% acetonitrile-0.2% acetic acid-0.2% triethylamine at 60 °C. This method has been utilized to monitor the adsorption efficiency of multiwalled carbon nanotubes (MWCNTs) for the removal of the four NSAIDs from water. Different variables affecting the remediation process have been optimized such as the time of contact, pH, ionic strength, temperature, and the mass of MWCNTs. The kinetics and thermodynamics of the adsorption were investigated. The adsorption was evidenced to take place via pseudo-second-order kinetics and the intraparticle diffusion is the rate-controlling step. The thermodynamic investigation showed that the adsorption process is exothermic and enthalpy-driven, and the adsorption is more extensive at a lower temperature. The MWCNTs showed excellent adsorption efficiency of about 76.4 to 97.6% at the optimum conditions. The obtained results are promising and encouraging for the full-scale application of MWCNTs for remediation of NSAIDs-related water pollution. The green analytical chemistry metric “AGREE” and the analytical eco-scale score tool confirmed that the developed protocol is greener and more favorable to the environment and user than most of the reported literature.

Влияние облучения ионами аргона на фильтрационные свойства многостенных углеродных нанотрубок

The wettability and filtration efficiency of multi-walled carbon nanotubes (MWCNT) under irradiation with Ar+ ions with an energy of 100 keV have been investigated. Energy dispersive X-ray spectroscopy, Raman spectroscopy, and scanning electron microscopy were used to study the residual manganese content in the filter, as well as to study the structure of irradiated MWCNTs. High fluence irradiated MWCNT (HR-MWCNT) filters showed an improvement in Mn removal of up to 99.6% at a Mn concentration of 10 ppm. HR-MWCNT based filters are extremely hydrophilic, with a 66° wetting angle and high absorption capacity. The efficiency of manganese removal from an aqueous medium has been studied as a function of pH, initial concentration, and mass of MWCNT.

Facile deposition of multiwalled carbon nanotubes via electrophoretic deposition in an environmentally friendly suspension

The present work focuses on the application of electrophoretic deposition (EPD) as a facile process to generate homogeneous layers of multi walled carbon nanotubes (MWCNTs) using water as an environmentally friendly solvent. The EPD process requires a pretreatment of the commercially available MWCNT powder to create a surface charge on the surfaces of the MWCNTs as well as to realize stable suspensions. After pre-treatment, the electrophoretic mobility of the MWCNTs was approximately μ ≈ − 4.3 · 10−4cm2V−1s−1 and the resulting ζ-potential is in the range of ζ ≈ −55 mV. The suspension showed no sedimentation over 50 days. The EPD was carried out at an applied voltage of 50 V. The MWCNTs were successfully deposited as open porous layers on gold as well as on aluminum. The specific double layer capacitance of the MWCNT-layers on gold amounts to C ≈ 11.9 Fg−1.However, on aluminum as substrate, the EPD of the MWCNTs is associated with the formation of a thin barrier like oxide film. In this case a major part of the applied voltage drops down across the oxide film and only a minor part across the suspension. Consequently, the field strength in the suspension decreases. Moreover, the capacitance of the oxide film dominates the whole capacitance of the electrode. The specific capacitance amounts to C = 0.3 mFg−1 related to the deposited mass of MWCNTs.

Development of Lightweight and High-Performance Ballistic Helmet Based on Poly(Benzoxazine-co-Urethane) Matrix Reinforced with Aramid Fabric and Multi-Walled Carbon Nanotubes.

This study aims to develop a lightweight ballistic helmet based on nanocomposite with matrix of the copolymer of benzoxazine with an urethane prepolymer [poly(BA-a-co-PU)], at mass ratio 80/20, reinforced with aramid fabric and multi-walled carbon nanotubes (MWCNTs). This has a protection level II according to the National Institute of Justice (NIJ) 0106.01 standard. The effects of MWCNTs mass content in a range of 0 to 2 wt% on tensile, physical and ballistic impact properties of the nanocomposite were investigated. The results revealed that the introduction of MWCNTs enhanced the tensile strength and energy at break of the nanocomposite; the highest values were obtained at 0.25 wt%. In addition, the nanocomposite laminate with 20 plies of aramid fabric showed the lowest back face deformation of 8 mm which was much lower than that specified by the NIJ standard. According to Military Standard (MIL-STD) 662F, the simulation prediction revealed that the ballistic limit of the ballistic helmet nanocomposite was as high as 632 m s−1. The developed laminates made of aramid fabric impregnated with poly(BA-a-co-PU) 80/20 containing 0.25 wt% MWCNTs showed great promise for use as a light weight and high-performance ballistic helmet.

Effect of MWCNT content and thickness of photoanode on microcracks in QDSCs

Multi-walled carbon nanotubes (MWCNTs) were introduced into titanium dioxide (TiO2) photoanode films in quantum dot sensitized solar cells (QDSCs) to modify the microcracks structure that produced during the sintering process. The effect of different mass fractions (0%, 0.01%, 0.05%, 0.1% and 0.3%) of MWCNTs and photoanode film thickness on the performance of QDSCs was investigated. BET test verified that MWCNTs after acid treatment possess a higher specific surface area. Above-mentioned photoanodes were sensitized with CdS/ZnS quantum dots (QDs) and then assembled to the QDSC sample with polysulfide electrolytes and CuS counter electrodes. The results showed that the cell with 0.05 wt% MWCNTs photoanode in 11.60 μm thickness exhibited the optimum photoelectric performance and its power conversion efficiency (PCE) increased by 73.3% compared with bare TiO2 photoanode QDSCs. The results of sensitized photoanodes microstructure characterization, electrochemical impedance (EIS) and current–voltage (J-V) curves were combined to investigate the synergetic effect of MWCNT mass fraction and photoanode film thickness on the photovoltaic performance of different QDSCs quantitatively.

Temperature self-regulating flat electric heaters based on MWCNTs-modified polymers

This article describes a technique for the manufacturing of the composites MWCNTs-modified elastomers. The effect of the different MWCNTs mass contents in the elastomer on specific volume and surface electrical resistivity values was investigated. The results on the heaters based on the elastomers and altered with multi-walled carbon nanotubes (MWCNTs) over various catalysts are discussed. It was found that with an increase in the MWCNTs mass content, the maximum power is achieved at a lower voltage value. Besides, temperature fields were measured on the surface of heater samples, and it was established that the temperature variation on the sample surface did not exceed 5 °C, and the heaters had a heating rate of 0.2–0.5 °C/s. Furthermore, a comparison of these heaters with the analogs previously reported by the other researchers is presented, indicating good importance of the reported work. The industrial (commercial) production of such devices is mainly associated with using in fan heaters for domestic purposes, in heaters built into clothes in underfloor heating systems and motor vehicles. The present work will find a good industrial application in the future.

Influence of preparation methods on the activity of macro-structured ball-milled MWCNT catalysts in the ozonation of organic pollutants

A series of macro-structured catalysts consisting of nanostructured layers of mechanically processed multiwalled carbon nanotubes (MWCNT) coated onto cordierite monoliths were prepared using a novel methodology and assessed as catalysts in the ozonation of a model organic pollutant. The often used chemical vapor deposition method for formation of nanostructured layers of carbon materials is, by nature, incompatible with ball-milling or other methods for mechanical or mechano-chemical modification of MWCNT. The preparation method here described was designed to translate the positive effect observed in the performance of ball-milled MWCNT as ozonation catalysts when compared with unmodified MWCNT to macro-structured catalytic systems. The performance of such macro-structured catalysts in the ozonation of organic pollutants is reported and analyzed for the first time. The effect of the preparation methodology, which includes physical functionalization of the MWCNT with a non-ionic surfactant (Triton X-100®), in the performance of the powder catalysts was evaluated. It was found that, for the coated nanostructured layers, the decrease in the expected activity is related to the packing of the materials. Nevertheless, the catalytic nanostructured coated layers were found to compare favorably with a reference sample. Thus, the beneficial effect of ball-milling MWCNT is still retained upon coating, even with a decrease in the intrinsic activity of the powder material. The increase in MWCNT mass in the coated samples introduces diffusion limitations, suggesting that creating a macroporous system in the MWCNT layers might be desirable. The introduction of oxygen-containing surface functionalities improved the long-term stability of the nanostructured catalytic layers.

Electrochemical detection of amyloid-β protein by delaminated titanium carbide MXene/multi-walled carbon nanotubes composite with molecularly imprinted polymer

Amyloid β-protein, a polypeptide, is known as the reason of neuronal death and is widely recognized as a biomarker of Alzheimer's disease. In this study, a simple and rapid electrochemical biosensor based on delaminated titanium carbide MXene (d-Ti3C2TX MXene) and multi-walled carbon nanotubes (MWCNTs) composite including molecularly imprinted polymers (MIPs) was formed for amyloid-β having 42-amino-acid-peptide (Aβ42) protein sensing. After d-Ti3C2TX/MWCNTs composite was prepared by mixing the colloidal solution of d-Ti3C2TX MXene with MWCNTs (mass ratio 3:1), some analytic methods such as x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), UV/Vis spectroscopy, atomic force microscopy (AFM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were performed for characterizations of d-Ti3C2TX MXene, MWCNTs and d-Ti3C2TX/MWCNTs composite. Later, Aβ42 imprinted d-Ti3C2TX/MWCNTs/GCE was prepared in a mixture including 100.0 mM pyrrole (monomer) containing 25.0 mM Aβ42 (template) in phosphate buffer (0.1 M, pH 7.5) by CV method for 25 cycles. Aβ42 imprinted electrode showed a linear range of 1.0 fg mL−1 - 100.0 fg mL-1 and detection limit (LOD) of 0.3 fg mL-1 were obtained. Aβ42 imprinted electrode was examined in terms of stability, repeatability, reproducibility and reusability. Finally, Aβ42 imprinted biosensor was applied to plasma samples for Aβ42 analysis.

Enhanced removal of Ni(II) from aqueous solutions by effective acid functionalization of carbon nanotube based filters

Multiwalled carbon nanotubes (MWNTs) have shown a promising efficiency as an adsorbent, owing to their large surface area and affinity for heavy metal ions. Nevertheless, the effective functionalization of the MWNT is essential to enhance the surface reactivity towards heavy metal removal. In order to elucidate this functionalization, acid treatment of mixture of HNO3/H2SO4 followed by H2SO4/H2O2 for etching process was conducted. The acid functionalized MWNTs (F-MWNTs) were characterized with SEM, EDS, BET surface area and FTIR. The obtained results confirm the formation of oxygen groups attached to the surfaces of treated nanotubes (e.g. carboxyl) which alter their physicochemical properties and enhance the surface reactivity. The removal of Ni(II) from aqueous solutions by using immaculate and functionalized MWNT-filters (F-MWNTs) was studied as a function of pH, initial concentration of Ni(II), MWNT mass and contact time. F-MWNT filters showed an enhancement of the removal efficiency of Ni(II) up to 99.8% for concentration 10 ppm with exceptionally high adsorption capacity that could reach 333.3 mg/g. The adsorption isotherm is well fitted by the Langmuir equation. The ion exchange mechanism between F-MWNTs and Ni(II) ions is suggested as well-situated mechanism. It was found that F-MWNT filters can be reused through many cycles of regeneration with high performance. Our investigation demonstrated that F-MWNT filters are effective and can be appreciably considered as resourceful and economical adsorbent for heavy metal removal from wastewater.

Rapid and versatile pre-treatment for quantification of multi-walled carbon nanotubes in the environment using microwave-induced heating

The concerns regarding potential environmental release and ecological risks of multi-walled carbon nanotubes (MWCNTs) rise with their increased production and use. As a result, there is the need for an analytical method to determine the environmental concentration of MWCNTs. Although several methods have been demonstrated for the quantification of well-characterized MWCNTs, applying these methods to field samples is still a challenge due to interferences from unknown characteristics of MWCNTs and environmental media. To bridge this gap, a recently developed microwave-induced heating method was investigated for the quantification of MWCNTs in field samples. Our results indicated that the microwave response of MWCNTs was independent of the sources, length, and diameter of MWCNTs; however, the aggregated MWCNTs were not able to convert the microwave energy to heat, making the method inapplicable. Thus, a pre-treatment process for dispersing bundled MWCNTs in field samples was crucial for the use of the microwave method. In the present paper, a two-step pre-treatment procedure was proposed: the aggregated MWCNTs loaded environmental samples were first exposed to high temperature (500°C) and then dispersed by using an acetone-surfactant solution. A validation study was performed to evaluate the effectiveness of the pre-treatment process, showing that an 80-120% recovery range of true MWCNT loading successfully covered the microwave-measured MWCNT mass.

Enhancement of CNT-based filters efficiency by ion beam irradiation

It is shown in the report that disorder produced by ion beam irradiation can enhance the functionality of the carbon nanotubes. The filters of pressed multiwalled carbon nanotubes (MWNTs) were irradiated by He+ ions of the energy E = 80keV with the fluence 2 × 1016ion/cm2. The removal of manganese from aqueous solutions by using pristine and ion beam irradiated MWNTs filters was studied as a function of pH, initial concentration of manganese in aqueous solution, MWNT mass and contact time. The filters before and after filtration were characterized by Raman (RS) and energy dispersive X-ray spectroscopy (EDS) techniques to investigate the deposition content in the filter and defect formation in the MWNTs. The irradiated samples showed an enhancement of removal efficiency of manganese up to 97.5% for 10ppm Mn concentration, suggesting that irradiated MWNT filter is a better Mn adsorbent from aqueous solutions than the pristine one. Radiation-induced chemical functionalization of MWNTs due to ion beam irradiation, suggesting that complexation between the irradiated MWNTs and manganese ions is another mechanism. This conclusion is supported by EDS and RS and is correlated with a larger disorder in the irradiated samples as follows from RS. The study demonstrates that ion beam irradiation is a promising tool to enhance the filtration efficiency of MWNT filters.

Hot‐melt adhesives based on co‐polyamide and multiwalled carbon nanotubes

ABSTRACTComposites of two hot melt adhesives based on co‐polyamides, one high viscosity (coPA_A), the other low viscosity (coPA_B), and multiwalled carbon nanotubes (MWCNTs) were prepared using twin‐screw extrusion via dilution of masterbatches. Examination of these composites across the length scales confirmed that the MWCNTs were uniformly dispersed and distributed in the polymer matrices, although some micron size agglomerations were also observed. A rheological percolation was determined from oscillatory rheology measurements at a mass fraction of MWCNTs below 0.01 for coPA_B and, between 0.01 and 0.02 for coPA_A. Significant increases in complex viscosity and storage modulus confirmed the “pseudo‐solid” like behavior of the composite materials. Electrical percolation, determined from dielectric spectroscopy was, found to be at 0.03 and 0.01 MWCNT mass fraction for coPA_A and coPA_B based composites, respectively. Addition of MWCNTs resulted in heterogeneous nucleation and altered the crystallization kinetics of both copolymers. Indirect evidence from contact angle measurements and surface energy calculations confirmed that MWCNT addition enhanced the adhesive properties of coPA_B to a level similar to coPA_A. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 45999.

Multiwalled carbon nanotubes twined α-nickel hydroxide microspheres as high-efficient urea electrooxidation catalysts

Multiwalled carbon nanotube (MWCNT) twined α-Ni(OH)2 microspheres, denoted as α-Ni(OH)2@MWCNT, are synthesized by a facile solvothermal method and are developed as a remarkably active catalyst for urea electrooxidation in alkaline media. Through optimizing the mass ratio between α-Ni(OH)2 and MWCNT, it is found that α-Ni(OH)2@MWCNT catalyst with a weight ratio of 2.5:1 affords the highest current density of 2503 mA cm−2 mg−1 at the potential of 0.58 V versus Hg/HgO and the largest exchange current density of 1.49 × 10−4 mA cm−2 among all the studied catalysts, which are much higher than that of pure α-Ni(OH)2 microspheres and are about one order of magnitude higher than that of reported Ni(OH)2 nanosheets. Additionally, the α-Ni(OH)2@MWCNT catalysts also present superior durability than pure α-Ni(OH)2. The exceptional catalytic performance of α-Ni(OH)2@MWCNT catalysts is attributed to the good electronic transport of MWCNT and favorable mass transport facilitated by α-Ni(OH)2 hollow porous microspheres. These results suggest the feasibility of an easy and low-cost solvothermal method to develop high-efficient catalyst for urea electrooxidation. Bird-nest-like microspheres of α-Ni(OH)2@MWCNT catalyst were synthesized with MWCNT twined α-Ni(OH)2 ultrathin nanosheets by an economical solvothermal method.

Effects of multiwalled carbon nanotube mass fraction on microstructures and electrical resistivity of polycarbonate-based conductive composites

AbstractFour polycarbonate (PC)-based composites with 1, 2.5, 5, and 10 wt.% raw multiwalled carbon nanotubes (MWCNTs) were prepared using extrusion process followed by injection molding. The effects of MWCNT mass fraction (W) on composite mechanical, thermal, and electrical properties were examined. The mechanical properties suggested that the tensile strength of the composites with 2.5 wt.% raw MWCNTs exhibited an increase of ~5 MPa (~8.6%) at a particular injection condition. Besides, thermogravimetric analysis (TGA) indicated that the addition of 1 wt.% MWCNTs improved the thermal stability of PC by approximately 100°C. Aside from mechanical and thermal properties, the electrical resistivity of the 5 wt.% raw MWCNT composites was considerably decreased to 102 Ω/sq, a value approximately 15 orders of magnitude lower than that of PC. Furthermore, the effects of injection conditions on composite electrical properties were emphatically discussed, and it was found that electrical resistivity was sensitive to injection temperature and speed. Low electrical resistivity was achieved at high injection temperature and low injection speed. Scanning electron microscopy images revealed that electrical resistivity relied on the microstructure of the prepared MWCNT/PC composites.

Roles of cation valance and exchange on the retention and colloid-facilitated transport of functionalized multi-walled carbon nanotubes in a natural soil

Saturated soil column experiments were conducted to investigate the transport, retention, and release behavior of a low concentration (1 mg L−1) of functionalized 14C-labeled multi-walled carbon nanotubes (MWCNTs) in a natural soil under various solution chemistries. Breakthrough curves (BTCs) for MWCNTS exhibited greater amounts of retardation and retention with increasing solution ionic strength (IS) or in the presence of Ca2+ in comparison to K+, and retention profiles (RPs) for MWCNTs were hyper-exponential in shape. These BTCs and RPs were well described using the advection-dispersion equation with a term for time- and depth-dependent retention. Fitted values of the retention rate coefficient and the maximum retained concentration of MWCNTs were higher with increasing IS and in the presence of Ca2+ in comparison to K+. Significant amounts of MWCNT and soil colloid release was observed with a reduction of IS due to expansion of the electrical double layer, especially following cation exchange (when K+ displaced Ca2+) that reduced the zeta potential of MWCNTs and the soil. Analysis of MWCNT concentrations in different soil size fractions revealed that >23.6% of the retained MWCNT mass was associated with water-dispersible colloids (WDCs), even though this fraction was only a minor portion of the total soil mass (2.38%). More MWCNTs were retained on the WDC fraction in the presence of Ca2+ than K+. These findings indicated that some of the released MWCNTs by IS reduction and cation exchange were associated with the released clay fraction, and suggests the potential for facilitated transport of MWCNT by WDCs.

Electric-field alignment of aqueous multi-walled carbon nanotubes on microporous substrates

Carbon nanotube membranes and polymer composites are used in a wide range of applications including flexible electronics, energy storage devices, and water treatment. Here, we present a method to produce a dense network of regionally aligned multi-walled carbon nanotubes (MWCNT) on the surface of microporous substrates using a combination of electric field alignment and vacuum filtration. The effect of electric field strength (0–22 Vrms mm−1), MWCNT concentration (0.002–0.01 wt% in water), and sample volume (0.025–0.150 mL) on the degree of alignment was examined. Qualitatively, increasing both electric field strength and MWCNT concentration resulted in an increase in differential resistance between the aligned and non-aligned directions. To quantitatively analyze the data, a statistical regression model was developed. The model indicates there is a quadratic dependence of MWCNT alignment with the strength of the electric field, MWCNT concentration, and total MWCNT mass. The best alignment within the experimental parameter space was achieved using 0.25 mL of 0.01 wt% MWCNT at an electric field strength of 22 Vrms mm−1; the log-ratio of resistance was 0.8.

Lightweight and Anisotropic Porous MWCNT/WPU Composites for Ultrahigh Performance Electromagnetic Interference Shielding

Lightweight, flexible and anisotropic porous multiwalled carbon nanotube (MWCNT)/water‐borne polyurethane (WPU) composites are assembled by a facile freeze‐drying method. The composites contain extremely wide range of MWCNT mass ratios and show giant electromagnetic interference (EMI) shielding effectiveness (SE) which exceeds 50 or 20 dB in the X‐band while the density is merely 126 or 20 mg cm−3, respectively. The relevant specific SE is up to 1148 dB cm3 g−1, greater than those of other shielding materials ever reported. The ultrahigh EMI shielding performance is attributed to the conductivity of the cell walls caused by MWCNT content, the anisotropic porous structures, and the polarization between MWCNT and WPU matrix. In addition to the enhanced electrical properties, the composites also indicate enhanced mechanical properties compared with porous WPU and CNT architectures.