Screening Electromagnetic Interference Effect using Nanocomposites

Summary: We carried out a systematic study of the electrical properties of carbon nanotube-based polymeric composite materials. Our purpose was the production and characterization of a light, thin and mechanically strong new composite material able to cover electric circuits against external electromagnetic interference. As polymeric matrix we used a commercial Shell product Epon 828 epoxy resin. Two types of curing agent were used along with the resin, namely A1 and PAP8 agent: the composite was obtained using the A1 curing agent, selected for the stability of the corresponding material over a wide range of pressure values. Setting the resistivity properties of carbon nanotube-based composites against those containing micro-sized graphite particles as constituent we showed the advantages of using carbon nanotubes. The change in the resistivity values for carbon nanotubes-based composites turned out to be significant, even for small changes in the added carbon nanotubes percentage. We also plan to show the composite's behavior in controlled humidity environments and for different temperatures. These results might be important for determining the most suitable “recipe” for the realization of composite materials useful to high-fidelity circuits applications, or even in devices exposed to predominantly electromagnetic noise.     

Nanofibrilar Polyaniline: Direct Route to Carbon Nanotube Water Dispersions of High Concentration

Water dispersible nanofibrilar polyaniline (NF‐PANI) provides a novel and direct route towards carbon nanotube water dispersions of high concentration. Carrying out the chemical synthesis of NF‐PANI in the presence of carbon nanotubes (CNTs) results in an entirely nanostructured nanofibrilar polyaniline/carbon nanotube (NF‐PANI/CNT) composite material that contains well segregated CNTs partially coated by NF‐PANI. This new approach is simple, fast, and inexpensive, and enables the direct preparation of stable and homogeneous dispersions of the composites in water at concentrations up to 10 mg · mL⁻¹, even for the highest CNT loadings of 50 wt.‐% without the participation of surfactants or stabilizers.

     

Photocatalytic Activity of Nanocomposites of ZnO and Multi-Walled Carbon Nanotubes for Dye Degradation

Nanocomposites of ZnO and multi-walled carbon nanotubes (MWNTs) were prepared via electrostatic interaction and in situ hydrothermal synthesis approaches. The ZnO/MWNTs nanocomposites display relatively higher photocatalytic activity than ZnO nanoparticles for the degradation of Rhodamine B. Therein, MWNTs, acting as a photogenerated electron acceptor, retard the recombination of photoinduced electron and hole. The experimental results show that the photocatalytic activity of the ZnO/MWNTs nanocomposites strongly depends on the synthetic route, which is probably due to the difference of surface states resulted from the different preparation processes.     

新型沥青基ACNT/C纳米复合材料的制备与表征

以超长定向碳纳米管(ACNTs)阵列为骨架，中温煤焦油沥青为浸渍剂，采用浸渍-炭化工艺经过一个循环制备了密度约为1.25 g·cm^-3的沥青基定向碳纳米管/炭(ACNT/C)纳米复合材料。采用扫描电子显微镜(SEM)、偏光金相显微镜(PLM)、X射线衍射(XRD)和Raman光谱分析对这种新型纳米炭材料进行了表征。结果表明ACNT/C中沥青炭为明显的各向异性组织，以碳纳米管为核心形成了非常细密的流线型层片结构，具有较高的晶化程度。采用热失重分析(TGA)方法考察了材料在空气中的热稳定性能，发现ACNT/C纳米复合材料在空气中的热失重初始温度比相同工艺条件下，以炭纤维为骨架制备的密度相近的炭/炭(C/C)复合材料提高了50 ℃左右。     

无机层状纳米材料与聚苯胺的复合研究

聚苯胺被认为是最有希望在实际中得到广泛应用的导电聚合物，通过与无机层状纳米材料的复合改性，其复合物在二次电池电解质、光电转换、热电、磁电、电致流变等新材料领域显示出诱人前景。本文对无机层状材料与聚苯胺的复合方法、复合物性质及其应用前景进行了评述。     

High‐Efficiency Encapsulation of Pt Nanoparticles into the Channel of Carbon Nanotubes as an Enhanced Electrocatalyst for Methanol Oxidation

Pt‐based nanostructures serving as anode catalysts for the methanol oxidation reaction (MOR) have been widely studied for many years. Nevertheless, challenging issues such as poor reaction kinetics and the short‐term stability of the MOR are the main drawbacks of such catalysts and limit their applications. Herein, we have developed a facile approach to encapsulate Pt nanoparticles (NPs) inside the nanochannels of porous carbon nanotubes (CNTs; Pt‐in‐CNTs) as a new enhanced electrocatalytic material. The as‐prepared CNTs offer simultaneously ordered diffusion channels for ions and a confinement effect for the NPs, which both facilitate the promotion of catalytic kinetics and avoid the Ostwald ripening of Pt NPs, thus leading to high activity and durable cycle life as an anode catalyst for MOR. This work provides a new approach for enhancing the stability and activity by optimizing the structure of the catalyst, and the Pt‐in‐CNTs represent the most durable catalysts ever reported for MOR.     

Polymer Layered Silicate/Carbon Nanotube Nanocomposites: Morphological and Rheological Properties

Morphological and rheological properties of new ternary nanocomposites based on ethylene vinyl acetate copolymers (EVA), commercial organo-modified clays (organoclays) and purified multi-walled carbon nanotubes (MWNTs), prepared via direct melt blending, have been evaluated. For sake of comparison, the corresponding binary compositions, i.e., EVA filled with either organoclays or MWNTs, have been investigated as well. While extensive exfoliation can be observed for binary EVA/clay nanocomposites, the addition of MWNTs appears to limit clay exfoliation. Rheological properties show that both clay and MWNTs increase the elastic modulus of the nanocomposites, reflecting the high degree of nanoparticle interconnectivity that can be found in these materials.     

Creep Resistant Polymer Nanocomposites Reinforced with Multiwalled Carbon Nanotubes

Poly(propylene) (PP) nanocomposites filled with shorter‐ and longer‐aspect‐ratio multiwalled carbon nanotubes (MWNTs) were compounded using a twin‐screw extruder and an injection moulding machine. It is shown that with only 1 vol.‐% of MWNTs, creep resistance of PP can be significantly improved with reduced creep deformation and creep rate at a long‐term loading period. Additionally, the creep lifetime of the nanocomposites has been considerably extended by 1 000% compared to that of a neat PP. Three possible mechanisms of load transfer were considered that could contribute to the observed enhancement of creep resistance, which are: (1) fairly good interfacial strength between MWNTs and polymer matrix, (2) increasing immobility of amorphous regions due to nanotubes acting as restriction sites, and (3) high aspect ratio of MWNTs. DSC results showing crystallinity changes in the specimens before and after creep deformation present evidence to confirm these mechanisms. Our results should lead to improved grades of creep resistant polymer nanocomposites for engineering applications.

     

Ternary composites of multi-wall carbon nanotubes,polyaniline, and noble-metal nanoparticles for potential applications in electrocatalysis

Multi-wall carbon nanotubes were coated with a conducting polymer, polyaniline phosphotungstate. Such composite structures have mixed electronic and proton conductivity, high surface area and porosity. These materials were decorated with catalytically-active noble metals — Pt, Pd, and Rh. Metal nanoparticles were uniformly distributed in the polymer matrix. Such ternary composites can be considered as electrode materials in sensors, electrolysers, supercapacitors, and especially in low-temperature fuel cells with a proton-conducting polymer membrane.     

Thermomechanical Properties of Carbon Nanocomposites PEGDA Photopolymers

In this work, UV-curable resin poly (ethylene glycol) diacrylate (PEGDA) was reinforced with three different types of nanofillers: pristine graphene (G), multiwalled carbon nanotubes (MWNTs), and a hybrid of MWNTs and graphene 70/30 in mass ratio (Hyb). PEGDA was mixed homogenously with the nanofiller oligomer by shear mixing and then photopolymerized, affording thin, stable films. The thermomechanical properties of the afforded nanocomposites indicated the superior reinforcing ability of pristine graphene compared with MWNTs and an intermediate behavior of the hybrid.     

反胶束体系中合成聚苯胺-无机物复合纳米微粒

利用阴离子型表面活性剂2-乙基己基琥珀酸钠(AOT)形成的反胶束作为微反应器合成了聚苯胺-氯化银和聚苯胺-硫酸钡复合纳米粒子;考察了搅拌因素和不同合成步骤对聚苯胺-硫酸钡尺寸及形态的影响;并利用TEM, IR, UV-vis, XRD和四探针电导率仪对产物进行了表征.研究结果表明,反胶束法可以有效地应用于有机-无机复合纳米材料的制备.     

Microwave Synthetic Routes for Shape-Controlled Catalyst Nanoparticles and Nanocomposites

The use of microwave irradiation for the synthesis of inorganic nanomaterials has recently become a widespread area of research that continues to expand in scope and specialization. The growing demand for nanoscale materials with composition and morphology tailored to specific applications requires the development of facile, repeatable, and scalable synthetic routes that offer a high degree of control over the reaction environment. Microwave irradiation provides unique advantages for developing such routes through its direct interaction with active reaction species, which promotes homogeneous heat distribution, increased reaction rates, greater product quality and yield, and use of mild reaction conditions. Many catalytic nanomaterials such as noble metal nanoparticles and intricate nanocomposites have very limited synthetic routes due to their extreme temperature sensitivity and difficulty achieving homogeneous growth. This work presents recent advances in the use of MW irradiation methods to produce high-quality nanoscale composites with controlled size, morphology, and architecture.     

In Situ Polymerized Carbon Nanotube/Polyimide Nanocomposites: Effect of Reaction Stoichiometry on the Glass Transition Properties of the Nanocomposites

A series of in situ polymerized CNT/PI nanocomposite materials synthesized at a fixed diamine‐to‐dianhydride monomer feed ratio with varying concentrations of added –COOH‐ functionalized CNT is studied. It is found that the glass transition temperature of the nanocomposite varies non‐monotonically with CNT concentration. To determine the origin of this behavior, the molecular weights of the matrix polymers are measured by the intrinsic‐viscosity method. The functional‐group density of the CNT material is determined by potentiometric titration. The results confirm that the glass transition of the CNT/PI system depends on the concentration of the CNT filler through its influence on the functional group stoichiometry and thus on the molecular weight of the polycondensation product.

     

Numerical Simulations of the Effect of Microstructure on AC Conductivity of MWCNT/Polymer Nanocomposites

A continuum model is developed to investigate the microstructure‐dependent AC properties of MWCNT/polymer nanocomposites. The AC conductivity of the composite is increased by a higher curl ratio of MWCNTs. At a critical frequency ω₀, the AC conductivity switches to a frequency‐dependent region. For high MWCNT content, the curl curliness of MWCNTs has only a weak influence on the AC conductivity. For medium MWCNT content, the AC conductivity became frequency‐dependent for low frequencies with decreasing curl ratio of MWCNTs, which cannot be explained by correlation length theory. An interpretation based on the linear circuit theory is given. With increasing size of MWCNT clusters, the critical frequency ω₀ increases. It is also affected significantly by the crystallinity the polymer.

     

Highly active electrocatalysis by cobalt tetraphenylporphyrin incorporated in a Nafion membrane for proton reduction

Electrocatalytic H⁺ reduction was studied with cobalt tetraphenylporphyrin (CoTPP) incorporated in a Nafion membrane coated on a Pt electrode (denoted as Pt/Nf[CoTPP]). It was found that Pt/Nf[CoTPP] shows an efficient catalytic activity to produce H₂ around the theoretical H⁺/H₂ redox potential (−0.25 V v. Ag/AgCl in a pH 1.01 aqueous solution), and that its catalytic activity is remarkably higher than a neat CoTPP film and a conventional Pt catalyst. The amount of the H₂ produced decreased with increasing CoTPP concentration in the membrane ([CoTPP]_Nf]). The ratio of electroactive Co^IITPP was independent of its concentration, showing that the present electron transfer process takes place via physical diffusion of the molecule. The intrinsic turnover number (TN_int) of the CoTPP to produce H₂, based on the electroactive amounts of the CoTPP, decreased with increasing [CoTPP]_Nf. The catalysis was discussed in terms of the characteristic of the Nafion membrane. © 1998 John Wiley & Sons, Ltd.     

Rapid functionalization of carbon nanotube and its electrocatalysis

It was reported that carbon nanotube (CNT) was functionalized with the electroactive Nile blue (NB), which is a phenoxazine dye, by a method of adsorption to form a NB-CNT nanocomposite. The NB-CNT nanocomposite was characterized by several spectroscopic techniques, for example, Ultraviolet-visible spectroscopy (UV-VIS), Fourier transform infrared (FTIR), Raman spectroscopy and scanning electron microscopy (SEM) etc., and the results showed that NB could rapidly and effectively be adsorbed on the surface of CNT with a high stability without changing the native structure of NB and the structure properties of CNT. Moreover, it was shown that the dispersion ability of CNT in aqueous solution had a significantly improvement after CNT functionalized with NB even at a level of high concentration, for example, 5 mg of NB-CNT per 1 mL of H₂O. The NB-CNT/ glasssy carbon (GC) electrode was fabricated by modifying NB-CNT nanocomposite on the GC electrode surface and its electrochemical properties were investigated by cyclic voltammetry. The cyclic voltammetric results indicate that CNT can improve the electrochemical behavior of NB and greatly enhance its redox peak currents. While the NB-CNT/GC electrode exhibited a pair of well-defined and nearly symmetrical redox peaks with the formal potential of (−0.422±0.002) V (versus SCE, 0.1 mol/L PBS, pH 7.0), which was almost independent on the scan rates, for electrochemical reaction of NB monomer; and the redox peak potential of NB polymer located at about −0.191 V. The experimental results also demonstrated that NB and CNT could synergistically catalyze the electrochemically oxidation of NADH (β-nicotinamide adenine dinucleotide, reduced form) and NB-CNT exhibited a high performance with lowing the overpotential of more than 560 mV. The NB-CNT/GC electrode could effectively sense the concentration of NADH, which was produced during the process of oxidation of substrate (e.g. ethanol) catalyzed by dehydrogenase (e.g. alcohol dehydrogenase). The presented method for functionalization of CNT had several advantages, such as rapid and facile CNT functionalization, easy electrode fabrication and high electrocatalytic activity, etc., and could be used for fabrication electrochemical biosensor on the basis of dehydrogenase. __________ Translated from Acta Chimica Sinica, 2007, 65(1): 1–9 [译自: 化学学报]     

Polymer Nanocomposites Using Urchin‐Shaped Carbon Nanotube‐Silica Hybrids as Reinforcing Fillers

Summary: Carbon nanotubes (CNTs) have been grown on MCM‐41 supported Fe nanoparticles and the as‐prepared (no further purification) CNT‐silica hybrid was directly incorporated into nylon‐6 (PA6) by simple melt‐compounding. The urchin‐shaped CNT‐silica hybrid filler was observed to be homogeneously dispersed throughout the matrix by scanning electron and transmission electron microscopy. Compared with neat PA6, the tensile modulus and strength of the composite are greatly improved by about 110%, with incorporation of only 1 wt.‐% CNT‐silica filler.

SEM image and schematic representation showing polymer chains wrapping around the urchin‐shaped CNT‐silica hybrid filler.     

Small‐Sized Tungsten Nitride Particles Strongly Anchored on Carbon Nanotubes and their Use as Supports for Pt for Methanol Electro‐oxidation

The anchoring of small‐sized WN (tungsten nitride) nanoparticles (NPs) with good dispersion on carbon nanotubes (CNTs) offers an effective means of obtaining promising materials for use in electrocatalysis. Herein, an effective method based on grinding treatment followed by a nitridation process is proposed to realize this goal. In the synthesis, a solution containing H₄[SiO₄(W₃O₉)₄] (SiW₁₂) and CNTs modified with polyethylenimine (PEI‐CNTs) was ground to dryness. Small‐sized WN NPs were anchored onto the CNTs with good dispersion after calcination under NH₃. Under hydrothermal assembly conditions (absence of grinding), WN particles of larger size and with inferior dispersion were obtained, demonstrating the important role of the grinding process. The benefit of the small‐sized WN has been demonstrated by using WN/CNTs as a support for Pt to catalyze the methanol electro‐oxidation reaction. The mass activity of Pt‐WN/CNTs‐G‐70 (where G denotes the grinding treatment, and 70 is the loading amount (%) of WN in the WN/CNTs) was evaluated as about 817 mA mg^?1_Pt, better that those of commercial Pt/C (340 mA mg^?1_Pt) and Pt/CNTs (162 mA mg^?1_Pt). The Pt‐WN/CNTs‐G also displayed good CO tolerance. In contrast, Pt‐WN/CNTs prepared without the grinding process displayed an activity of 344 mA mg^?1_Pt, verifying the key role of grinding treatment in the preparation of WN/CNTs with good co‐catalytic effect.     

Fracture Behavior of Covalently Re-Modified MWNT/Epoxy Nanocomposites

Summary: In this work, a surface re-modified multi-walled carbon nanotube (MWNT) was prepared by the chemical attachment of oligomeric unsaturated polyester on the MWNT surface. The re-modified MWNT was incorporated in two concentrations of 0.35 and 0.70 Wt.% into epoxy resin in order to investigate its effect on morphology and mechanical behavior of the MWNT/epoxy nanocomposite. The transmission electron microscopy showed that the re-modification of MWNT surface improves its dispersion state in the epoxy matrix. The tensile measurements for the nanocomposite having different amounts of surface re-modified/not-modified MWNT showed that the fracture mechanism changed from brittle to tough beyond a certain amount of surface re-modified MWNT. The scanning electron microscopy findings on the fracture surface morphology of the resulted nanocomposite substantiated the observed phenomena.