Comparative analyses of the electrical properties and dispersion level of VGCNF and MWCNT: Epoxy composites

The electrical properties and dispersion of vapor‐grown carbon nanofibers (VGCNF) and multiwalled carbon nanotubes (MWCNT)—epoxy resin composites are studied and compared. A blender was used to disperse the nanofillers within the matrix, producing samples with concentrations of 0.1, 0.5, and 1.0 wt % for both nanofillers, besides the neat sample. The dispersion of the nanofillers was qualitatively analyzed using scanning electron microscopy, transmission optical microscopy, and grayscale analysis. The electrical conductivity and the dielectric constant were evaluated. The percolation threshold of MWCNT epoxy composites is lower than 0.1 wt % while for VGCNF lies between 0.1 and 0.5 wt %. The difference on the dispersion ability of the two nanofillers is due to their intrinsic characteristics. Celzard's theory is suitable to calculate the percolation threshold bounds for the VGCNF composites but not for the MWCNT composites, indicating that intrinsic characteristics of the nanofillers beyond the aspect ratio are determinant for the MWCNT composites electrical conductivity. © 2012 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012     

Electro-optical and dielectric study of multi-walled carbon nanotube doped polymer dispersed liquid crystal films

The self-organising property of nematic liquid crystals (LCs) was used to align multi-walled carbon nanotubes (MWCNT) dispersed in them. MWCNT not only well integrate in the matrix but also, even at very low concentration, have a detectable effect on the LC properties that can be very attractive for display applications. In the present work, MWCNT were doped (0–0.5% wt/wt) in two different types of LCs. These MWCNT doped polymer dispersed LC (CPDLC) films were studied comprehensively using fundamental techniques. Polarising optical microscope (POM) and scanning electron microscope (SEM) techniques used for morphological study reveal that the LC droplet size remains unchanged with increase in MWCNT concentration. The electro-optical (EO) study performed by increasing voltage in steps of 10 V up to 100 V at an optimised frequency of 200 Hz and at temperature 25°C shows that the low MWCNT concentration films show good optical response than the higher one. The dielectric behaviour of CPDLC films in the frequency range 20 Hz to 20 MHz was investigated using precision impedance analyser. The obtained data were modelled with Debye and Cole-Cole methods to calculate relaxation time and distribution parameter (α). The zero value of α indicates Debye type relaxation processes.     

Effect of reaction parameters on the growth of MWCNTs using mesoporous Sb/MCM-41 by chemical vapour deposition

Mesoporous Si-MCM-41 molecular sieve was synthesized hydrothermally and different wt.% of Sb (1.0, 2.0, 3.0, 5.0, 10.0, 15.0 and 20.0) was loaded on it by wet impregnation method. The Sb/MCM-41 materials were characterized by various physico-chemical techniques such as XRD, TGA and TEM. The TEM image showed a honeycomb structure of the host material. They were used as catalytic templates for the growth of MWCNTs by CVD method with different temperatures at 700, 800, 900 and 1000 °C using acetylene as a carbon precursor. The reaction temperature was optimized for the better formation of MWCNTs and they were purified and then characterized by XRD, SEM, HR-TEM and Raman spectroscopy techniques. The formation of MWCNTs with diameter in the range of 4−6 nm was observed from HR-TEM. The good thermal stability and high productivity of catalyst observed in this study revealed that the 2 wt.% Sb loaded MCM-41 could be a promising support for the catalytic synthesis of MWCNTs at 800 °C by CVD method.     

Nanotubes as polymer composite reinforcing additive materials – A comparative study

Nitrogen-doped bamboo-shaped carbon nanotubes (N-BCNTs) and their non-doped conventional counterparts, multiwalled carbon nanotubes (MWCNTs) were compared as polymer reinforcing additives in polyvinyl chloride (PVC) matrix. The nanotubes were synthetized by catalytic chemical vapor deposition (CCVD) method. The purity of both nanotubes was measured by thermogravimetric analysis (TGA) and found to be >91%. Further analysis on the morphology and size of the carbon nanotubes (CNTs) were performed by transmission electron microscopy (TEM). The PVC powder was impregnated with CNTs in ethanol by using tip ultrasonicator. The dispersion media was evaporated, and the CNT/PVC powder was used to produce polymer fibers. The orientation of carbon nanotubes in the PVC matrix was characterized by scanning electron microscopy (SEM), and the presence of nanotubes were confirmed in case of all PVC samples. It can be observed on the SEM images that the nanotubes are fully covered with PVC. The tensile strength of the nanotube containing samples was tested and the N-BCNT/PVC composite was found to be better in this sense, thanks to the extraordinary structure of the nanotube. In case of the N-BCNT/PVC composite the measured young modulus was 39.7% higher, while the elongation at brake decreased by 33.6% compare to the MWCNT/PVC composite. These significant differences in the mechanical properties of the composites can be explained with the stronger interaction between N-BCNTs and PVC.     

Application of Raman spectroscopy to study of the polymer foams modified in the volume and on the surface by carbon nanotubes

Polylactide nanocomposites with multi-walled carbon nanotubes (PLA/MWCNT) in the form of porous foams made of a biocompatible, biodegradable and environmentally friendly polymer with a small amount of carbon nanotubes, were investigated in this work. Additionally, PLA/MWCNT porous nanocomposites were coated with MWCNTs using the electrophoretic deposition method (EPD). All samples were characterized by a porosity of about 90%, showing pore sizes in the range of 100 to 200 μm, for PLA/MWCNT foam, however, EPD deposition resulted in an decrease in the number of smaller pores in PLA/MWCNT + MWCNT (EPD) foam. The porous polymer (PLA) matrix, shows almost twofold increase in crystallinity while depth penetrating the volume of the sample. The crystallinity, of the PLA/MWCNT foam, at first is growing then it gradually lowers, while for the PLA/MWCNT + MWCNT(EPD) foam almost does not change. This behavior points toward significant distinction between surface and interior of the samples. A detailed analysis of Raman spectra indicates related carbon structures occurring in the nanomaterial foams: graphene and graphite phases, CNT and also carbon amorphous phases. The characteristics of a single-shell vibration are visible by the character of the G-band. The estimated crystallite size in PLA/MWCNT + MWCNT(EPD) is about 3 times smaller than that in the PLA/MWCNT.     

Investigation of hydrogen storage in MWCNT–TiO2 composite

The hydrogen storage capacity of MWCNT–TiO₂ composite has been evaluated in the present work. The composite has been prepared by means of ultrasonication followed by drop casting on substrates. Morphology, structural and functional group studies of the prepared samples are carried out by transmission electron microscopy (TEM), scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy. Then, the samples are hydrogenated in the hydrogenation chamber as a function of time. Hydrogen storage capacity of the composite sample is found to be 0.9 wt% at 100 °C. Hydrogen uptake of the composite is accounted for the spillover mechanism in CNTs–metal oxide composite. Desorption temperature range, activation energy of desorption, binding energy of hydrogen are determined from thermogravimetric (TG) analysis.     

A comparative study on the AC/DC conductivity,dielectric and optical properties of polystyrene/graphene nanoplatelets (PS/GNP) and multi-walled carbon nanotube (PS/MWCNT) nanocomposites

Polystyrene/graphene nanoplatelets (PS/GNP) and polystyrene/multi-walled carbon nanotube (PS/MWCNT) nanocomposites were prepared through solution mixing processing. The effect of carbon filler (CF) (GNP or MWCNT) doping on the DC/AC electrical conductivity, dielectric characteristics and optical parameters (absorption coefficient, α and band gap energy, E_g) of nanocomposites were investigated and compared for similar doping concentrations. The observed behavior of the DC surface conductivity for PS/CF nanocomposites was explained according to the classical percolation theory, where the percolation thresholds (ϕ_c) for PS/GNP and PS/MWCNT nanocomposites were determined as 12.0 vol% and 3.81 vol% and the critical exponents (t) were calculated as 2.19 and 2.13, respectively. These results indicate that CFs create three dimensional CF network in PS matrix. The dielectric relaxation properties and the AC conductivity studied by means of Broadband Dielectric Spectroscopy (BDS) measurements, showed that the presence of carbon fillers significantly enhanced the capacitive/charge storage capabilities of the nanocomposites. The optical band gap energies (E_g) of PS/GNP and PS/MWCNT nanocomposites were obtained by using Tauc method. From applicative point of view, with their enhanced dielectric and AC conductivity properties of the PS/GNP and PS/MWCNT nanocomposites have the potential to be used in energy storage and electromagnetic interference (EMI) shielding applications.     

A comprehensive study on the impact of RGO/MWCNT hybrid filler reinforced polychloroprene rubber multifunctional nanocomposites

Flexible dielectric chloroprene rubber (CR) nanocomposites reinforced by one-dimensional carbon nanotube (CNT)/two dimensional reduced graphene oxide hybrids have been prepared using two-roll mill mixing technique. Non-covalent π-π interaction between multiwalled carbon nanotubes (MWCNTs) and reduced graphene oxide (RGO) nanosheets and the secondary interaction between fillers and chloroprene rubber matrix are responsible for generating the effective load transfer between RGO/MWCNTs and CR. The prepared RGO-MWCNT hybrid nanocomposites with high dielectric constant (≈650), low dielectric loss (≈0.42) and high energy storage efficiency (78.6%) values are practically good enough to use as a low cost polymeric dielectric layer in transistors. Furthermore, the prepared nanocomposites showed excellent electromagnetic effectiveness; a maximum shielding efficiency of 11.87 dB @ 3.5 GHz was achieved at 4 phr of MWCNT loading. This excellent electromechanical performance can be ascribed to the synergistic effect of RGO-MWCNT hybrid suggesting that this novel hybrid nanocomposite serves as an attractive candidate in modern electronics and electric power systems.     

Attachment of Nanoparticles to Pyrolytic Graphite Electrode and Its Application for the Direct Electrochemistry and Electrocatalytic Behavior of Catalase

Abstract

A highly hydrophilic, nontoxic, and conductive effect of colloidal gold nanoparticles (GNP) and multi-walled carbon nanotubes (MWCNT) on pyrolytic graphite electrode has been demonstrated. The direct electron transfer of catalase (CAT) was achieved based on the immobilization of MWCNT/CAT-GNP on a pyrolytic graphite electrode by a Nafion film. The immobilized catalase displayed a pair of well-defined and nearly reversible redox peaks in 0.1 M phosphate buffer solution (PBS) (pH 6.98). The dependence of E°′on solution pH indicated that the direct electron transfer reaction of catalase was a single-electron-transfer coupled with single-proton-transfer reaction process. The immobilized catalase maintained its biological activity, showing a surface controlled electrode process with an apparent heterogeneous electron transfer rate constant (k _s) of 1.387±0.1 s^?1 and charge-transfer coefficient (α) of 0.49, and displayed electrocatalytic activity in the electrocatalytic reduction of hydrogen peroxide. Therefore, the resulting modified electrode can be used as a biosensor for detecting hydrogen peroxide.