Effect of Addition of Multiwalled Carbon Nanotubes on the Piezoelectric Properties of Polypropylene Filaments.

The effect of addition of multiwalled carbon nanotubes (CNTs) on the piezoelectric properties of polypropylene (PP) monofilaments has been investigated. Various amounts of CNTs (0%, 0.01%, 0.1% and 1% weight ratios) were melt-blended with PP and the resulting nanocomposites were extruded in a continuous process with simultaneous on-line poling to produce monofilaments. Concurrent stretching at a draw ratio of 5:1 and polarisation at applied electric fields of 15 kV of PP/CNT filaments was observed to enhance the piezoelectric properties. The microstructure and crystallinity of the filaments was analysed using scanning electron microscopy (SEM), differential scanning calorimetric (DSC) and Fourier transform infrared spectroscopy (FTIR) techniques. Voltage generation by the CNT-modified PP filaments was determined by the application of predetermined load impact. The results show that the incorporation of CNTs in the PP fibre structure has a considerable impact on the enhancement of piezoelectric properties of the PP filament obtained that the peak voltage generation was almost four fold (from 0.76 V to 2.92 V) when 0.1 wt% of CNTs added into the polymer. This is owing to the fact that carbon nanotubes act as nucleating agent for enhancing the crystallisation during the melt extrusion process.

Exclusive self-aligned ß-phase PVDF films with abnormal piezoelectric coefficient prepared via phase inversion.

Self-polarised poly(vinylidene fluoride), (PVDF), films were prepared via a facile phase-inversion technique wherein the polymorphism of the films was controlled from exclusive α- (>90%) to ß-phase (>98%) by simply varying the quenching temperature from 100 °C to -20 °C, respectively. At low temperatures, the ß-phase crystallites were found to be self-aligned, with the PVDF thin films possessing a high piezoelectric coefficient of up to -49.6 pm V(-1). The extraordinarily high ß-phase and piezoelectric coefficient of these PVDF films make them suitable for electroactive and energy harvesting applications.

Surface modification of titanium carbide with carbyne-containing nanocoatings.

The aim of this research is to investigate a novel approach to surface engineering of biomaterials that are based on transition metals of the groups IVA-VIA. The approach taken relies on the fact that, during the electropolishing of TiC surfaces, the removal of Ti atoms from the TiC surface surpasses that of C atoms. This leads to enrichment of the TiC surface with carbon. Transmission electron microscopic investigation showed that carbon-based films contain carbynes in the form of nanorod-like clusters with lengths in the range of 5-100 nm. This carbyne-containing layer is 50-100 nm thick. It was generalized that carbyne-containing nanofilms are formed on the carbide surface of transition metals of groups IVA-VIA during electropolishing. Since carbynes, being one-dimensional chain-like structures [(-C identical to C-)n/(=C=C=)n] with sp1 carbon-carbon hybridization, have the highest degree of biocompatibility because of their biological activity, the development of such surface bioengineering with carbynes extends applications of biomaterials based on transition metals of the groups IVA-VIA.

Microwave facilities for welding thermoplastic composites and preliminary results.

The wide range of applications of microwave technology in manufacturing industries has been well documented (NRC, 1994; Thuery, 1992). In this paper, a new way of joining fibre reinforced thermoplastic composites with or without primers is presented. The microwave facility used is also discussed. The effect of power input and cycle time on the heat affected zone (HAZ) is detailed together with the underlying principles of test piece material interactions with the electromagnetic field. The process of autogenous joining of 33% by weight of random glass fibre reinforced Nylon 66, polystyrene (PS) and low density polyethylene (LDPE) as well as 23.3% by weight of carbon fibre reinforced PS thermoplastic composites is discussed together with developments using filler materials, or primers in the heterogenous joining mode. The weldability dependence on the dielectric loss tangent of these materials at elevated temperatures is also described.

Permittivity measurement of thermoplastic composites at elevated temperature.

The material properties of greatest importance in microwave processing of a dielectric are the complex relative permittivity epsilon = epsilon'-jepsilon", and the loss tangent, tan delta = epsilon"/epsilon'. This paper describes two convenient laboratory based methods to obtain epsilon', epsilon" and hence tan delta of fibre-reinforced thermoplastic (FRTP) composites. One method employs a microwave network analyzer in conjunction with a waveguide transmission technique, chosen because it provides the widest possible frequency range with high accuracy. The values of the dielectric constant and dielectric loss of glass fibre reinforced (33%) low density polyethylene, LDPE/GF (33%), polystyrene, PS/GF (33%), and Nylon 66/GF (33%), were obtained. Results are compared with those obtained by another method using a high-temperature dielectric probe.

Numerical modeling of the temperature distribution within a bonded paper web when undergoing microwave heating in a waveguide

In this paper, a numerical technique is used to study the temperature distribution within the heated bonded paper web placed in a waveguide. The parameters of the problem were selected so as to best locate the test sample that would generate the desired absorbed power. The method of false transient was utilized to accelerate the numerical convergence and the equations were discretized with central difference in both time and space. The resulting system of equations was solved using an Alternating Direction Implicit scheme. Good agreement was achieved between the numerical solutions and the experimental validations.

On the origin of the high capacitance of nitrogen-containing carbon nanotubes in acidic and alkaline electrolytes.

The synthesis of nitrogenated carbon nanotubes (N-CNTs) with up to 6.1 wt% N, via the use of pyridine as the nitrogen containing carbon precursor, can provide a facile route to significantly enhance the low intrinsic specific capacitance of carbon nanotubes. The nitrogen functionalities determine this, at least, five-fold increase of the specific capacitance.

Insights from a thermography-based method suggesting higher carotid inflammation in patients with diabetes mellitus and coronary artery disease.

AIM: Diabetes mellitus (DM) is an independent risk factor for stroke. In a DM population, carotid atheromatosis is a major cause of stroke. The role of carotid plaque inflammation remains conflicting. Microwave radiometry (MWR) is a new non-invasive method allowing in vivo measurement of the temperature of tissues, so reflecting inflammation. The aim of this prospective study was to evaluate the impact of DM on carotid artery inflammation in patients with documented coronary artery disease (CAD). METHODS: Consecutive patients (n=300) with significant CAD were evaluated by: (1) ultrasound study of both carotid arteries; and (2) the temperature difference (ΔT) along each carotid artery on MWR. ΔT ≥ 0.90 °C was considered high ΔT. Vessel- and patient-based analyses were performed to determine the impact of DM on morphological and functional characteristics of carotid arteries. RESULTS: Out of 300 patients, 113 (37.7%) had DM. Patients with DM had similar carotid plaque thickness compared with patients without DM in both vessel- and patient-based analyses. In contrast, patients with DM exhibited higher ΔT values in both vessel- and patient-based analyses. On multivariate logistic regression analysis, DM was an independent predictor of high ΔT both unilaterally and bilaterally (OR: 1.66, 95% CI: 1.06-2.58, P=0.03 and OR: 1.96, 95% CI: 1.01-3.81, P=0.05, respectively). CONCLUSION: In patients with CAD, DM was an independent predictor of local carotid plaque inflammatory activation. Whether or not the assessment of functional plaque characteristics by MWR can be an additional prognostic tool independent of structural factors now needs to be further investigated.

Cellular factors involved in transcription and Tax-mediated trans-activation directed by the TGACGT motifs in human T-cell leukemia virus type I promoter.

Human T-cell leukemia virus type I (HTLV-I) encodes a 40-kDa nuclear protein, Tax, which stimulates transcription from three 21-base pair (bp) repeats in its U3 region. Tax trans-activation is mediated via cellular factors that interact with the TGACGT motifs in the 21-bp repeats. Gel mobility shift assay and UV cross-linking analysis show that two proteins of 52 and 46 kDa in size bind the 21-bp repeat specifically. Base substitutions in the TGACGT motif which abolished Tax trans-activation abrogated factor binding whereas the repeats containing mutations that did not affect Tax trans-activation supported factor binding as the wild-type repeat. The 52- and 46-kDa factors are present in human T-cell lines Jurkat and MT4 (HTLV-I transformed) and in HeLa cells but are undetectable in a human placental cell line JEG-3, which gave a reduced level of trans-activation. JEG-3 extracts contain a distinct DNA binding activity that shows analogous sequence requirements as the 52- and 46-kDa proteins in interacting with the various 21-bp repeats. c-Jun and CREB (cAMP-responsive element binding factor) can stimulate transcription from HTLV-I long terminal repeats in JEG-3 cells. At least two copies of the 21-bp repeats are required for optimal trans-activation by c-Jun and CREB. Most single point mutations in the TGACGT motif that abolished Tax trans-activation, however, did not affect c-Jun- or CREB-directed transcriptional enhancement. These data indicate that many transcription factors including c-Jun and CREB exert stimulatory effects on HTLV-I transcription although they do not directly respond to Tax. The 52- and 46-kDa cellular proteins most likely are involved directly in Tax-mediated trans-activation, and they are tentatively named Tax activation factors I and II, respectively.