Microwave exfoliated reduced graphene oxide epoxy nanocomposites for high performance applications

Graphene has captured the attention of scientific community due to recently emerging high performance applications. Hence, studying its reinforcing effects on epoxy resin is a significant step. In this study, microwave exfoliated reduced graphene oxide (MERGO) was prepared from natural graphite for subsequent fabrication of epoxy nanocomposites using triethylenetetramine (TETA) as a curing agent via in-situ polymerization. Thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), C¹³ NMR spectroscopy, X-ray photoelectron spectroscopy (XPS) and ultraviolet–visible (UV–vis) spectroscopy were employed to confirm the simultaneous reduction and exfoliation of graphene oxide. The reinforcing effect of MERGO on epoxy resin was explored by investigating its static mechanical properties and dynamic mechanical analysis (DMA) at MERGO loadings of 0 to 0.5 phr. The micro-structure of epoxy/MERGO nanocomposites was investigated using scanning electron microscope (SEM), transmission electron microscope (TEM) and XRD techniques. The present work reports an enhancement of 32%, 103% and 85% in tensile, impact and flexural strength respectively of epoxy by the addition of even 0.25 phr MERGO. At this loading elastic and flexural moduli also increased by 10% and 65%, respectively. Single-edge-notch three-point-Bending (SEN-TPB) fracture toughness (K_IC) measurements were carried out where a 63% increase was observed by the introduction of 0.25 phr MERGO. The interfacial interactions brought about by graphene also benefited the dynamic mechanical properties to a large extent in the form of a significant enhancement in storage modulus and slightly improved glass transition temperature. Considerable improvements were also detected in dielectric properties. The epoxy nanocomposite also attained an ac conductivity of 10⁻⁵ S/m and a remarkable increase in dielectric constant. The simple and cost effective way of graphene synthesis for the fabrication of epoxy/MERGO nanocomposites may be extended to the preparation of other MERGO based polymer nanocomposites. This remarkable class of materials has thrown open enormous opportunities for developing conductive adhesives and in microelectronics.     

Investigation on the panchromaticity of silver-doped poly(vinyl alcohol)/acrylamide photopolymer

An investigation on the panchromaticity of a silver-doped poly(vinyl alcohol)/acrylamide photopolymer system is presented in this paper. Frequency-doubled Nd:YAG (532 nm) and Ar? (488 nm) lasers were used for the characterization of the films. Previous studies using an He-Ne laser (632.8 nm) showed that plane-wave transmission grating with a high diffraction efficiency of 75% could be stored in the optimized film. From the present study, it was noted that transmission gratings with 70% diffraction efficiency could be recorded using Ar? and Nd:YAG lasers, thereby elucidating the possibility of using the developed photopolymer system as a competent panchromatic recording medium.     

Molecular Weights of Reactive Systems Employing Anionic Polymerization

Anionic polymerization has been successfully employed for reactive processing, the most notable example being that of nylon RIM [1] using caprolactam polymerization. Here, fast polymerization is achieved with the help of a combination of a catalyst and an initiator under practically anhydrous conditions. This polymerization method leads to a narrow molecular weight distribution and a Poisson distribution of the individual chain lengths. Analytical expressions for calculating the number-average and weight-average degrees of polymerization of the polymer chains from the degree of conversion have been derived based on this knowledge [2]. But in a reactive system where a substantial amount of monomer may be present during most of the processing time, the average must include the monomer units present. Only such averages will be of use in correlations of molecular weight with viscosity and degree of conversion with viscosity, which are of importance in the design of a reactive processing system. A method to compute such average molecular weights is presented here.     

Electrical properties of In<Subscript>2</Subscript>Se<Subscript>3</Subscript> single crystals and photosensitivity of Al/In<Subscript>2</Subscript>Se<Subscript>3</Subscript> Schottky barriers

In₂Se₃ single crystals ∼40 mm long and 14 mm in diameter were grown by the Bridgman method. The composition of grown single crystals and their crystal structure were determined. The conductivity (σ) and Hall constant (R) of grown single crystals were measured and the first Schottky barriers Al/n-In₂Se₃ were fabricated. Rectification and photovoltaic effect were detected in the new structures. Based on the study of the photosensitivity spectra of Al/n-In₂Se₃ structures, the nature of the interband transitions and band gap of In₂Se₃ crystals were determined. It was concluded that the new structures can be applied to develop broadband photoconverters of optical radiation.     

Analysis of the pour point of coconut oil as a lubricant base stock using differential scanning calorimetry

One of the major disadvantages of vegetable oils as base stock for lubricants is their high pour points. In this paper the crystallisation behaviour of coconut oil and the effect of additive addition and the chemical modification on its pour point were analysed using differential scanning calorimetry (DSC). Coconut oil showed the highest pour point among the vegetable oils considered in the study. This can be attributed to the predominantly saturated nature of its fatty acid constituents. Addition of additives did not show any significant improvement in the pour point of coconut oil. The chemical modification procedures described in this work have been effective in improving the pour point of coconut oil to some extent. The DSC method used in the present work has been found to be helpful in understanding the crystallisation behaviour of vegetable oils with different fatty acid compositions, the effect of additive addition and the chemical modification on pour point of coconut oil. Copyright © 2008 John Wiley & Sons, Ltd.     

Predicting customer behavior in the market-space: a study of Rayport and Sviokla’s framework

The rapidly evolving phenomenon of the World Wide Web and the creation of a new international arena for electronic commerce have expanded the possibilities for the marketing of products and services. The role played by customer behavior in the market-space is still not entirely understood and calls for investigations into the significance of customer attitudes and loyalty. In this article, a model is developed; it examines the significance of content, context, and infrastructure in determining customer loyalty. An empirical study involving 145 subjects was conducted to test this model and to gain a better understanding of the relationship between customer belief about a Web site (specifically, an e-publishing site) and customer behavior (such as attitudes toward brand and customer loyalty).The results indicate that customer attitude is influenced by belief about brand equity (value), which is affected by the content, context, and infrastructure. Customer loyalty is determined by attitude and belief about the context in which the products or services are offered. These findings provide a better understanding of customer behavior associated with Web sites in the market-space, also confirm the proposition of Rayport and Sviokla that ‘customer loyalty is developed at the context level’.     

Synthesis and characterization of chiral main chain polyesters with polar segments tailored for second harmonic generation

The synthesis, characterization and solvatochromic behavior of a new series of chiral polyesters are reported. These polymers with -conjugated donor-acceptor segments were synthesized with a view to be suitable for second harmonic generation. The polyesters were prepared by the reaction of diacid chlorides with biphenolic azo chromophores with -conformation and optically active dihydroxy compound (isosorbide). The polymers containing isosorbide units are optically active. They showed T _g between 100°C to 160°C and are stable up to 400°C. A red shift in the longer wavelength absorption band of these polymers in UV-Vis. absorption spectra (positive solvatochromism) shows that the dipole moment of excited state is higher than that of the ground state. Therefore these polyesters are expected to have good second harmonic generation capability.     

Transparent p-AgCoO2/n-ZnO diode heterojunction fabricated by pulsed laser deposition

Transparent diode heterojunction on ITO coated glass substrates was fabricated using p-type AgCoO₂ and n-type ZnO films by pulsed laser deposition (PLD). The PLD of AgCoO₂ thin films was carried out using the pelletized sintered target of AgCoO₂ powder, which was synthesized in-house by the hydrothermal process. The band gap of these thin films was found to be ∼ 3.89 eV and they had transmission of ∼ 55% in the visible spectral region. Although Hall measurements could only indicate mixed carrier type conduction but thermoelectric power measurements of Seebeck coefficient confirmed the p-type conductivity of the grown AgCoO₂ films. The PLD grown ZnO films showed a band gap of ∼ 3.28 eV, an average optical transmission of ∼ 85% and n-type carrier density of ∼ 4.6 × 10¹⁹ cm^− 3. The junction between p-AgCoO₂ and n-ZnO was found to be rectifying. The ratio of forward current to the reverse current was about 7 at 1.5 V. The diode ideality factor was much greater than 2.     

Effect of Filler Content on the Dielectric Properties of PTFE/ZnAl2O4–TiO2 Composites

ZnAl₂O₄–TiO₂ (ZAT)/polytetrafluoroethylene (PTFE) composites were prepared by powder processing method. The structure and microstructure of the composites were analyzed using X-ray diffraction and scanning electron microscopic techniques. The effect of different volume fraction of ZAT (0–0.6) on the dielectric properties of the composites was investigated at 1 MHz and at the microwave frequency of 7 GHz. The dielectric properties (relative permittivity and dielectric loss) were found to increase with the ZAT content. The samples with 60 vol.% of ZAT filler showed a relative permittivity of 3.9 and dielectric loss of 0.009, respectively, at 7 GHz. The variation of relative permittivity and dielectric loss showed only a very small variation with temperature in the range 25°–70°C for various ZAT/PTFE composites. The relative permittivity obtained experimentally were compared with that of the theoretical values predicted using modified Lichtenecker, Jayasundere—Smith, and Series mixing formulae. They were found to agree well with the predicted values for low filler content.