Advanced Materials Research Vol. 1119

Abstract: The prime objective of this study was to fabricate epoxy polymer composite modified with graphene nanoplatelets (GP) and montmorillonite nanoclay (MMT) binary filler materials. Different loading percentages of individual and binary nanofillers were incorporated into an epoxy matrix system to investigate the synergistic effect of nanofillers on composites properties. Dynamic mechanical analysis (DMA) and three point bend test were carried out to investigate the viscoelastic and flexural properties of neat epoxy and nanofillers reinforced nanocomposites. Incorporation of 3 wt. % of MMT and 0.1 wt. % of GP resulted in better flexure strength, modulus and storage modulus although there is no significance change in glass transition temperature (Tg).

Abstract: Graphene layers were deposited on the surface of NiTi shape memory alloy (SMA) to enhance the spherical indentation depth and the phase transformed volume through an extra nanoscale cooling. The graphene-deposited NiTi SMA showed deeper nanoindentation depths during the solid-state phase transition, especially at the rate dependent loading zone. Larger superelastic deformation confirmed that the nanoscale latent heat transfer through the deposited graphene layers allowed larger phase transformed volume in the bulk and, therefore, more stress relaxation and depth can be achieved. During the indentation loading, the temperature of the phase transformed zone in the stressed bulk increased by ~12-43°C as the loading rate increased from 4,500 μN/s to 30,000 μN/s. The layers of graphene enhanced the cooling process at different loading rates by decreasing the temperature up to ~3-10°C depending on the loading rate.

Abstract: Highly stable silver nanoparticles synthesized in single-step green method by mixing silver nitrate and aqueous extract of Almond (Prunus amygdalus). Experiments were conducted to influence the change in the silver nitrate concentration and time on the synthesis of silver nanoparticles at room temperature under dispersed sun light. The almond extract acted both as the reducing and stabilizing agent for the synthesis of silver nanoparticles. The change in the color of the reaction mixture was monitored using UV-Visible spectrometry whereas particles synthesized were characterized using Scanning Electron Microscopy, Dynamic Light Scattering and Fourier Transform Infrared Spectroscopy. The synthesized nanoparticles were almost spherical in shape with an average size about 20 nm and they exhibited bacteriostatic property against E. coli.

Abstract: The use of nanoparticles with carbon dioxide foams has been proposed for enhanced oil recovery due to their robust chemical stability in harsh environment. The experimental study was performed by using nanoparticles stabilized carbon dioxide foams to study their recovery of residual oil by varying the carbon dioxide flow rates on different core samples such as sandstone and limestone. Experimental setup was divided into two different kinds of experiments which are the injection of carbon dioxide foams and the injection of nanoparticles assisted carbon dioxide foams in both sandstone and limestone core samples. For the CO₂ foam injection, it was found that limestone has higher oil recovery than sandstone rock samples with 38.67% recovery and 36.36% recovery for sandstone. With the nanoparticles assisted injection, the crude oil recovery increased to 41.82% and 45.33% for sandstone and limestone respectively. Limestone showed the higher porosity reduction at the end of experiment compared to sandstone with the porosity of 7.56% on limestone and 12.49% on sandstone respectively. This is due to the nanoparticles strongly absorbed at the limestone surfaces containing calcite component.

Abstract: Transformer is one of the major component, which is the most important device in power system. Their lifetime depends upon liquid insulation that help transfer the heat out of its winding inside of transformer. Transformer oil uses mineral oil that is the most commonly used has very slow process on decomposition and non-biodegrade. This paper presents the investigation on breakdown voltage of two types of natural ester oils, including palm oil and soy bean based-on ZnO nanofluids. Nanofluids that use nanoparticles modified by use of surfactant that are suspended by process of sonication. Different fraction of nanoparticles were investigated from 0.1% - 0.5% by weight. The breakdown voltage were measured according to ASTM D877. The voltage breakdown strength increased significantly when nanoparticles were added in oils. The obtained results will enable transformer industry to develop liquid insulation dielectric for use in transformer in the future.

Abstract: Ultraviolet Substrate Conformal Imprint Lithography (SCIL) is an economic nanolithography technique of imprinting high-fidelity patterns over large areas. It is an improvement to conventional UV-Nanoimprint lithography (NIL) with high resolution, flexibility and conformal imprinting. However the aspect-ratio of SCIL is limited due to its patterning by capillary forces and the PDMS material has very low Young’s modulus (<2Mpa) hence, resulting in deformation of the feature sizes during the imprint process. In general the residual layer between the imprinted structures is etched away to obtain high aspect ratio. But in industrial applications an array of different 3D patterns are imprinted in a single step, thus, the residual layer of each structure depends on its volume and viscosity of the imprint material, thereby making the etching process impossible to increase the feature size and aspect-ratio of each microstructure individually. Hence in this paper a new SCIL stamp technique is demonstrated to implement an enhancement of aspect ratio. In this process, a flexible polymer material, Polydimethylsiloxane (PDMS) is used as the stamp material. The heights of the structure on the stamp are supported by a metal layer (higher Young’s modulus), which provides higher stiffness and rigidity to the stamp and thereby avoiding distortion of the patterns on the stamp. Also the metal layer acts as an UV blocking mask: hence while patterning on an UV curable imprint material, the residual edges of the microstructures, which are subjected to decrease the feature size, are removed in the development process of the uncured polymer areas. Thus, irrespective of the number and shape of the microstructures, an enhancement of aspect ratio is attained in a single step. Conventional imprinting of circular polymer arrays with dimensions 90μm / 70nm on their master template resulted in increased feature size up to 150 μm, while the height varied between 90-66nm and thereby decreasing the aspect ratio. Imprinting with the proposed SCIL technique resulted in 96 μm / 74nm dimension, thus around 60 μm of feature size improvement is achieved

Abstract: We report a hybrid hetero p-n junction between Zinc Oxide (ZnO) microspheres and p-GaN thin film or poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS). ZnO microspheres, which have high crystalline quality, were synthesized by ablating a ZnO sintered target with focused pulsed laser at high fluence. Recent investigation has demonstrated that ZnO microspheres had high optical property and laser actions in the WGM (whispering gallery mode) from the microshperes under pulsed laser irradiation. In this study, we fabricated a hybrid hetero p-n junction between ZnO microspheres and p-GaN or PEDOT:PSS, and both p-n junctions with p-GaN or PEDOT:PSS had a good rectifying characteristic. In the case of p-GaN, electroluminescence was observed under forward bias.

Abstract: Preparation of n-type β-FeSi₂/intrinsic Si/p-type Si heterojunctions was accomplished by facing-target direct-current sputtering (FTDCS) and measuring their current-voltage characteristic curves at low temperatures ranging from 300 K down to 50 K. A mechanism of carrier transport in the fabricated heterojunctions was investigated based on thermionic emission theory. According to this theory, the ideality factor was calculated from the slope of the linear part of the forward lnJ-V plot. The ideality factor was 1.12 at 300 K and increased to 1.99 at 225 K. The estimated ideality factor implied that a recombination process was the predominant mechanism of carrier transport. When the temperatures decreased below 225 K, the ideality factor was estimated to be higher than two and parameter A was estimated to be constant. The obtained results implied that the mechanism of carrier transport was governed by a trap-assisted multi-step tunneling process. At high forward bias voltage, the predominant mechanism of carrier transport was changed into a space charge limit current process.

Abstract: Sputtered metal oxides of Zr, Ti, and Zn were investigated on their resistive switching properties. All these three oxides exhibit electrode independence of the on-state currents, implying presence of non-uniform distribution of the conduction paths. The formation and rupture of those low-resistance filaments determine the reversible stable conductions and transition thresholds, which is related to the oxygen vacancy. The change in filament size explains the effect of current compliance and sweeping bias under various deposition temperatures and ambient. The decrease or increase of conduction currents is ascribed to the varying length and cross-section area of the filaments.

Abstract: Optimization of the moulding parameters on the carbon black/graphite/epoxy (CB/G/EP) composite for bipolar plate application using the Taguchi method was carrying out. Moulding parameters of the compression moulding process such as moulding temperature, moulding pressure and moulding time were measured. Analysis of variance (ANOVA) shows that, the most significant moulding parameter is moulding time with percentage contribution of 59.98%.The confirmation experiment using additive model shows that, the electrical conductivity of CB/G/EP composites was 168.50 S/cm. The electrical conductivity of CB/G/EP composite was improved 65.72 % compare with the initial trial. The results show that Taguchi method is an effective approach to obtain the optimal moulding parameters of the CB/G/EP composites.