Advanced Materials Research Vols. 93-94

Abstract: Preparation of nanoparticles by pulsed Nd:YAG (1064 nm) laser ablation on copper target submerged in distilled water has been studied. Effects of pulse power and liquid height were investigated. Colloidal nanoparticles were characterized by UV-Vis spectroscopy, Raman dynamic light scattering and transmission electron microscopy. The concentration of nanoparticles was increased with the pulse power at a particular liquid height or volume. The size of nanoparticles related complicatedly to both parameters. The optimum conditions were the pulse power of 80 W and the liquid height of 3-4 mm. The obtained mean particle size was 20-37 nm, having the maximum UV-Vis absorption wavelength at 617-630 nm. The colloids contained mainly copper oxide nanoparticles.

Abstract: A comparative study of TiO2 films on glass substrates produced by sol- gel dip coating technique using two types of titania precursors were performed. The two types of titania solutions with and without triton x-100, poly (ethylene glycol) were used to prepare the films. The dip coated films were dried at 55°C and calcined at 400 - 600°C for 4 hrs resulting in smooth and transparent TiO2 films. Morphology and phases of the films were investigated using SEM and XRD, respectively. Anatase phase was found to be dominant in all samples with various degree of crystallinity depending on the calcination temperatures and whether the templating agents were used. The templating agent was found to effectively inhibit the crystallization and growth of the crystallites of the films. Morphology of the TiO2 particles was found to be in the nanoscale level. All films fabricated were found to effectively degrade cyanide even though no obvious relations between processing method including calcinations temperature and the use of template were found.

Abstract: This work focused on an improvement of flame retardant properties of acrylonitrile-butadiene-styrene (ABS) by varying amount of silica and organomontmorillonite (OMT). The silica was extracted from agricultural waste such as rice husk by chemical treatment. The obtained silica was characterized by SEM-EDX, XRF, FTIR, laser particle size analysis, and surface area analysis. After that, the rice husk silica (RHS) was surface-modified with 3-aminopropyltrimethoxysilane (AMMO) before blending with ABS and OMT at various ratios by melt blending technique using twin-screw extruder. The effect of silane coupling agent on flammability properties of ABS nanocomposites was studied. The prepared nanocomposites were characterized by TEM to examine the dispersibility of OMT and AMMO-g-RHS in ABS matrix. The flammability properties were evaluated by measuring the limiting oxygen index (LOI) values and UL-94 classes. The TEM results revealed that the ABS/OMT/AMMO-g-RHS nanocomposites were a kind of exfoliated structure. The modified silica particles and OMT were found to disperse and reside in the SAN phase of the matrix. Furthermore, OMT and modified silica could enhance flame retardant properties of ABS polymer matrix because of a synergistic effect between OMT and modified silica during the combustion of ABS nanocomposites.

Abstract: Alumina nano-particles was grafted with poly(2-hydroxyethyl methacrylate) (PHEMA) utilizing the sequential method; that is, the alumina surface was first rendered with initiator, benzophenone, by UV-irradiation followed by the grafting polymerization of HEMA on the surface which was initiated thermally and propagated via the free-radical polymerization. FT-IR spectroscopy confirmed the successful grafting of PHEMA onto the alumina surface. Determined by thermalgravimetry (TG), the amount of benzophenone on the alumina surface was found to increase with the UV-irradiation time; however upon grafting of PHEMA, the amount of grafted-PHEMA was the same irrespective of the reaction time. The glass transition temperature (Tg) of grafted-PHEMA on alumina particles was approximately 93 °C that is higher than that of PHEMA which has Tg around 85 °C. This indicates the more restricted movement of grafted-PHEMA compared with the ungrafted-PHEMA.

Abstract: The use of titanium for medical and dental applications is on the rise because of their excellent biocompatibility. However, some properties of pure titanium are not sufficient. Alloying with copper can improve mechanical properties needed for dental use. A recent research on Ti-Cu cast alloy indicated that ductility decreased with increasing copper concentration, but addition of copper improved grindability and wear resistance, with lower corrosion resistance. The objective of this research is to study sintering of Ti-Cu alloys; their microstructure and hardness, and the effect of copper content to their sintered density. Ti-Cu alloys were produced via powder metallurgy. Titanium powder was mixed with copper powder with chemical composition of 2, 4, 7 and 10 wt%. Lubricant was added in alloy powder with 0.5% of total weight, followed by cold compaction under 254 MPa pressure. Debinding and sintering was carried out at 400oC for 0.5 hr and 1000oC for 1 hr respectively in argon atmosphere. Condition with highest density was found in 10wt%Cu composition; having highest hardness of 317 Hv. Differential thermal analysis of Ti-15Cu under N2 atmosphere showed exothermic reaction at 1078oC. Phase formation of the sintered alloys followed the Ti-Cu equilibrium phase diagram.

Abstract: In this study, we demonstrate the disposable polydimethylsiloxane (PDMS) microchip provided for DNA amplification. The device consists of two main parts. The first part is PDMS/glass stationary chamber, the other part is a temperature-control microdevice on SiO2/Si substrate. This device consists of a thin film Pt-microheater and a Pt-temperature sensor, which were fabricated with CMOS compatible process. The performance of the device in the DNA amplification shows that, with 10 μl of PCR mixture volume, the approximately 700 bp DNA were successfully amplified within 50 minutes by 30 PCR cycles. The amplified products were comparable with those of a conventional method using electrophoresis. The PCR chip is also suitable for mass production.

Abstract: In this work a micro flow sensor, using a double gate Ion Sensitive Field Effect Transistor (ISFET) and two metal electrodes, for fluid flow rate measurement in micro-channels were fabricated and demonstrated. By the channel fabrication the molds were patterned reversely on a silicon wafer using Deep Reactive Ion Etcher (DRIE). The double gate ISFET and two metal electrodes were placed on the mold in the distance 15 millimeters. The channels were formed using polydimethylsiloxane (PDMS) from the mold with the width 1000 and 2000 micrometer and the depth of 250 micrometer. After removing PDMS from the mold the channel was bonded with glass substrate by RF plasma technique. By the verification of flow sensors working range water and one mole of sodium nitrate solution were alternated in flow channel. The fluid flow rate were compared with the flow rate from weighing. It found from the comparison that the high deviation was found at low flow rate. Furthermore, the deviation depends also on the dimension of the flow channel.

Abstract: Ultra-thin Al films were deposited with different deposition times on silicon wafer and copper grid by dc magnetron sputtering. The sputtering power of 200 watt and Ar flow rate of 20 sccm were used to prepare the films. The deposition times were 40, 120 and 240 second, respectively. The deposited Al films were, then, left in the air under the humidity of 60% for 20 days. The crystal structure of ultra-thin Al films deposited on silicon wafer and copper grid were investigated by glazing x-ray diffraction (GXRD) and transmission electron microscopy (TEM), respectively. The XRD results show that after the ultra thin Al films were exposed to the air, the Al was oxidized and the Al2O3 was formed at room temperature. In addition, Al deposited for 120 and 240 second can form polycrystalline of -Al2O3 with preferred orientations of (110) and (311) planes. The TEM images show that the particle size of -Al2O3 was about 8.5 nm for deposited time of 120 second. Moreover, the spectroscopic ellipsometry (SE) data and simulation model of Bruggemann effective medium approximation (BEMA) was used to determine the volume fraction of Al2O3.

Abstract: The synthesis of cellulosic plastic films from waste cotton fabrics under homogeneous conditions by microwave heating using lauroyl chloride as an esterifying agent was studied. Nevertheless, the cellulose laurate film obtained was quite brittle than some other commercial synthetic polymers. Thus, the aim of this work was to investigate the effects of plasticizer on the properties of cellulose laurate film. Cellulose laurate was plasticized with each plasticizer, triethyl citrate (TEC), dibutyl phthalate (DBP), and epoxidized soy bean oil (ESO) at different amounts. The content of plasticizer was varied from 3% to 9% w/w of dry cellulose laurate. The effects of plasticizer (i.e., type and content) on mechanical properties of plasticized cellulose laurate films were investigated. The morphology and structure of cellulose laurate were confirmed by SEM, FTIR, and 1H-NMR analysis, whereas the thermal properties were characterized by TGA.

Abstract: In this work, we developed a 3-dimensional bone tissue engineering scaffold from type B gelatin and hydroxyapatite. Two types of scaffolds, pure gelatin (pI~5) (Gel) and gelatin/hydroxyapatite (30/70 wt./wt.) (Gel/HA), were prepared from concentrated solutions (5% wt./wt.) using foaming/freeze drying method. The results SEM revealed the interconnected-homogeneous pores of Gel and Gel/HA were 121  119 and 148  83m, respectively. Hydroxyapatite improved mechanical property of the gelatin scaffolds, especially at dry state. Compressive modulus of Gel and Gel/HA scaffolds were at 118±21.68 and 510±109.08 kPa, respectively. The results on in vitro cells culture showed that Gel/HA scaffolds promoted attachment of rat’s mesenchymal stem cells (MSC) to a 1.23 folds higher than the Gel scaffolds. Population doubling time (PDT) of MSC on Gel and Gel/HA scaffolds were 51.16 and 54.89 hours, respectively. In term of osteogenic differentiation, Gel/HA scaffolds tended to enhance ALP activity and calcium content of MSC better than those of the Gel scaffold. Therefore the Gel/HA scaffolds had a potential to be applied in bone tissue engineering.