Hsin-Ming Wu

Synthesis of Mg-Cu-Ti based amorphous alloys by mechanical alloying technique

This study examined the behavior of amorphous Mg-Cu-Ti based alloys synthesized by mechanical alloying technique. The microstructural evolution during mechanical alloying of the mixed powders was investigated by both X-ray diffraction and scanning electron microscopy. The phase stabilities of the as-milled powders were analyzed by the differential scanning calorimetry. Differential thermal analysis on the 12-h milled ternary Mg-Cu-Ti powders reveals endothermic peaks in the Mg40Cu40Ti20 and Mg40Cu35Ti25 at around 550 K and no such a peak is observed in the another ternary compositions. For the ternary and quaternary Mg-Cu-Ti based alloys, several amorphous powders were found to exhibit a wide supercooled liquid region before crystallization. The temperature interval of the supercooled liquid region defined by the difference between Tg and Tx, i.e. Tx-Tg, is 54K for Mg40Cu40Ti20, 53K for Mg40Cu35Ti25, 51K for Mg40Cu35Ti23B2, 62 K for Mg40Cu35Ti21Sn4, and 74 K for Mg40Cu35Ti21Ni5. As the results demonstrated, the small addition of Sn and Ni significantly improved the glass forming ability of the Mg-Cu-Ti based amorphous alloys.

NOVEL STABLE HUMIDITY LAYERS PREPARED BY SURFACE GRAFT POLYMERIZATION OF ANIONIC MONOMERS MIXING WITH PHENOL-FORMALDEHYDE

In this study, humidity-sensitive polymer layer containing phenol-formaldehyde resin prepared by spinning coating on the comb-shape type electrode followed by UV-graft polymerization of soluble monomer was performed to improve the sensitivity. In this investigation, grafting of P-styrenesulfonic acid sodium salt (NaSS) treated with hexamethyldisilazan (HMDSZ) plasma and acrylic acid (AAc) followed by isopropanol (IPA) plasma were used as monomer for UV surface graft polymerization. Results show the first one adding different ratio of phenol-formaldehyde resin. This type of sensor has linear response with %RH, and high sensitivity (impedance from 106 to 103). The impedance of second type of sensor was linear response with %RH, impedance varies from 107 to 105.

Improvement of Thermoplastic Polyurethane Nonwoven Hydrophilicity by Atmospheric Pressure Plasma Treatment with He and N2 Mixed Gases

Thermoplastic polyurethane (TPU) nonwoven has good mechanical properties for use in biomaterial. However, its inherent hydrophobic nature restricts its application. In this study, atmospheric pressure plasma treatment with He and N2 gases was employed to TPU nonwoven material to improve the surface hydrophilicity while retaining the hydrophobicility on the back side of the material. The surface wettability was measured by water contact angle analysis, and the surface chemical composition was analyzed by X-ray photoelectron spectroscopy (XPS). The surface morphology was examined using scanning electron microscopy (SEM). The experimental results reveal that oxygen-containing groups such as C–O and O–C=O are generated on the plasma-treated TPU surface, leading to improved wettablility of the material.

TEMPERATURE SENSITIVITY OF COMPOSITE HYDROGEL PREPARED BY SURFACE GRAFT POLYMER OF NIPAAm AND BAMBOO CHARCOAL POWDER

This study aimed at fabricating a new type temperature sensor device by taking advantages of electrical conductivity of bamboo charcoal powder and temperature sensibility of NIPAAm hydrogel. The resistance of such a composite device will be affected by temperature. Bamboo charcoal powders were first subjected to oxygen plasma treatment. The treated bamboo charcoal powders were then UV graft polymerization with N-isopropylacrylamide (NIPAAm) monomer solution to be immobilized on the electrode which had previously been modified with plasma of tetramethyltin (TMT) and O2 gas mixture. Using simple environment test to measure resistance, the LCST of bamboo charcoal powders mixed with NIPAAm hydrogel was found to be 31°C. At ambient temperatures higher than LCST, the electrode resistance decreases. The surface morphology of composite hydrogel was observed by SEM.

Effect of composition and heat treatment on the phase formation of mechanically alloyed Cr-B and Mo-B powders

Blended elemental Cr-B and Mo-B powders in atomic ratio of 67:33, 50:50, and 20:80 were subjected to mechanical alloying up to 60 h and subsequent heat treatment to investigate effect of composition and heat treatment on the phase formation of Cr-B and Mo-B powders. It was studied by X-ray diffraction and differential thermal analysis. Mechanical alloying these powder mixtures for 60 h leads essentially to a amorphous structure except for the Mo20B80 powder, which creates a partially amorphous MoB4 structure. Annealing at lower temperatures relieves the strains cumulative in the milled powders and creates no new phase. The structures obtained after annealing the milled powders at higher temperature vary and depend on the overall composition of the powder mixtures. Annealing the milled Mo-B powders having greater Mo content ends up with a dissociation reaction at higher temperature.

USE QCM TO MEASURE SELF-ASSEMBLING MONOLAYER, PLASMA MODIFICATION, AND SURFACE GRAFT POLYMERIZATION

The aim of this study was to investigate the frequency shift of the gold film electrode of a quartz crystal microbalances (QCM) made by steps of applying self-assembling monolayer (SAM), plasma treatment, and UV-induced graft polymerization on the surface. Thiol group containing 11-mercaptoundecanoic acid (MUA) was employed for depositing SAM onto gold surfaces. Oxygen plasma treatment was then applied to the SAM to generate sufficient amounts of peroxides and hydroperoxides, which could further initiate UV-induced graft polymerization. Measurements of contact angle and oscillation frequency on the prepared QCM indicate that the SAM-modified gold film surface provides an effective method of making the surface hydrophilic and altering the frequency of QCM through the plasma treatment and graft copolymerization with an appropriate monomer.

Preparation of SiC/MoSi2 composites by mechanical alloying and its fracture properties

Ball milling was utilized to make composite powders from either elemental Mo, Si, C powders or compound MoSi2 and SiC powders. The milled powders were hot-pressed in a vacuum furnace to produce 10 to 30 vol.% SiC-reinforced MoSi2 composites. The influence of microstructure on the indentation fracture toughness of the fabricated SiC/MoSi2 composites was investigated. The SiC particles present in the consolidated compound composite are larger than those in the elemental composite while the pores observed in the former composite are fewer than in the latter. The overall values of fracture toughness measured on the compound composites are higher than those of elemental composites. The major reason for the greater toughness of compound composites is due to the larger SiC particles and fewer pores in these materials.

Plasma Surface Treatment and Grafting of Nano-Gold Surface for Immobilization of Chitosan

Combination of biomaterials with nanotechnology has been applied to the immobilization of chitosan on nano-gold particles by plasma and grafting treatments. In this study, gold (Au) nanoparticles were first synthesized by chemical reduction method using mix- ing solution of HAuCl4 4H2O and sodium citrate or NaBH4. The synthesized gold nanoparticles were then reacted with 11- mercaptoundecanoic acid (MUA) containing thiol group to modify the surface of gold nanoparticle. The MUA-modified Au nanoparti- cles were subjected to O2 plasma pretreatment before the UV light grafting polymerization with N-Isopropylacrylamide (NIPAAm) on the plasma-treated Au nanoparticles to form a thermosensitive polymer on the surface. The functional groups on the grafted Au nanopar- ticles surface were combined with glutaraldehyde to immobilize biological molecules of chitosan. The results show that preparation of nano-Au particles using NaBH4 solution as reductant is better than using the sodium citrate solution. The preferable reaction temperature for the preparation using NaBH4 solution to produce nano-Au particles is 100°C. From the TEM observation the prepared Au nanoparti- cle was spherical-like and about 10~20 nm in size. The zeta potential measurement on the immobilized Au nanoparticles proves that chi- tosan was indeed immobilized on the Au nanoparticles surface.

FABRICATION OF QCM TYPE SMOTHER DETECTION SENSOR BY PLASMA POLYMERIZING SnOx ORGANIC-LIKE FILMS AND SPIN COATING WITH POLY ETHYLENE GLYCOL

Quartz crystal microbalances (QCM) are transducers for chemical and biochemical sensing. The oscillation frequency of QCM is affected by the adsorbed mass on the surface. In this work, a new room temperature type gas sensor device fabricated by organically hybridized plasma deposition of tetramethyltin (TMT) and oxygen. Post treatment with poly ethylene glycol (PEG) was developed to detect the ambient environmental smother, and the responses of the fabricated sensor to smother detection were investigated. SnOxCy thin films on the sensor electrodes were obtained by plasma deposition from TMT and O2 gas mixtures at room temperature. A spin coating post treatment on the SnOxCy thin films turns into hydrophilic property. The response of the QCM sensor to the smother detection shows a frequency drop during the burning of candle and has good detection sensitivity with Δf equal to 2400 Hz. Repeated smother testing with the QCM type smother detection sensor also indicates the stability of the fabricated sensor.

A NOVEL METHOD TO EVALUATE PLASMA DEPOSITED SILICON OXIDE BARRIER FILMS BY WATER CONTACT ANGLE MEASUREMENT UNDER DC VOLTAGE APPLICATION (FOR CONFERENCE PUBLICATIONS FROM ACCS 2011)

In this study, organic silicon thin film was deposited on a comb type electrode substrate surface using hexamethyldisilazane (HMDSZ) plasma deposition technique to enhance voltage withstanding capability. The wettability, morphology and capability to withstand voltage were investigated by water contact angle (WCA) measurement, SEM observations, AFM and ampere meter analysis, respectively. The WCA of the substrate is 92.3° after the plasma deposition. As voltage is applied to the electrode, the WCA lowers to 76.4° and the resulting current flow is 0.078 mA. If the voltage is continually applied to the device, the organic silicon film on the substrate starts to peel off, accompanied with a sharp increase in current, which is an irreversible phenomenon. From the SEM and AFM analysis, the voltage withstanding capability of the device can be enhanced by prolonging the plasma processing time in order to obtain thicker thin film.