The importance of controlling microchannel surface wetting by a continuous-phase liquid on stable preparation of oil-in-water (O/W) emulsion was assessed using a flow-focusing stainless steel microreactor. n-Dodecane and 1% sodium dodecyl sulfate (SDS) solution were used respectively as the dispersed phase and continuous phase. The stainless steel microchannel surfaces were modified by mirror and matte finishing, with and without silicon (Si) ion plating. In contrast to mirror finishing, Si plating and matte finishing were more effective for lowering the contact angle of water under ambient air. The combined matte finished/ Si plated surface exhibited the lowest contact angle of water, and therefore the highest contact angle of dodecane in water. For mirror-finished microchannels, O/W emulsion was prepared at the beginning of the run, whereas droplet formation ceased within 30 min, probably because of microchannel surface wetting by dodecane. A more stable preparation of O/W emulsion was achieved for at least 5 h when combined matte finished/ Si plated microchannels were used. Results show that a stable preparation of O/W emulsion depended on complete wetting of microchannels by the continuous-phase liquid and on the low affinity of microchannels for the dispersed-phase liquid in water.

View full abstract

Fiber reinforced plastic (FRP), carbon fiber reinforced plastic (CFRP), and polycarbonate (PC) are three components being applied widely and increasingly in automobile and aerospace industries because of their wide range of beneficial physical properties. This study investigated microfabrication of laser cutting of three samples (FRP, CFRP, and PC) using a Ti:sapphire femtosecond laser (90 fs pulse width, 800 nm wavelength, 1 kHz frequency). Experimental results were analyzed using optical microscopy and scanning electron microscopy. Results show that edge angles of upper and lower cross-sections on the three samples were cut precisely to nearly 90 deg angles. The cutting results of FRP and CFRP demonstrated that the fiber damage is slight and that a smooth surface was obtained. However, the crosssection of PC cutted was not burnt with partial damage. For comparison, laser cutting using CO₂ laser was also performed on the three samples. Experimental results showed that microfabrication using femtosecond laser is far superior because it creates a smoother surface than the CO₂ laser, with little or no thermal damage. In conclusion, microfabrication by cutting these three materials (FRP, CFRP, and PC) was possible using a femtosecond laser.

View full abstract

Raman spectroscopy is widely used to analyze the crystallographic states of materials surfaces and thin films. Raman shift is informative to analyze stresses or defective bonds on surfaces. However, because of the instability of room temperature, the overall precision of the measured Raman shift is not always satisfied in a commercial Raman spectroscopy system. In this report, we describe how room temperature affects the Raman shift in a spectrometer with large dispersion. The temperature dependence of the system was predicted theoretically by a difference in thermal expansion coefficients between an optical bench and diffraction grating, which indicates that a linear shift of wavenumber is effective to cancel the apparent temperature shift. As an example of high-resolution measurements, strain-induced Raman shift of diamond was calibrated by the reference emission line of Hg to detect a shift of less than the resolution: 0.3 cm^－1. Furthermore, laser-induced heating of Si surface was evaluated only by calibration based on room temperature without using any reference emission lines.

View full abstract

A 1-octadecanethiol self-assembly monolayer（ODT-SAM）was formed on electroless Au/Ni-P layers to improve corrosion resistance. However, ethanolic solutions are inferior to aqueous solution in terms of safety and cost. For this study, ODT-SAMs were obtained from aqueous solutions. A nonionic surfactant was used to dissolve ODT in water. The adsorption of ODT was evaluated based on the contact angle of water. The corrosion resistance was evaluated using the salt spray test. The corrosion resistance of ODT-SAMs obtained by immersion for 300 s in an aqueous micellar solution of the surfactant concentration of at least 2.3 × 10^－1 mol/L and the ODT concentration of 5.0 × 10^－3 mol/L was equival ent to that of ODT-SAMs from ethanolic solutions. The formation status of the ODT-SAMs was examined using infrared reflection absorption spectroscopy. The structure of ODT-SAMs on a gold plated surface in an aqueous micellar solution was compared to that of ODT-SAMs on a gold plated surface in an ethanol solution, revealing no difference. No deterioration in bondability was observed when the solder-ball bondability and wire bondability of an Au/Ni-P substrate on which ODT-SAMs obtained from an aqueous micellar solution were formed. Results show that ODT-SAMs obtained from aqueous micellar solutions are useful as corrosion inhibitors for electroless Au/Ni-P layers used in printed wiring boards.

View full abstract