Fabrication of a micro-direct methanol fuel cell using microfluidics

A direct-methanol fuel cell containing three parts: microchannels, electrodes, and a proton exchange membrane (PEM), was investigated. Nafion resin (NR) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PS) were used as PEMs. Preparation of PEMs, including compositing with other polymers and their solubility, was performed and their proton conductivity was measured by a four point probe. The results showed that the 5 % Nafion resin has lower conductivity than the 5 % PS solution. The micro-fuel cell contained two acrylic channels, PEM, and two platinum catalyst electrodes on a silicon wafer. The assembled micro-fuel cells used 2 M methanol at the flow rate of 1.5 mL min^?1 in the anode channel and 5 × 10^?3 M KMnO₄ at the flow rate of 1.5 mL min^?1 in the cathode channel. The micro-fuel cell with the electrode distance of 300 ??m provided the power density of 59.16 ??W cm^?2 and the current density of 125.60 ??A cm^?2 at 0.47 V.     

RESS for the preparation of fluorinated porphyrin nanoparticles

Rapid Expansion of Supercritical Solutions (RESS) was used to produce clean, surfactant-free nanoparticles (average size = 60 nm) of a fluorinated tetraphenylporphyrin from supercritical solutions with CO2.     

The formation of fluorinated tetraphenylporphyrin nanoparticles via rapid expansion processes: RESS vs RESOLV

Organic nanoparticles of a fluorinated tetraphenylporphyrin (TBTPP) were produced by rapid expansion of supercritical CO(2) solutions into both air (RESS) and an aqueous receiving solution containing a stabilizing agent (RESOLV). The effect of processing conditions on both particle size and form was investigated. The size of the porphyrin nanoparticles produced via RESS increased in a well-behaved manner from 40 to 80 nm as the preexpansion temperature increased from 40 to 100 degrees C, independent of porphyrin concentration, degree of saturation, and preexpansion pressure. RESOLV of TBTPP + CO(2) solutions was investigated both for minimizing particle growth in the free jet and for the prevention of particle agglomeration. Anionic, nonionic, and polymeric stabilizing agents for the aqueous receiving solution were considered. Expansion into a 0.05 wt % SDS solution produced nanorods 50-100 nm in diameter with an aspect ratio of 3-5. RESOLV in a 0.025 wt % Pluronic F68 solution produced well-dispersed, individual, spherical nanoparticles averaging 23 +/- 10 to 32 +/- 10 nm in diameter, independent of the rapid expansion processing conditions selected. Furthermore, the resulting nanoparticle suspensions were stable, with particle sizes remaining unchanged after several months. However, some particle agglomeration occurred at higher (i.e., 1 wt % TBTPP in CO(2)) concentrations. Contact-angle measurements on solid TBTPP compacts with the tested receiving solutions indicate that a moderate wetting agent such as Pluronic F68 is most effective for preserving the size and form of the porphyrin nanoparticles produced by RESOLV. Finally, the fact that nanoparticles are produced from RESS of TBTPP, in contrast with other organics for which microparticles are produced, can be explained in terms of the high melting point of TBTPP (388 degrees C), which results in a solid-state diffusion coefficient of TBTPP low enough so that particle coalescence is significantly reduced in the free jet.     

Co-precipitation of asiatic acid and poly(<Emphasis Type="SmallCaps">l</Emphasis>-lactide) using rapid expansion of subcritical solutions into liquid solvents

Poly(l-lactide) (PLLA) nanoparticles loaded with asiatic acid (AA) were successfully produced by rapid expansion of a subcritical solution into an aqueous receiving solution containing a dispersing agent. A mixture of carbon dioxide (CO₂) and ethanol (EtOH) with a weight ratio of 1:1 was used as the solvent for AA and PLLA. Two surfactants, Pluronic F127 and sodium dodecyl sulfate were employed. The former was found to be more effective for stabilizing AA-loaded PLLA nanoparticles, as a rapid expansion into a 0.1 wt% Pluronic F127 solution produced a stable nanosuspension consisting mainly of well-dispersed, individual nanoparticles. The effects of rapid expansion-processing conditions—AA to PLLA weight ratio and pre-expansion temperature (T_pre)—on the size and morphology of composite nanoparticles, and the loading capacity and entrapment efficiency of AA in PLLA nanoparticles, were systematically investigated. It was found that AA-loaded PLLA nanoparticles with a size range of 30–100 nm were consistently fabricated by rapid expansion at T_pre of 70–100 °C and AA to PLLA weight ratios of 1:2 and 1:4, and with a constant pre-expansion pressure of 330 bar. The T_pre and AA to PLLA weight ratio had no significant effects on the size of the nanoparticles. The AA to PLLA weight ratio is a controlling parameter for both the loading capacity and the entrapment efficiency of AA in PLLA nanoparticles. The loading capacity and entrapment efficiency increased from 8–11 to 16–21 wt%, and 38–57 to 50–62 wt%, respectively, when the AA to PLLA weight ratio changed from 1:4 to 1:2. However, increasing the T_pre from 70 to 100 °C decreased both the loading capacity and entrapment efficiency of AA in PLLA nanoparticles by ~20–30%.     

An experimental investigation of P–N diode electrical characteristics by soft X-ray annealing method

We present new experimental results for the electrical behaviors of P–N junction diodes irradiated by X-rays. The current–voltage (I–V) characteristics of the P–N junction diodes were measured at room temperature. The reverse and forward current before and after irradiation can be explained relative to the following parameters: carrier generation lifetime (τ_g), ideality factor (n), series resistance (R_s), and sheet resistance (ρ). After irradiation at 40 and 55 keV, a small increment in the diode leakage current was seen, while at 70 keV of exposure, the leakage current was slightly decreased. On the other hand, the forward current was dramatically increased by about three orders of magnitude. In addition, the series resistance of the diodes was confirmed to be positively modified by the use of the soft X-ray annealing method.