This study examines the effect of environmental and experimental conditions, such as temperature and time, on the wettability properties of titania nanotube (TNT) surfaces fabricated by anodization. The fabricated TNTs are 60-130 nm inner diameter and 7-10 µm height. One-microliter water droplets were used to define the wettability of the TNT surfaces by measuring the contact angles. A digital image analysis algorithm was developed to obtain contact angles, contact radii and center heights of the droplets on the TNT surfaces. Bare titanium foil is inherently less hydrophilic with approximately 60°-80° contact angle. The as-anodized TNT surfaces are more hydrophilic and annealing further increases this hydrophilic property. Furthermore, it was found that the TNT surface became more hydrophobic when aged in air over a period of three months. It is believed that the surface wettability can be changed due to alkane contamination and organic contaminants in an ambient atmosphere. This work can provide guidelines to better specify the environmental conditions that changes surface properties of TNT surfaces and therefore affect their desirable function in specific applications such as orthopedic implants.
We report on the wetting dynamics of a 4.3 μL deionized (DI) water droplet impinging on microtextured aluminum (Al 6061) surfaces, including microhole arrays (hole diameter 125 μm and hole depth 125 μm) fabricated using a conventional microcomputer numerically controlled (μ-CNC) milling machine. This study examines the influence of the texture area fraction ϕ(s) and drop impact velocity on the spreading characteristics from the measurement of the apparent equilibrium contact angle, dynamic contact angle, and maximum spreading diameter. We found that for textured surfaces the measured apparent contact angle (CA) takes on values of up to 125.83°, compared to a CA of approximately 80.59° for a nontextured bare surface, and that the spreading factor decreases with the increased texture area fraction because of increased hydrophobicity, partial penetration of the liquid, and viscous dissipation. In particular, on the basis of the model of Ukiwe and Kwok (Ukiwe, C.; Kwok, D. Y. Langmuir 2005, 21, 666), we suggest a modified equation for predicting the maximum spreading factor by considering various texturing effects and wetting states. Compared with predictions by using earlier published models, the present model shows better agreement with experimental measurements of the maximum spreading factor.
The present study investigates the optical characteristics and the spectral and angular responses of a Kretschmann surface plasmon resonance (SPR) sensor configuration that is widely used in biological and chemical sensing applications. In order to examine the influence of wave interference and optical properties of thin films on angular variation of reflectance at different incident angles, the Kretschmann SPR configurations made of gold films with 30, 52, and 70 nm thicknesses were fabricated and the reflectance was detected using a 633 nm He-Ne laser, -2 rotation stages, and a silicon pin photo-detector. In particular, this study involved the numerical analysis of angular and spectral variation of reflectance estimated using the characteristic transmission matrix (CTM) method. It was found that the SPR sensitivity became highly dependent on the gold film thickness, indicating that in the thinner gold film case, the reflectance was recovered slowly after the SPR angle, whereas as the gold film thickness increased, the magnitude difference between the maximum and the minimum reflectance measured near the SPR angle was smaller than in other cases. From the numerical analysis, it was shown that the phase shift is the most sensitive physical parameter for SPR sensor by comparing estimated FWHM values of reflectance, phase shift, and enhancement of magnetic field intensity. Therefore, it was concluded that an appropriate metal thickness of around 50 nm was found for higher sensitivity. Keywords: Kretschmann surface plasmon resonance (SPR) sensor, characteristic transmission matrix (CTM) method, full width at half maximum (FWHM), phase shift, enhancement of magnetic field intensity
bHydrogenogenic CO oxidation (CO ؉ H 2 O ¡ CO 2 ؉ H 2 ) has the potential for H 2 production as a clean renewable fuel. Thermococcus onnurineus NA1, which grows on CO and produces H 2 , has a unique gene cluster encoding the carbon monoxide dehydrogenase (CODH) and the hydrogenase. The gene cluster was identified as essential for carboxydotrophic hydrogenogenic metabolism by gene disruption and transcriptional analysis. To develop a strain producing high levels of H 2 , the gene cluster was placed under the control of a strong promoter. The resulting mutant, MC01, showed 30-fold-higher transcription of the mRNA encoding CODH, hydrogenase, and Na ؉ /H ؉ antiporter and a 1.8-fold-higher specific activity for CO-dependent H 2 production than did the wild-type strain. The H 2 production potential of the MC01 mutant in a bioreactor culture was 3.8-fold higher than that of the wild-type strain. The H 2 production rate of the engineered strain was severalfold higher than those of any other COdependent H 2 -producing prokaryotes studied to date. The engineered strain also possessed high activity for the bioconversion of industrial waste gases created as a by-product during steel production. This work represents the first demonstration of H 2 production from steel mill waste gas using a carboxydotrophic hydrogenogenic microbe. Carbon monoxide (CO) is highly toxic to most living creatures, but it can be utilized by microorganisms as an energy and carbon source for the production of fuels and chemicals, such as acetate, butyrate, ethanol, butanol, and H 2 . Among those carboxydotrophic microbes, CO-dependent H 2 production has been observed in three distinct groups, i.e., mesophilic bacteria, thermophilic bacteria, and hyperthermophilic archaea (1-3). Generally, growth rates of the mesophilic hydrogenogenic bacteria on CO are low, and high levels of CO are inhibitory. Predominant within this group are nonsulfur purple bacteria, including Rubrivivax gelatinosus and Rhodospirillum rubrum, which require light for optimal cell growth. Although Rhodopseudomonas palustris P4 is capable of hydrogenogenic CO conversion in the dark, it does not grow under this condition (4). Nonphototrophic Citrobacter strain Y19 also converts CO to H 2 , but it only grows slowly under anaerobic conditions and an aerobic growth phase is required to generate sufficient biomass before the anaerobic CO conversion phase (5). The second group includes thermophilic, hydrogenogenic bacteria isolated from freshwater and marine environments with temperatures ranging from 40 to 85°C. Carboxydothermus hydrogenoformans, Carboxydocella thermautotrophica, Thermosinus carboxydivorans, and Caldanaerobacter subterraneus subsp. pacificus are capable of chemolithotrophic growth on high concentrations of CO. The third group includes two hydrogenogenic CO-converting archaea, Thermococcus sp. strain AM4 and Thermococcus onnurineus NA1 (6, 7). Both strains are hyperthermophiles isolated from deep-sea hydrothermal vents and can grow on 100% CO (8).Anaerobic carboxydotroph...
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