Probabilistic Model Describes Clogging During Filtration of Non-Colloidal Suspensions
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This suggests that these films do not show similar properties as bulk glass of the same composition, according to the researchers. More than one fundamental type of intergranular film forms on alumina grain boundaries and promotes diffusional transport, they said. JOAN J. CARVAJAL
Lotus-Like Superhydrophobic Surfaces Produced from MetalSalt Precursors Generally, superhydrophobic surfaces have water contact angles larger than 150°. In nature, this unusual characteristic is observed on lotus and rice leaves. Artificial superhydrophobicity is generally realized after mechanical roughening or lowering of the surface energy by chemical methods. Typically, these methods require expensive materials or are time-consuming. Recently, S. Chen, C. Hu, L. Chen, and N. Xu of the College of Chemistry and Chemical Engineering at Nanjing University of Technology in Nanjing, China have reported a simple method to produce superhydrophobic surfaces using inexpensive metal alkanethiolates. In their publication in a recent issue of Chemical Communications (p. 1919; DOI: 10.1039/ b700994a), the researchers suggest their method produces surfaces that mimic the natural superhydrophobicity of lotus leaves. The superhydrophobic surfaces were produced by reacting metal salts with alkanethiols. The alkanethiols consist of low surface energy, long chain alkyl groups. Initially, metal salts (cadmium or zinc) were directly reacted with n-dodecanethiol (1:2 molar ratio) to produce metal dithiolates with yields >95%. The resulting metal dodecanethiolate thin film (50 μm thick) was dried overnight after evaporation of ethanol at 25°C. Hydrophobicity was observed after the reaction was completed. Scanning electron microscopy (SEM), x-ray diffraction (XRD), and water contact angle (CA) measurements were performed on the samples. SEM analysis showed the cadmium dodecanethiolate film surface consisted of flower-like spheres ranging from 5–37 μm in diameter. Individual spheres were composed of a number of microrods with average diameters of ~200 nm. The cadmium dodecanethiolate surface morphology is similar to natural lotus-like micro- and nano-hierarchical structures, which are related to the structure of the cadmiumsalt precursor. XRD analysis demonstrates the cadmium dodecanethiolate films form highly crystalline, layered structures. Wetting experiments result in water CAs of 154° and 153° for (cadmium, zinc) dodecanethiolate films, respectively. The zinc
dodecanethiolate films possessed a leaflike pattern that is related to the zinc-salt precursor with diameters ranging over 2.5–5.0 μm. The researchers said their method is a convenient, inexpensive approach for producing superhydrophobic surfaces with rough hierarchical micro/ nanostructures. Chen and co-workers said this technique may also be applicable for self-cleaning surfaces. JEREMIAH T. ABIADE
Probabilistic Model Describes Clogging During Filtration of Non-Colloidal Suspensions The flow of suspensions through filters and porous structures—such as in liquid purification and drilling well pro
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