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81.
Karl D. Hammond Geoffrey A. Tompsett Scott M. Auerbach W. Curtis Conner 《Journal of Porous Materials》2007,14(4):409-416
We present a non-destructive, reusable apparatus with which to measure physical adsorption isotherms of intact porous membranes.
We developed a two-piece sample container to make reliable sorption measurements of porous membranes, the properties of which
may differ from those of powders due to crystal intergrowth. This novel system employs a resealable container that can be
immersed in a cryogenic bath, into which tubular, planar, or other porous membranes and films may be placed. Detailed sorption
isotherms, including high-resolution adsorption in the low pressure (micropore-filling) region, are shown for MFI-type zeolite
membranes grown on two types and configurations of α-alumina support. 相似文献
82.
Many high Miller index metals surfaces are naturally chiral, offering opportunities for performing enantiospecific chemistry. Previous theoretical treatments of adsorption on these surfaces have used surfaces truncated from bulk crystals. This paper examines the effect of surface relaxation on enantiospecific adsorption on chiral Pt surfaces by using relaxed surface structures determined using density functional theory. 相似文献
83.
Mixtures of 90, 80, and 70 percent by weight bisphenol-A-polycarbonate (PC) and 10, 20, and 30 percent by weight styrene maleic anhydride (SMA) copolymer were melt-blended in a single screw extruder. Differential scanning calorimetry (DCS) and scanning electron microscopy (SEM) were used to determine the miscibility of the blends. The viscosity, as a function of shear rate and temperature, was measured by an Instron capillary viscometer. The notched impact strength as a function of temperature was measured by an Izod impact tester. The results of DSC showed two glass transition temperatures which merged slightly towards each other, indicating marginal miscibility of these blends. There was a decrease in viscosity as the fraction of SMA copolymer was increased. The most significant decrease occurred with the initial addition of SMA copolymer. The viscosity also decreased with increases in temperature. The impact strength of the blends was also dependent on SMA copolymer content. The blends showed six to ten times lower impact strengths at room temperature than the 100 percent polycarbonate. SEM analysis helped to determine the reason why the impact strength was lower for the blends. High magnification showed the presence of SMA copolymer inclusions dispersed throughout the PC matrix. These inclusions, which increased in size as SMA copolymer content was increased, acted as defects in the system. 相似文献
84.
Sihua Xu Glenn W. Patterson William R. Lusby Kathy M. Schmid Thomas A. Salt 《Lipids》1990,25(1):61-64
Twenty-one species in the Chenopodiaceae were analyzed for sterol composition. In ten of eleven species ofChenopodium, the major desmethylsterols were Δ7-sterols accompanied by lower proportions of Δ5-sterols. InC. fremontii this pattern was reversed. The sterol profiles of five species ofAtriplex were characterized by the coexistence of Δ7- and Δ5-sterols in ratios of 0.3∶1 to 0.4∶1. MaleAtriplex plants contained higher proportions of Δ5-sterols than femaleAtriplex plants. OneCeratoides and twoSalicornia species contained Δ5-sterols as their predominant sterols. 相似文献
85.
Ashwin Kumar Vutha Benyamin Davaji Chung Hoon Lee Glenn M. Walker 《Microfluidics and nanofluidics》2014,17(5):871-878
We demonstrate the use of heat to count microscopic particles. A thermal particle detector (TPD) was fabricated by combining a 500-nm-thick silicon nitride membrane containing a thin-film resistive temperature detector with a silicone elastomer microchannel. Particles with diameters of 90 and 200 μm created relative temperature changes of 0.11 and ?0.44 K, respectively, as they flowed by the sensor. A first-order lumped thermal model was developed to predict the temperature changes. Multiple particles were counted in series to demonstrate the utility of the TPD as a particle counter. 相似文献
86.
A series of organic/inorganic hybrid (OIH) films were prepared using cellulose acetate (CA) as the organic component and tetraethyl orthosilicate (TEOS) as the inorganic component. The chemical, morphological, and mechanical properties of these films were evaluated with a variety of analytical techniques. The results of these evaluations showed that crosslinked CA OIH films were formed during the sol-gel reactions. The structure of OIH films was very sensitive to the CA/TEOS ratio and film formation conditions. All of the films with added TEOS were two phase on a molecular level, i.e., inorganic TEOS domains surrounded by a CA matrix. Under some film formation conditions the presence of TEOS, a nonsolvent for CA, led to solvent/nonsolvent phase separation on the micron scale. © 1995 John Wiley & Sons, Inc. 相似文献
87.
Haiqing?Liu S.?Kay?ObendorfEmail author Michael?J.?Leonard Timothy?J.?Young Michael?J.?Incorvia 《Journal of surfactants and detergents》2005,8(4):311-317
The adsorption of aroma chemicals on cotton fabric was studied relative to the surfactant concentration, surfactant type,
water solubility, and fiber morphology. The adsorption increased with increasing surfactant concentration to a maximum near
the critical micelle concentration, then decreased with further increases in surfactant concentration. The adsorption also
was found to be highly dependent on the fiber surface area and pore structure; dramatic differences were observed between
untreated and mercerized cotton fabric and are believed to be due to morphological differences. Cationic and anionic surfactants
increased the aroma chemical adsorption, which varied with surfactant type, with cetyltrimethylammonium chloride (CTAC)>sodium
dodecyl sulfate (SDS)>H2O. Water solubility also influenced adsorption; in most cases, adsorption increased with water solubility. In addition, adsorption
was also influenced by chemical structure and hydrophobic interactions. The adsorption of aroma chemicals on cotton fabric
can be attributed to the aqueous solution being physically held in capillaries and pore structures within the fibular structure
of cotton fiber and also to molecular interactions among the aroma chemical molecules, surfactants, and cotton substrate. 相似文献
88.
The interaction of cholesterol with ceramides containing α-hydroxy fatty acyl chains (hydroxyceramides) has been studies as
a foundation for characterizing the lipid bilayers of thestratum corneum. A relatively large quantity of cerebrosides was obtained from bovine brain and converted to ceramides through removal of
the carbohydrate side chain. The ceramides were separated based on the absence or presence of hydroxy fatty acyl chains. The
lyophilized hydroxyceramides showed a broad melting region at 92°C. Hydroxyceramides dispersed in water produced a relatively
narrow, thermotropic transition at 75°C. The effect of cholesterol on this thermotropic phase transition of hydroxyceramides
was determined by differential scanning calorimetry. With respect to the main transition, cholesterol caused a broadening
of the phase transition at relatively low levels as well as a decrease in the peak transition temperature. The presence of
cholesterol at levels in excess of 7 wt% gave rise to an additional low-temperature transition at 55°C. Upon immediate rescanning,
this transition was exothermic, but with increasing incubation time the area under the excess heat capacity curve as a function
of temperature became smaller. After two days or more, the transition observed was endothermic. At cholesterol levels between
40 and 50 wt%, multiple peaks were observed. From comparisons with related systems, the cooperative thermal transitions of
hydroxyceramides with cholesterol are suggested to result from changes in hydrogen bonding or be due to phase separation.
The composition of isolated brain ceramides is being compared with that reported for thestratum corneum. 相似文献
89.
A series of high performance, experimental carbon/graphite fibers was intercalated and examined with respect to their metallic conductivity behavior by resistivity and magnetoresistance versus temperature measurements. One fiber was a polyacrylonitrile (PAN)-type precursor and three were pitch base precursors. All four types showed substantially similar behavior in the pristine state with respect to room temperature resistivity and the sign and magnitude of the temperature coefficient of resistivity. After intercalation with either nitric acid or nitric acid followed by AsF5, the PAN-based fibers displayed a resistivity versus temperature behavior qualitatively similar to their pristine counterparts but displaced to lower resistivity. On the other hand, the pitch fibers with the same intercalation treatment exhibited metallic behavior (a positive temperature coefficient of electrical resistivity and a small magnetoresistance). These manifestations of metallic behavior are usually indicative of some three dimensional graphite structure in the carbon fibers. 相似文献
90.
Timothy J. Bunning Hong G. Jeon Ajit K. Roy Kristen M. Kearns Barry L. Farmer Walter W. Adams 《应用聚合物科学杂志》2003,87(14):2348-2355
The thermal and mechanical properties of polyurethane‐infiltrated carbon foam of various densities were investigated. By combining the high thermal conductivity of the carbon foam with the mechanical toughness of the pure polyurethane, a mechanically tough composite (relative to the unfilled foam) that could be used at higher temperatures than the polyurethane's degradation was formed. Both the tensile strength and the modulus increased by an order of magnitude for the composites compared to unfilled foam, while the compressive and shear strengths and moduli of the composites approached values exhibited by pure polyurethane. At both 300 and 400°C, the rectangular blocks of pure polyurethane lost their mechanical integrity due to decomposition in air. Thermogravimetric analysis confirms substantial initial weight loss above 290°C. Filled carbon foam blocks, however, maintain their mechanical integrity at both 300 and 400°C indefinitely, although the bulk of the rectangular block mass is polyurethane. Three different carbon foam densities are examined. As expected, the higher density foams show greater heat transfer. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 2348–2355, 2003 相似文献