Bulk characterization results

Surface and bulk characterization were carried out using electron spectroscopy for chemical analysis (ESCA or XPS) and x-ray diffraction (XRB). The results will be discussed In relation to methanatlon activity. 

Other electrochemically characterized organometallic V(IV) complexes are rare. The thiolate bridged [Cp(CO)2V(/o,-SR)2V(CO)2Cp] (R = Me, Ft, Ph) have reversible reduction processes that range from —1.89 to —2.01 V versus Cp2Fe/THF in addition to two other irreversible reduction processes at more negative potentials. For R = Me, an oxidation at —0.20 V versus Cp2Fe/THF is reported. Reductive bulk electrolysis results in the decomposition of [Cp CO)2V(fi-SMe)2V(CO)2Cp] by loss of SMe [62]. 

Thus these characterization results demonstrate that polymethacrylic acid does not function in the same manner as polyvinyl alcohol in the emulsion polymerization of vinyl acetate and that the adsorbed polymethacrylic acid can be separated from the bulk polymer, thus distinguishing it from grafted polymer. 

The adsorption of microcystins has been shown to be strongly affected by NOM [78]. In this work the effect, for four microcystin variants, was shown to be a function of the DOC concentration. This is prohahly a result of the direct competitive effect, where the competitive NOM, those compounds approximately the same molecular weight as the microcystins, makes up the hulk of the NOM. Therefore the bulk characterization parameter, DOC, gives an indication of the concentration of competing compounds, where for MIB and geosmin it could not [27, 63, 69]. 

The crystallization of PEO was also unveiled at the level of individual lamellae in ultrathin films (278-280). It was observed that although lamellar growth rates were retarded in films thinner than 200 nm because of interfacial interactions, SFM provided the same qualitative and quantitative information as typically applied bulk characterization techniques on lamellar growth rates, lamellar thicknesses, and melting points. The Hoffman-Weeks extrapolation, the Gihhs-Thompson equation, and the Hoffman-Lauritzen theory were apphed and the results compared favorably to the corresponding hulk data. 

Surface characteristics of these catalysts are reflected on their Sggij, DRS and XPS results. The surface areas of Mn2 and MnC unsupported samples are lower than the corresponding tinZ catalysts. This may be attributed to the differences in the porosity despite the similarity of the chemical nature of these different samples, as pointed out in their bulk characterization. On the other hand, the drop of surface area of all the supported catalysts relative to the support (214 m2 g-1), is most likely due... 

The subscript 0 on 1 implies 0 conditions, a state of affairs characterized in Chap. 1 by the compensation of chain-excluded volume and solvent effects on coil dimensions. In the present context we are applying this result to bulk polymer with no solvent present. We shall see in Chap. 9, however, that coil dimensions in bulk polymers and in solutions under 0 conditions are the same. 

Flame Resistance. Traditionally, small-scale laboratory flammabiUty tests have been used to initially characterize foams (38). However, these do not reflect the performance of such materials in bulk form. Fire characteristics of thermal insulations for building appHcations are generally reported in the form of quaHtative or semiquantitative results from ASTM E84 or similar tunnel tests (39). Similar larger scale tests are used for aircraft and marine appHcations. 

Thickness. Because two fabrics that have identical weight per unit area values may have widely varying bulks, the specification of thickness is essential for properly characterizing a fabric. Fabric thickness has been shown to be direcdy proportional to thermal insulation, or warmth (121). Fabric warmth is the result of the entrapment of air between fibers and yams. A thicker fabric in general allows an increased amount of entrapped air and thus is warmer. 

Although surface treatments, both physical and chemical, have demonstrated the abiUty to alter specific properties of contact lens surfaces, most treatments fail as a result of alteration of bulk lens properties, instabifity of surface treatment, or poor ocular compatibifity. Research is expected to continue in the characterization and modification of contact lens surfaces. 

Membrane Characterization Membranes are always rated for flux and rejection. NaCl is always used as one measure of rejection, and for a veiy good RO membrane, it will be 99.7 percent or more. Nanofiltration membranes are also tested on a larger solute, commonly MgS04. Test results are veiy much a function of how the test is run, and membrane suppliers are usually specific on the test conditions. Salt concentration will be specified as some average of feed and exit concentration, but both are bulk values. Salt concentration at the membrane governs performance. Flux, pressure, membrane geome-tiy, and cross-flow velocity all influence polarization and the other variables shown in Fig. 22-63. 

Four different material probes were used to characterize the shock-treated and shock-synthesized products. Of these, magnetization provided the most sensitive measure of yield, while x-ray diffraction provided the most explicit structural data. Mossbauer spectroscopy provided direct critical atomic level data, whereas transmission electron microscopy provided key information on shock-modified, but unreacted reactant mixtures. The results of determinations of product yield and identification of product are summarized in Fig. 8.2. What is shown in the figure is the location of pressure, mean-bulk temperature locations at which synthesis experiments were carried out. Beside each point are the measures of product yield as determined from the three probes. The yields vary from 1% to 75 % depending on the shock conditions. From a structural point of view a surprising result is that the product composition is apparently not changed with various shock conditions. The same product is apparently obtained under all conditions only the yield is changed. 

An ordering phase transition is characterized by a loss of symmetry the ordered phase has less symmetry than the disordered one. Hence, an ordering process leads to the coexistence of different domains of the same ordered phase. An interface forms whenever two such domains contact. The thermodynamic behavior of this interface is governed by different forces. The presence of the underlying lattice and the stability of the ordered domains tend to localize the interface and to reduce its width. On the other hand, thermal fluctuations favor an interfacial wandering and an increase of the interface width. The result of this competition depends strongly on the order of the bulk phase transition. 

Network properties and microscopic structures of various epoxy resins cross-linked by phenolic novolacs were investigated by Suzuki et al.97 Positron annihilation spectroscopy (PAS) was utilized to characterize intermolecular spacing of networks and the results were compared to bulk polymer properties. The lifetimes (t3) and intensities (/3) of the active species (positronium ions) correspond to volume and number of holes which constitute the free volume in the network. Networks cured with flexible epoxies had more holes throughout the temperature range, and the space increased with temperature increases. Glass transition temperatures and thermal expansion coefficients (a) were calculated from plots of t3 versus temperature. The Tgs and thermal expansion coefficients obtained from PAS were lower titan those obtained from thermomechanical analysis. These differences were attributed to micro-Brownian motions determined by PAS versus macroscopic polymer properties determined by thermomechanical analysis. 

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