Fractional proton distributions

Table II. Fractional Proton Distributions of Green River Asphaltenes by NMR...

Distribution of protons by type and overall aromatic/aliphatic proton ratios for the original fractions and bottoms products, as determined by proton nmr. Proton distribution for fraction D and the whole coal are not included as these materials were only partly soluble and the resultant spectra were not representative of the whole material. 

Table II. Proton Distribution and Structural Parameters of Coal-Liquid Fractions (7)...

Proton distribution of an initial 50% H+, 50% NH4+ fraction following introduction of 0.25 A/ cm current density into Nafion 1100,180- im thickness at indicated time intervals from. 05 to 100 s. Anode at left (x = 0) and cathode at right (x = 1). 

Proton distribution in membrane at a fixed current density of 0.09 A/cm for various thicknesses, with initial 50% initial proton ion fraction. The distribution would be the same if we fixed the thickness and varied the current density. 

Previously, we saw how the diffusion and migration fluxes varied across the membrane in the absence of water effects. If we include water effects but maintain uniform X across the membrane, the water will have little effect. Now, we impose a water activity gradient by setting to 11 and Xq to 14. In the absence of current, this will cause water to flow toward the anode. Let us look at the same case as in Figure 8.9 at 0.25 A/cm, shown in Figure 8.10. The potential at the cathode was -45 mV when X was constant, but was -66 mV when Xj was 11. Because the forward flow of protons was impeded by the backflowing water, its migration flux is decreased while its diffusion flux is increased. The ion fraction yn distribution is the same in both cases. 

The exchange of protons between pure water (no cations oflier than protons) and an amphoteric metal oxide interface will produce three different types of surface site (1) unprotonated anionic sites each with a unit negative valence, (2) monopro-tonated nonionic sites each with a zero valence, and (3) diprotonated cationic sites each with a unit positive valence. Given sufficient time to reach equilibrium, die proton exchange will produce a surface in which the number of each type of site and the number of protons in solution becomes constant. To specify the stoichiometry of this equilibrium proton distribution, the total number of surface sites will be de-sianted as n, with the number of each specific type of surface site designed as (1) Q, for unprotonated anionic sites, (2) sOH for monoprotonatednonionic sites, and (3) soH diprotonated cationic sites. The surface site mole fraction can diere-fore be defined relative to nJ as ... 

The equilibrium constant for this reaction depends on the stability constants of the ionophore-M+ complexes and on the distribution of ions in aqueous test solution and organic membrane phases. For a membrane of fixed composition exposed to a test solution of a given pH, the optical absorption of the membrane depends on the ratio of the protonated and deprotonated indicator which is controlled by the activity of M+ in the test solution (H,tq, is fixed by buffer). By using a to represent the fraction of total indicator (Ct) in the deprotonated form ([C]), a can be related to the absorbance values at a given wavelength as... 

In certain regions of the density-temperature plane, a significant fraction of nuclear matter is bound into clusters. The EOS and the region of phase instability are modified. In the case of /3 equilibrium, the proton fraction and the occurrence of inhomogeneous density distribution are influenced in an essential way. Important consequences are also expected for nonequilibrium processes. 

Donor and acceptors can be covalently linked using a chemical spacer. Assume that we have the same D-A pair Eosin-Phenol Red. In this case we will have a mixture of two linked donor-acceptor species (Eosin-Phenol Red protonated and Eosin-Phenol Red unprotonated) characterized by the same distance distribution and different critical distances (ftoi = 28.3 A and Rm = 52.5 A) for FRET. A distribution of D- to -A distances will be present because the linker is typically flexible. The fractional intensity of the first species at time t = 0 is gi and that of the second species is (1 - 1). The fractional intensity at time t = 0 is equal to fractional concentration of each form, which can be in case of pH indicator (Phenol Red) calculated using Eq. (10.31). The donor fluorescence intensity decay of the mixture is described by the equation... 

Weber and Newman do the averaging by using a capillary framework. They assume that the two transport modes (diffusive for a vapor-equilibrated membrane and hydraulic for a liquid-equilibrated one) are assumed to occur in parallel and are switched between in a continuous fashion using the fraction of channels that are expanded by the liquid water. Their model is macroscopic but takes into account microscopic effects such as the channel-size distribution and the surface energy of the pores. Furthermore, they showed excellent agreement with experimental data from various sources and different operating conditions for values of the net water flux per proton flux through the membrane. 

Fig. 14. Dependence of the relaxation times T2. and the fractions of protons with different mobility (f.) for unsaturated polyester on the curing time, as measured from broad line NMR ( ), Hahn spin-echo ( ) and Carr-Purcell pulse sequence (O)- Symbol x indicates the initial distribution of styrene and unsaturated polyester protons (adapted from Ref. S5))...

S0l., So2 and SHlo refer to the respective source terms owing to the ORR, e is the electrolyte phase potential, cGl is the oxygen concentration and cHlo is the water vapor concentration, Ke is the proton conductivity duly modified w.r.t. to the actual electrolyte volume fraction, Dsa is the oxygen diffusivity and is the vapor diffusivity. The details about the DNS model for pore-scale description of species and charge transport in the CL microstructure along with its capability of discerning the compositional influence on the CL performance as well as local overpotential and reaction current distributions are furnished in our work.25 27,67... 

The proton nmr spectrum of fraction 2 of the S02 solubles resembles that of asphaltenes as reported by other workers (1). The elemental composition and the GPC size distribution agrees with the values published for coal derived asphaltenes (1,3). Fractions 3 and 4 of the S02-solubles were separated and identified by GC-MS (see Figures 4 and 5). These fractions contain only a small amount of alkanes. The components are listed in Tables I and II. 

The copolymer can be further fractionated by precipitation from acetone solution to n-hexanc at room temperature. In each case, only the first fraction should be used to obtain narrowly distributed high molar mass copolymer chains for LLS measurement, ll NMR can be used to characterize the copolymer composition. The ratio of the peak areas of the methine proton of the isopropyl group in NIPAM and the two protons neighboring the carbonyl group in VP can be used to determine the VP content. The composition of each NIPAM-co-VP copolymer was found to be close to the feeding monomer ratio prior to the copolymerization. The nomenclature used hereafter for these copolymers is NIPAM-co-VP/x/y, where x andy are the copolymerization temperature (°C) and the VP content (mol%), respectively. The solution with a concentration of as low as 3.0 x 10-6 g/mL can be clarified with a 0.45 cm Millipore Millex-LCR filter to remove dust before the LLS measurement. The resistivity of deionized water used should be close to 18 M 2 cm. The chemical structure of poly(NIPAM-co-VP) is as follows (Scheme 2). 

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