Charging, surface parameter

Surface electron charge density can be described in tenus of the work fiinction and the surface dipole moment can be calculated from it ( equatiou (Bl.26.30) and equation (B1.26.31)). Likewise, changes in the chemical or physical state of the surface, such as adsorption or geometric reconstruction, can be observed through a work-fimction modification. For studies related to cathodes, the work fiinction may be the most important surface parameter to be detenuined [52]. 

Molecular surface parameter for calculating solvation energies Nuclear charge, exact... 

Manning s theory does not take the local effective dielectric constant into consideration, but simply uses the a value of bulk water for the calculation of E,. However, since counterion condensation is supposed to take place on the surface of polyions. Manning s 2, should be modified to E, by replacing a with aeff. The modified parameters E, is compared with E, in Table 1, which leads to the conclusion that the linear charge density parameter calculated with the bulk dielectric constant considerably underestimates the correct one corresponding to the interfacial dielectric constant. 

As the logarithm of 1-octanol-water partition coefficient (log P) describes the hydrophobicity of molecules and the retention of solutes in RP-HPLC depends on the hydrophobicity, a strong correlation can be expected between the log V value and the retention of solutes in RP-HPLC. Besides log P, a considerable number of physicochemical parameters have been tested for their capacity to predict retention in RP-HPLC. Thus, Snyder s polarity index, fraction of positively and negatively charged surface area, molecular bulkiness, nonpolar surface area, electron donor and acceptor capacity, various ster-ical parameters, and the energy of highest occupied molecular orbit have all been included in QSRR calculations. 

At low electric fields [0(lV/cm)] the speed (U) of the particles is directly proportional to the applied field ( ) and hence we can define a parameter called the electromobility ( x) of the particles, given by U/E. Using the Poisson-Boltzmann theory of the diffuse electrical layer next to a charged surface, a simple relationship between p and V /o can be... 

The situation is similar to the success of the traditional Poisson—Boltzmann approach its ability in describing, at least qualitatively, and many times even quantitatively, the behavior of most colloidal systems probably resides in the use of at least one adjustable parameter (surface charge, surface potential, recombination constant and so on) in the fitting of the experimental results. If that parameter could be accurately measured, one would have to address the inaccuracies generated by the mean field treatment itself. 

Having emphasized the importance of the pH parameter, it should be recognized that its measurement is in itself a difficult task [90]. When the surface is charged, the overall ion concentrations are not constant close to the oxide-fluid interface. For instance, above the IEP, i.e. for negatively charged surfaces, there is an increase in cation and proton concentrations at the surface. Therefore, the pH is lower than in the bulk of the solution. The situation is reversed at a pH lower than the IEP. This is a typical compensation effect of the pH. 

The population of charged surface sites is determined by the first and second surface protonation constants of the oxide (AG°ads e+4 and AG°ads H+ 2). These terms depend, in turn, on the crystal-chemical parameter, s/r, which is the Pauling bond strength34 per metal-OH bond length, and on l/ek.35 37... 

Following a similar approach but using a smaller data set of 369 compounds, Ivanciuc et al. correlated their liquid viscosity (10 Pa s) at 298 K with a mixed set of descriptors to obtain Eq. [48]. This involves three QM descriptors, one topological, and one constitutional descriptor. The QM descriptors were calculated with the AMI Hamiltonian in AMPAC, and CODESSA was used to calculate the descriptors and perform the statistical analyses. The HDCA2 parameter is the same HBD charged surface area used in Eq. [46]. The maximum electrophilic reactivity index, Ep, for a carbon atom is defined by X/ lumo,/A lumo+ 10), with the summation over the valence AOs on a carbon atom in the LUMO. The maximum AO electronic population, Y, models the molecular nucleophilicity and is defined by... 

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