Electrostatic balance parameter

The knowledge of the values of the net charges allows, for example, the calculation of the standard deviation o for the positive and negative charges, for the negative charges and then calculation of the electrostatic balance parameter descriptor (Murray et al. 1993). 

CT+, G- and Gtot being the positive, negative and total variances of the electrostatic potential) and v being an electrostatic balance parameter defined as v =... 

The data were obtained in an electrostatic balance, and phase functions were recorded to determine the droplet size as a function of time. The slopes of the three data sets are S12 = - 7.54 x 10 (/an)Vs, S,3 = — 1.70 X 10 (/im)Vs, and S14 = — 1.10 x 10 ( m)Vs. From these and additional data obtained at different temperatures, Ravindran et al. reported aoBS = 9.97 0.26A, Sobs/ b = 688 72 K, and pges(293 K) = 207//Pa. They also reported Lennard-Jones parameters and vapor pressures measured in this way for dibutyl phthalate and dioctyl phthalate. 

Early MEP-based parameters considered included surface area (A), If, and v. Flere II is a measure of local polarity, and is a measure of electrostatic interaction tendency. Larger values imply larger charge separation leading to greater electrostatic interaction. Electrostatic interactions are also described by v, which is a measure of electrostatic balance. The three charge related variables are defined in terms of the surface electrostatic potential difference, 8U at the ith point, Eq. [33],... 

The parameter redundancy is also the reason that care should be exercised when trying to decompose energy differences into individual terms. Although it may be possible to rationalize the preference of one conformation over another by for example increased steric repulsion between certain atom pairs, this is intimately related to the chosen functional form for the non-bonded energy, and the balance between this and the angle bend/torsional terms. The rotational banier in ethane, for example, may be reproduced solely by an HCCH torsional energy term, solely by an H-H van der Waals repulsion or solely by H-H electrostatic repulsion. Different force fields will have (slightly) different balances of these terms, and while one force field may contribute a conformational difference primarily to steric interactions, another may have the... 

Lux (1939) introduced the symbol pO (note it is not an exponent like pH) to quantify the acid-base balance in a glass, and various attempts have been made to obtain values for this parameter. All are based on the electronegativity of the cation or a related characteristic, such as electrostatic field strength (Volf, 1984). 

Hirshfeld (1984) found the electrostatic charge balance at the F nuclei, based on the experimental deformation density, to be several times more repulsive (i.e., anti-bonding) than that of the promolecule. Very sharp dipolar functions at the exocyclic C, N, and F atoms, oriented along the local bonds, were introduced in a new refinement in which the coefficients of the sharp functions were constrained to satisfy the electrostatic Hellmann-Feynman theorem (chapter 4). The electrostatic imbalance was corrected with negligible changes in the other parameters of the structure. The model deformation maps were virtually unaffected, except for the innermost contour around the nuclear sites. 

The main problem that the early workers identified with the DLVO theory was that it could not explain how the (i-value varied with the electrolyte concentration c. The observed behavior was that d was inversely proportional to the square root of c, whereas the DLVO theory predicted a much more rapid variation. The origin of this fault is that DLVO theory explains the stable interplate separation in the gel phase as arising from a balance between an electrostatic repulsion, which does depend on c as the inverse square root, and a van der Waals attraction that is more or less independent of the salt concentration. I started studying the gels by neutron diffraction and extended the earlier results to a much wider range of salt concentrations. There was no way the DLVO theory could be made to fit the data, even when the van der Waals force was introduced with an adjustable parameter. 

Various empirical and chemical models of metal adsorption were presented and discussed. Empirical model parameters are only valid for the experimental conditions under which they were determined. Surface complexation models are chemical models that provide a molecular description of metal and metalloid adsorption reactions using an equilibrium approach. Four such models, the constant capacitance model, the diffuse layer model, the triple layer model, and the CD-MUSIC model, were described. Characteristics common to all the models are equilibrium constant expressions, mass and charge balances, and surface activity coefficient electrostatic potential terms. Various conventions for defining the standard state activity coefficients for the surface species have been... 

The purely electrostatic diffuse layer model often underestimates the affinity of the counterions to the surface. In the Stem model, the surface charge is partially balanced by chemisorbed counterions (the Stem layer), and the rest of the surface charge is balanced by a diffuse layer. In the Stern model, the interface is modeled as two capacitors in series. One capacitor has a constant capacitance (independent of pH and ionic strength), which represents the affinity of the surface to chemisorbed counterions, and which is an adjustable parameter the relationship between a, and Vd in the other capacitor (the diffuse layer) is expressed by Equation 2.18. A version of the Stern model with two different values of C (below and above pHg) has also been used. The capacitance of the Stem layer reflects the size of the hydrated counterion and varies from one salt to another. The correlation between cation size and Stern layer thickness was studied for a silica-alkali chloride system in [733]. Ion specificity of adsorption on titania was discussed in terms of differential capacity as a function of pH in [545]. The Stern model with the shear plane set at the end of the diffuse layer overestimated the absolute values of the potential of titania [734]. A better fit was obtained with the location of the shear plane as an additional adjustable parameter (fitted separately for each ionic strength). Chemisorption of counterions can also be quantified within the chemical model in terms of expressions similar to the mass law (Section 2.9.3.3). 

Reverse miceUes have been applied in the separation of amino acids and proteins. The separation is based on the balance between electrostatic forces and hydrophobic interactions [120]. The pH value is a crucial parameter determining this balance. If reversed miceUes are applied in LMs, then the underlying interactions are determined by interfacial partition coefficients of the amino acids/proteins separated, that is, hydrophobicity of the compounds separated, ionic strength of the feed and stripping solutions, the chemical nature of the electrolytes present, and the intertacial curvature of the amphiphilic film [121]. Changing the above-mentioned conditions, the overaU charge of the reverse miceUe can be altered, and so the separation conditions can be manipulated [122]. 

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