Electrostatic potential balance parameter

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],... 

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... 

When the surface is taken as ideal, that is, flat and homogeneous, the physical quantities depend only on the distance a from the surface. The surface imposes boundary conditions on the polymer order parameter fix) and electrostatic potential fix). In thermodynamic equihhrium, all charge carriers in solution should exactly balance the surface charges (charge neutrality). The Poisson-Boltzmann Equation (55), the self-consistent field Equation (56), and the boundary conditions uniquely determine the polymer concentration profile and the electrostatic potential. In most cases, these two coupled nonlinear equations can only he solved numerically. 

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 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). 

It turns out that the details of structures with the same framework topology sensitively depend on the partial charges chosen for lattice cations and anions. The difference in relative stability of a- and / -quartz are an example [7]. In view of our interest in the zeolitic chemical bond, the overabundance of potential parameters and the need to properly balance the electrostatic and covalent interactions, a comparison of several predicted and experimental properties is essential. By doing this an accurate determination of potential parameters has become possible. 

Mineral particles may be dispersed in water through repulsive forces which keep the particles apart from each other. The most common forces are electrostatic interactions which arise from ionization of the particles surface. They are opposed by Van der Waal attractions which tend to pull particles together. The most important parameter in this balance of repulsions and attractions is the heigth of the potential barrier of repulsion which results from electrostatic interaction classical DLVO theory indicates that long term stability is ensured if this potential is at least 15 kT (/). 

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