Surface electrostatic properties

Electrophoretic light scattering (ELS) is commonly used to measure v. The electrophoretic mobility /r can be calculated from v and the known value of E according to Eq. (I). Theoretical models [ I.7-I0] that describe colloidal electrostatics and hydrodynamics can then be used to relate the measured values of n to particle electrical characteristics including surface charge density and surface electric potential. Because /r depends on the surface electrostatic properties but not particle bulk properties, ELS can characterize surface electrostatic properties exclusively for a wide range of colloidal materials. 

Electrophoretic light scattering (ELS) is a subset of DLS (Section II.C.3) that is commonly used to measure the electrophoretic mobility /a of colloidal particles (Section I.A.2). ELS can be used to probe particle surface electrostatic properties via theoretical models of colloidal electrostatics and hydrodynamics that relate H to particle electrical characteristics. 

This technique has been also applied to characterize flat solid surfaces by initially grinding the flat surfaces into fine powders. However, it is unclear if the surface electrostatic properties of these grinded particles are equivalent to the precrushed surfaces. 

Xiao L, Jia L, Li H, Hong T, Xu SY. Electric force microscopy study of the surface electrostatic property of mbbed pol3dmide alignment layers. Thin Solid Films 2000 370 238-242. 

The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

A surface is that part of an object which is in direct contact with its environment and hence, is most affected by it. The surface properties of solid organic polymers have a strong impact on many, if not most, of their apphcations. The properties and structure of these surfaces are, therefore, of utmost importance. The chemical stmcture and thermodynamic state of polymer surfaces are important factors that determine many of their practical characteristics. Examples of properties affected by polymer surface stmcture include adhesion, wettability, friction, coatability, permeability, dyeabil-ity, gloss, corrosion, surface electrostatic charging, cellular recognition, and biocompatibility. Interfacial characteristics of polymer systems control the domain size and the stability of polymer-polymer dispersions, adhesive strength of laminates and composites, cohesive strength of polymer blends, mechanical properties of adhesive joints, etc. 

In recent years, we have extended the nature of our analysis to include certain statistically defined features of the surface electrostatic potential. Our purpose has been to expand the capabilities of V(r) for quantitatively describing macroscopic properties that reflect non-covalent molecular interactions. This has led to the development of the General Interaction Properties Function (GIPF), described by Eq. (3.7) ... 

Murray, J. S., T. Brinck, and P. Politzer. 1996. Relationships of Molecular Surface Electrostatic Potentials to Some Macroscopic Properties. Chem. Phys. 204, 289. 

In summary, the removal of organic matter and Fe oxides significantly changes the physicochemical and surface chemical properties of soils. Thus, this pretreatment affects the overall reactivity of heavy metals in soils. The removal of organic matter and Fe oxides may either increase or decrease heavy metal adsorption. The mechanisms responsible for the changes in metal adsorption in soils with the removal of organic matter and Fe oxides include increases in pH, surface area, CEC and electrostatic attraction, decreases in the ZPC, shifts of positive zeta potentials toward... 

MolSurf parameters [33] are descriptors derived from quantum mechanical calculations. These descriptors are computed at a surface of constant electron density, with which a very fine description of the properties of a molecule at the Van der Waals surface can be obtained. They describe various electrostatic properties such as hydrogen-bonding strengths and polarizability, as well as Lewis base and acid strengths. MolSurf parameters are computed using the following protocol. 

Statistical Characterization of the Molecular Surface Electrostatic Potential - the General Interaction Properties Function (GIPF)... 

At oxide surfaces, the surface activities of H+ and OH are not fixed in a similar way. Then the variation in surface potential with solution activity of H+ depends on the chemical and electrostatic properties of the interface. For the many oxides that are insulators, it is much more difficult to obtain a measurement of the surface-solution potential differences than it is for conductors such as Agl. Thus there is uncertainty whether the dependence of surface potential on pH is approximately Nernstian or significantly sub-Nernstian. 

When the electrostatic properties are evaluated by AF summation, the effect of the spherical-atom molecule must be evaluated separately. According to electrostatic theory, on the surface of any spherical charge distribution, the distribution acts as if concentrated at its center. Thus, outside the spherical-atom molecule s density, the potential due to this density is zero. At a point inside the distribution the nuclei are incompletely screened, and the potential will be repulsive, that is, positive. Since the spherical atom potential converges rapidly, it can be evaluated in real space, while the deformation potential A(r) is evaluated in reciprocal space. When the promolecule density, rather than the superposition of rc-modified non-neutral spherical-atom densities advocated by Hansen (1993), is evaluated in direct space, the pertinent expressions are given by (Destro et al. 1989)... 

In systems containing two or more adsorbates, either competitive or synergistic effects may operate. The commonest synergistic effect is that of ternary adsorption (11.5.4). Competitive behaviour may involve competition for the same surface sites, indirect effects due to the change in the electrostatic properties of the oxide/water interface and in some cases, formation of non sorbing, metal-ligand complexes in solution. 

Property Map. A representation or map of a property on top of an Isosurface, typically an Isodensity Surface. Electrostatic Potential Maps, and HOMO and LUMO Maps and Spin Density Maps are useful property maps. 

An additional microbial surface property that is of critical importance to successful bioremediation of subsurface pollution is transport through soil. Studies on the movement of bacteria through soil with moving water indicated that several properties are involved (Gannon, Manilal Alexander, 1991), including cell size, hydrophobicity, and net surface electrostatic charge. 

Murray, J. S., et al., Statistically-Based Interaction Indices Derived from Molecular Surface Electrostatic Potentials A General Interaction Properties Function (GIPF). J. Mol. Struct. (Theochem.), 1994 307, 55—64. 

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