Electrophoretic effect mobility

Electron spin resonance. 353 Electrophoretic mobility effect of ionic strength on, 242 effect of particle size on, 247 EMF method, 84 Enthalpy of adsorption, 318-320 at constant cto, 320 EpHL method, 82 Equiadsorption point, 73 Equilibrium constant, 52, 588 Ethers, surface charging in the presence of, 10... 

Figure 5.9. Electrophoretic mobility effects of (a) bone and (b) pig gelatins adsorbed on cubic AgBr, glass beads and polyethylene at 24°C. Reproduced by permis.sion from J.I. Cohen, W.L. Gardner and A.H. Herz, Advances in Chemistry Series, 145, 198-217 (1975) 1975 by The American Chemical Society...

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]. 

These effects can be illustrated more quantitatively. The drop in the magnitude of the potential of mica with increasing salt is illustrated in Fig. V-7 here yp is reduced in the immobile layer by ion adsorption and specific ion effects are evident. In Fig. V-8, the pH is potential determining and alters the electrophoretic mobility. Carbon blacks are industrially important materials having various acid-base surface impurities depending on their source and heat treatment. 

Surface active electrolytes produce charged micelles whose effective charge can be measured by electrophoretic mobility [117,156]. The net charge is lower than the degree of aggregation, however, since some of the counterions remain associated with the micelle, presumably as part of a Stem layer (see Section V-3) [157]. Combination of self-diffusion with electrophoretic mobility measurements indicates that a typical micelle of a univalent surfactant contains about 1(X) monomer units and carries a net charge of 50-70. Additional colloidal characterization techniques are applicable to micelles such as ultrafiltration [158]. 

Overbeek and Booth [284] have extended the Henry model to include the effects of double-layer distortion by the relaxation effect. Since the double-layer charge is opposite to the particle charge, the fluid in the layer tends to move in the direction opposite to the particle. This distorts the symmetry of the flow and concentration profiles around the particle. Diffusion and electrical conductance tend to restore this symmetry however, it takes time for this to occur. This is known as the relaxation effect. The relaxation effect is not significant for zeta-potentials of less than 25 mV i.e., the Overbeek and Booth equations reduce to the Henry equation for zeta-potentials less than 25 mV [284]. For an electrophoretic mobility of approximately 10 X 10 " cm A -sec, the corresponding zeta potential is 20 mV at 25°C. Mobilities of up to 20 X 10 " cmW-s, i.e., zeta-potentials of 40 mV, are not uncommon for proteins at temperatures of 20-30°C, and thus relaxation may be important for some proteins. 

Gorin has extended this analysis to include (1) the effects of the finite size of the counterions in the double layer of spherical particles [137], and (2) the effects of geometry, i.e. for cylindrical particles [2]. The former is known as the Debye-Huckel-Henry-Gorin (DHHG) model. Stigter and coworkers [348,369-374] considered the electrophoretic mobility of polyelectrolytes with applications to the determination of the mobility of nucleic acids. 

The tortuous-path and barrier theories consider the effects of the media on the electrophoretic mobility in a way similar to the effect of media on diffusion coefficients discussed in a previous section of this chapter. The tortuons-path theory seeks to determine the effect of increased path length on electrophoretic mobility. The barrier theory considers the effects of the barrier or media conductivity on the electrophoretic mobility. 

FIG. 28 Effective electrophoretic mobility in the case of hindered diffusion. (Reproduced with permission from Ref. 399.)... 

Determination of the effective transport coefficients, i.e., dispersion coefficient and electrophoretic mobility, as functions of the geometry of the unit cell requires an analogous averaging of the species continuity equation. Locke [215] showed that for this case the closure problem is given by the following local problems ... 

The standard Rodbard-Ogston-Morris-Killander [326,327] model of electrophoresis which assumes that u alua = D nlDa is obtained only for special circumstances. See also Locke and Trinh [219] for further discussion of this relationship. With low electric fields the effective mobility equals the volume fraction. However, the dispersion coefficient reduces to the effective diffusion coefficient, as determined by Ryan et al. [337], which reduces to the volume fraction at low gel concentration but is not, in general, equal to the porosity for high gel concentrations. If no electrophoresis occurs, i.e., and Mp equal zero, the results reduce to the analysis of Nozad [264]. If the electrophoretic mobility is assumed to be much larger than the diffusion coefficients, the results reduce to that given by Locke and Carbonell [218]. 

The electrophoretic mobilities of flexible macromolecnles (e.g., DNA, oligonucleotides, and other polymers) in gel media have also been extensively stndied by a nnm-ber of methods, including Monte Carlo simnlations [159,165,208,357,358,361,362,447]. In general, the mobility is expected to vary with the length of the polymer to the -1 power (p N y, however, there are complicating effects of the applied electric field as well as the... 

Ta = absolute temperature u = electrophoretic mobility Meff = effective electrophoretic mobility... 

Ohshima, H Kondo, T, Electrophoretic Mobility and Donnan Potential of a Large Colloidal Particle with a Surface Charge Layer, Journal of Colloid and Interface Science 116, 305, 1987. O Neil, GA Torkelson, JM, Modeling Insight into the Diffusion-Limited Cause of the Gel Effect in Free Radical Polymerization, Macromolecules 32,411, 1999. 

Davies, R. and Prcece, A.W. (1983). The electrophoretic mobilities of minerals determined by laser Doppler velocimetry and their relationship with the biological effects of dusts towards macrophages. Clin. Phys. Physiol. Meas. 4, 129-140,... 

Williams, B. A. and Vigh, G., Effect of the initial potential ramp on the accuracy of electrophoretic mobilities in capillary electrophoresis, Anal. Chem., 67, 3079, 1995. 

A second possibility is that the Au particles scavenge electrons from the reaction electrodes, walls and solvent. This is the explanation we favor at the present time since we have been able to effect changes in electrophoretic mobilities by supplying electrical potential to the colloid solution as the particles form,( l ) and the fact that such charging has been reported before, for example with oil droplets in water.(43)... 

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