Zeta potential media

Fig. 8. Electrical double layer of a sohd particle and placement of the plane of shear and 2eta potential. = Wall potential, = Stern potential (potential at the plane formed by joining the centers of ions of closest approach to the sohd wall), ] = zeta potential (potential at the shearing surface or plane when the particle and surrounding Hquid move against one another). The particle and surrounding ionic medium satisfy the principle of electroneutrafity.

R = factor for electrical relaxation D = dielectric constant of medium F = factor for size of spheres and = zeta potential. 

This equation is a reasonable model of electrokinetic behavior, although for theoretical studies many possible corrections must be considered. Correction must always be made for electrokinetic effects at the wall of the cell, since this wall also carries a double layer. There are corrections for the motion of solvated ions through the medium, surface and bulk conductivity of the particles, nonspherical shape of the particles, etc. The parameter zeta, determined by measuring the particle velocity and substituting in the above equation, is a measure of the potential at the so-called surface of shear, ie, the surface dividing the moving particle and its adherent layer of solution from the stationary bulk of the solution. This surface of shear ties at an indeterrninate distance from the tme particle surface. Thus, the measured zeta potential can be related only semiquantitatively to the curves of Figure 3. 

The zeta potential is a measurable indication of the apparent particle charge in the dispersion medium. When its value is relatively high, the repulsive forces usually exceed the attractive forces. Accordingly, the particles are individually dispersed and are said to be deflocculated. Thus, each particle settles separately, and the rate of sedimentation is relatively small. The settling particles have plenty of time to pack tightly by falling over one another to form an impacted bed. The sedimentation volume of such a system is low, and the sediment is difficult to redisperse. The supernatant remains cloudy even when settling is apparent. 

Zeta potential The potential existing between the suspending medium and the effective electrical surface of a particle. 

As is derived from Equation (8), can be adjusted by changing the dielectric constant and/or the viscosity of the medium, but also C- As mentioned before, the zeta potential is mainly influenced by the distribution of charges at the capillary wall. All alterations resulting in a change of the charge distribution at the capillary wall like changes in the pH, ionic strength, valence of ions in the buffer electrolyte, etc., can be applied to adjust the velocity of the EOF. 

The zeta potential is the difference in potential between that of the total dispersed system and that of the layer at the interface of the dispersed particles (in this case cement) and the dispersing medium (water). Many studies have been made of the effect of superplasticizers on the zeta potential of the cement-water system from which the following conclusions can be drawn ... 

Kamo et al. [Biochim. Biophys. Acta, 367, 1 and 11 (1974)] have shown that nonionic sugars modify the zeta potential of slime mold cells. Aggregation of colloids is related to their surface charge and their surface potential. This fact shows evidence of long-range electrostatic interactions controlled by metabolic reactions taking place at the membrane and able to modify the composition of the membrane medium interface. In this process the diffusion is not relevant, as indicated by Mrs. Babloyantz. 

Table 7.2 Effect of the presence of an anionic polysaccharide on the measured zeta potential (Q of emulsion droplets stabilized by proteins under experimental conditions corresponding to protein-polysaccharide complexation. In all cases the complexes were formed in the bulk aqueous medium before emulsification.

The distribution of ions in the diffuse part of the double layer gives rise to a conductivity in this region which is in excess of that in the bulk electrolyte medium. Surface conductance will affect the distribution of electric field near to the surface of a charged particle and so influence its electrokinetic behaviour. The effect of surface conductance on electrophoretic behaviour can be neglected when ka is small, since the applied electric field is hardly affected by the particle in any case. When tea is not small, calculated zeta potentials may be significantly low, on account of surface conductance. 

Electro-osmosis is a direct consequence of the existence of zeta potential between the sol particles and the medium. When the applied potential exceeds the zeta potential, the diffused layer moves and causes electro-osmosis. 

The presence of charges of opposite signs on the fixed and diffuse parts of the double layer produces a potential between the two layers. This potential is known as electrokinetic potential or zeta potential. It is represented by (zeta). It is therefore the electromotive force which is developed between the fixed layer and the dispersion medium. 

The ionic strength of the mobile phase can influence both the zeta potential of the column and the viscosity of the medium. Theory predicts that increasing the... 

Drug-loaded nanoparticles were also evaluated for their safety and efficacy. Paclitaxel-encapsulated 6-O-CAPRO-p-CD nanospheres and nanocapsules were evaluated for their physical stability in a one-month period in aqueous dispersion form with repeated particle size and zeta potential measurements and AFM imaging to evaluate recrystallization in aqueous medium. Paclitaxel-loaded amphiphilic CD nanoparticles were found to be physically stable for a period of one month whereas recrystallization occurs within minutes when diluted for intravenous (IV) infusion [85], Finally, paclitaxel-loaded amphiphilic nanoparticles were demonstrated to show similar anticancer efficacy against MCF-7 cells when compared to paclitaxel solution in a cremophor vehicle [85],... 

When charged particles settle in an aqueous solution, an electric field is induced by the movement of the charged particles relative to the ionic medium, as discussed in Chapter 9. A formula relating the electric field, E (= volts/cm), to the zeta potential, of the particles... 

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