Zeta Electrokinetic Potential

The concept of the zeta potential,, is one of the most significant concepts in the sdence of colloidal processing of days and ceramics. The functional dependency of this property on the type and concentration of ions, including pH, in the suspension serves to characterize the suitability of days for a variety of ceramic wares. 

Historically, the electrical double layer concept has been proposed by Helmholtz (1879). According to this theory, two rigid layers of positive and negative ions exist close to the particle surface with a linear decay in potential, akin to an electric capacitor [U = 4n-Q-d)jA, where U is the potential, Q the electric charge, d the 

Since I is a function of the concentration of all ions q in solution and their valencies Zj, it follows that  

Maximizing I involves a low concentration of large monovalent ions. In this case, the zeta potential will also be large, and the colloidal solution will be stabihzed against coUapse and flocculation. Typical values of L for a NaCl solution are 30 nm at lO molT, and Inm at 0.1 moll . Similarly for an MgS04 solution, L = 15nm at lO molT and 0.5nm at 0.1 molT . 

Another quantitative expression of the zeta potential is based on the assumption of the vaUdily of the Helmholtz approach of the electrical double layer behaving 

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EUmelech M., Chen W.H., Waypa J.J. (1994), Measuring the zeta (electrokinetic) potential of reverse osmosis membranes by a streaming potential analyzer, Desalination, 95, 269-286. 

I = zeta (electrokinetic) potential De = dielectric constant of the medium ri = viscosity of the medium d/dx — potential gradient... 

As the particle moves relative to the electrolyte solution, the layer of water mol-ecnles that is directly adjacent to the particle surface is strongly bonnd and will be pnlled along. The thickness of this bonnd layer is approximately one or two diameters of a water molecule. We shall write x, for the x-coordinate of this layer s outer boundary, which is the slip plane. The electrostatic potential at this plane relative to the potential in the bulk solution is designated by the Greek letter and called the zeta potential or electrokinetic potential of the interface discussed. This potential is a very important parameter characterizing the electrokinetic processes in this system. 

The potential governing these electrokinetic effects is clearly at the boundary (the face of shear) between the stationary phase (the fixed double layer) and the moving phase (the solution). This potential is called the electrokinetic potential or the zeta potential. An electrokinetic phenomenon in soil involves coupling between electrical, chemical, and hydraulic gradients. 

The electrokinetic potential (zeta potential, Q is the potential drop across the mobile part of the double layer (Fig. 3.2c) that is responsible for electrokinetic phenomena, for example, elecrophoresis (= motion of colloidal particles in an electric field). It is assumed that the liquid adhering to the solid (particle) surface and the mobile liquid are separated by a shear plane (slipping plane). The electrokinetic charge is the charge on the shear plane. 

In each case the electrokinetic measurements can be interpreted to yield a quantity known as the zeta (f) potential. It is important to note that this is an experimentally determined potential measured in the double layer near the charged surface. Therefore it is the empirical equivalent... 

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. 

These authors also defined a shear plane, not necessarily coincident with the outer Helmholtz plane, which is extremely important in electrokinetic effects (Section 3.7). The shear plane limits the zone where the rigid holding of ions owing to the electrode charge ceases to operate. The potential of this plane is called the zeta or electrokinetic potential, f. 

One can attribute the relative stability of colloids, or dispersed particles, to a theoretical electrokinetic potential, or zeta potential, or potential, which is defined as the potential difference between the bulk solvent and a very thin layer of the solvent (called the "slipping plane" and typically about lnm thick) that is tightly attached to the colloidal particle or nanoparticle. This potential cannot be measured directly, but... 

Electrokinetic phenomena electrokinetic effects Electrokinetic potential -> zeta potential Electrokinetic remediation -> electroremediation... 

Zeta potential — The electrical -> potential difference between the bulk solution and the shear plane or outer limit of the rigid part of the double layer (the limits of the diffuse - double layer) is the electrokinetic potential , often called the Zeta potential ((or more precisely the Zeta potential difference (). 

Fig. 3.25 presents the aqueous solutions in the absence of a surfactant at constant ionic strength (HC1 + KC1) [186,197], It can be seen that at pH > 5.5, op-potential becomes constant and equal to about 30 mV. At pH < 5.5 the potential sharply decreases and becomes zero at pH 4.5, i.e. an isoelectric state at the solution surface is reached. As it is known, the isoelectric point corresponds to a pH value at which the electrokinetic phenomena are not observed. Since in the absence of the potential of the diffuse electric layer, the electrokinetic potential (zeta-potential) should also be equal to zero, the isoelectric point can be used to determine pH value at which isoelectric state is controlled by the change in pH. This is very interesting, for it means that the charge at the surface of the aqueous solutions is mainly due to the adsorption of H+ and OH" ions. Estimation of the adsorption potential of these ions in the Stem layer (under the assumption that the amounts of both ions absorbed are equal) showed that the adsorption potential of OH" ions is higher. It follows that ( -potential at the solution/air interface appears as a result of adsorption of OH" ions. 

Zeta Potential Properly called the electrokinetic potential, the zeta potential refers to the potential drop across the mobile part of the electric double layer. Any species undergoing electrophoretic motion moves with a certain immobile part of the electric double layer that is assumed to be distinguished from the mobile part by a sharp plane, the shear plane. The zeta potential is the potential at that plane. 

The kinetic potential is usually denoted as the zeta (0 potential and it is determined from the electrophoretic mobility of the extremely dilute particles in an electric field. More recently, the nse of electrokinetic sonic amplitude (ESA), acoustosizer (AZR), or colloid (or ultrasonic) vibration potential (CVP) has become available for the determination of the potential in rather concentrated particle suspensions. Again the potential may be measured as a function of either the metal concentration or the pH. In the latter case the point where the mobility ceases is denoted the isoelectric point (pH,Ep Fignre 8.27). It correlates particnlarly well with the stability of the sol. 

Zeta potential It relates to the electrokinetic potential across the interface of all solids and liquids and specifically to that of the diffuse layer of ions surrounding a charged colloidal particle. Such a diffuse aggregation of positive and negative electric charges surrounding a suspended colloidal particle is largely responsible for colloidal stability. 

Starting with the basic concept of the electrokinetic potential of colloidal particles, the so-called zeta potential, i.e., the electrokinetic potential at the shear plane, the most important well-established methods of zeta potential determination are discussed separately. Taking into account the peculiarities of kaolin particles, the relevance of these methods for characterizing kaolin particles in the absence and the presence of polyelectrolytes are outlined here. Thereby a mixed stabilization by oppositely charged polyelectrolytes is discussed in more detail. 

Electrokinetic potential of the alumina samples redispersed in 0.001 N KNO3 was measured over a pH range between 2 and 9.5 with a Pen Chem System 300 instrument. The coated alumina powder was ultrasonically dispersed at 0.001 wt% into 300 mL of 0.001 N KNO3 for ca. 15 min and immediately placed under N2 atmosphere. A 50-mL portion was placed onto a titration stirrer under N2 atmosphere that was fitted with a pH probe, a mechanical stirrer, and a port for addition of titrant. A portion of sample was pumped into the S3000 cell, which was fitted into a constant temperature bath set at 25 °C. This sample portion was used to rinse the cell of the previous sample. A second portion of sample was pumped into the cell. The pH was recorded and the zeta potential was measured. Two measurements were taken, one at the front stationary layer and the second at the back stationary layer. The histograms were then combined and averaged. The pH was adjusted with either 0.01 N KOH or 0.01 N HNO3, and measurements were repeated for each desired pH value. Once all the desired pH versus zeta potential data were obtained, the data were transferred to an IBM PC and plotted. Estimates of isoelectric points (IEPs) were made from the plots obtained. 

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