Electrokinetic effects sedimentation potential

There are four related electrokinetic phenomena which are generally defined as follows electrophoresis—the movement of a charged surface (i.e., suspended particle) relative to astationaiy hquid induced by an applied ectrical field, sedimentation potential— the electric field which is crested when charged particles move relative to a stationary hquid, electroosmosis—the movement of a liquid relative to a stationaiy charged surface (i.e., capiUaty wall), and streaming potential—the electric field which is created when liquid is made to flow relative to a stationary charged surface. The effects summarized by Eq. (22-26) form the basis of these electrokinetic phenomena. 

If a liquid moves tangential to a charged surface, then so-called electrokinetic phenomena arise [101]. Electrokinetic phenomena can be divided into four categories Electrophoresis, electro-osmosis, streaming potential, and sedimentation potential [102], In all these phenomena the zeta potential plays a crucial role. The classic theory of electrokinetic effects was proposed by Smoluchowski2 [103],... 

In classical electrokinetic phenomena, the forces and fluxes are independent of time. Electroacoustic effects are analogs of electrophoresis and sedimentation potential in which the forces and fluxes are variable in time. Alternating forces induce alternating fluxes of the same frequency, with a time delay. The phenomenological coefficients between the force and coupled flux can be used to calculate the potential. The phase shift is a source of additional information about the system. The electric sonic amplitude (ESA) is the amplitude of the ultrasonic field... 

Systematic studies of bubble hydrodynamics based on the Dom effect were suggested by Dukhin (1983). A comprehensive study, comprising the measurement of adsorption on immobile surfaces with the calculation of the Stem potential and measurements of sedimentation potentials, should be performed with homologous series of ionic surfactant so that the condition (8.97) is fulfilled by higher homologues and the opposite condition (8.101) by the lower ones. With decreasing surface activity the condition (8.97) will be fulfilled at smaller adsorption values. This means that the lower the surface activity, the smaller should be the deviation of the electrokinetic potential from the Stem potential at respective values of adsorption. And finally, when condition (8.97) is not fulfilled the electrokinetic and Stem potentials must coincide over the whole concentration interval. 

The term electrokinetic is applied to a group of effects in which either an electric potential brings about movement, or movement produces an electric potential. For example, if macromolecuies are suspended in a liquid, and a potential is applied, the particles often move towards one or other of the electrodes. This phenomenon is called electrophoresis. The inverse of it is when the particles undergo sedimentation, in which case a sedimentation potential is developed. The occurrence of these electrokinetic effects is due to the existence of potential differences between the solid and liquid phases. 

There are two types of electrokinetic phenomena, namely those in which an electric potential is generated by the mechanical notion of a surface in a liquid and those in which a particle or liquid is caused to move by an electric potential. Classically there are four major effects, i.e., streaming potentials, sedimentation potentials, electrophoresis, and electroosmosis. (There are also several secondary effects that have been noted more recently such as acoustic potentials,K effect potentials, and U effect potentials.Each of the major effects has found a niche in physical chemistry, analytical chemistry, and chemical engineering. However, the application and understanding of electrokinetic phenomena in the biological sciences has been very spotty. 

The classic experimental approach when measuring electrokinetic phenomena is to measure either the velocity of the respective phases, in the case of electrophoresis and electroosmosis, or the strength of the induced electric field under relative phase motion, in the case of streaming potential and sedimentation potential. A number of experimental set-ups can be used to measure electrokinetic phenomena. However, the appropriate experimental set-up for a given system is usually determined by the size, shape and state of the substrate of interest. The following provides a discussion of some common experimental regimes for measurement of electrokinetic effects. 

The four possible types of electrokinetic phenomena are streaming (current) potential (electric potential generated by fluid movement relative to another phase), sedimentation potential or Dorn phenomenon or Dom effect (due to dispersed particles motion relative to the fluid caused by sedimentation) and electrophoresis and electro-osmosis (movement of two phases is caused by an external potential difference). 

Two other electrokinetic effects result from the flow of liquid past a stationary charge. In electro-osmosis, the flow of Uquid past a stationary charged surface (for example the wall of a capillary tube) is induced by an applied electric field. The pressure necessary to counterbalance this flow is called the electro-osmotic pressure. In the reverse effect, the electric field generated by charged particles flowing relative to a stationary liquid is termed the sedimentation potential. 

The electroviscous effects are observed as variations of viscosity upon appHcation of outer electric fields, and as build-up of potential gradients upon flow of such fluids. See also electroconvection, electrorheological fluid, -> sedimentation potential, electrokinetic effect, -> electroendosmotic flow. 

The most popular and straightforward way to determine zeta potential is to apply an electric field to a colloidal suspension. In the case of neutral particles nothing happens, while particles carrying surface charges will have an oriented motion dependent on the direction of the electric field. Several phenomena (collectively known as electrokinetic effects) are observed i.e., electrophoresis, electroosmosis, streaming potential, and sedimentation potential. In this chapter we will discuss the first two effects. 

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