Sedimentation potential techniques

Surface Charge Characteristics of Blood Cells Using Mainly Electrophoresis and to a Limited Extent Sedimentation Potential Techniques... 

The second technique, known as electro-osmosis, causes a fluid in contact with a stationary charged surface to move in response to an applied electric field. The third technique, which can be regarded as the converse of electro-osmosis, is known as the streaming potential technique. The streaming potential involves the measurement of the electric potential generated when a liquid is forced under pressure to move in contact with a stationary charged surface. Finally, the sedimentation potential technique is a method that is, in a way, the converse of electrophoresis. A sedimentation potential arises across the suspension when charged particles settle in a stationary liquid. Adamson (29) explained the basic principles of these electrokinetic techniques in a nutshell as shown in Table 2. 

The 2eta potential (Fig. 8) is essentially the potential that can be measured at the surface of shear that forms if the sohd was to be moved relative to the surrounding ionic medium. Techniques for the measurement of the 2eta potentials of particles of various si2es are collectively known as electrokinetic potential measurement methods and include microelectrophoresis, streaming potential, sedimentation potential, and electro osmosis (19). A numerical value for 2eta potential from microelectrophoresis can be obtained to a first approximation from equation 2, where Tf = viscosity of the liquid, e = dielectric constant of the medium within the electrical double layer, = electrophoretic velocity, and E = electric field. 

Good descriptions of practical experimental techniques in conventional electrophoresis can be found in Refs. [81,253,259]. For the most part, these techniques are applied to suspensions and emulsions, rather than foams. Even for foams, an indirect way to obtain information about the potential at foam lamella interfaces is by bubble electrophoresis. In bubble microelectrophoresis the dispersed bubbles are viewed under a microscope and their electrophoretic velocity is measured taking the horizontal component of motion, since bubbles rapidly float upwards in the electrophoresis cells [260,261]. A variation on this technique is the spinning cylinder method, in which a bubble is held in a cylindrical cell that is spinning about its long axis (see [262] and p.163 in Ref. [44]). Other electrokinetic techniques, such as the measurement of sedimentation potential [263] have also been used. 

The measurements of buoyant bubble velocity is not suitable for solving these problems and attention must be paid to other experimental techniques, li is clear that investigations of surfactant transfer in foams and of sedimentation potential measurements deserve more attention. 

Electrokinetic Phenomena. Electrokinetic motion occurs when the mobile part of the EDL is sheared away from the inner layer (charged surface). There are four types of electrokinetic measurements, electrophoresis, electroosmosis, streaming potential, and sedimentation potential, of which the first finds the most use in industrial practice. Good descriptions of practical experimental techniques in electrophoresis and their limitations can be found in references 18-20. 

The potential may be obtained from measurements of particle mobility using electrokinetic techniques, such as electrophoresis or sedimentation potential [70]. Electrophoresis, the standard technique for submicrometer particles, is based on the movement of charged particles in response to an applied electrical field. Optical scattering methods are used to measure the distribution of particle velocities for a given field strength, and may then be calculated using the Henry equation. 

The zeta potential of a particle is calculated from electro kinetic phenomena such as electrophoresis, streaming potential, electro-osmosis and sedimentation potential. Each of these phenomena and the determination of zeta potential by using each technique will be discussed briefly in this section. 

Sedimentation potential This is the creation of an electric field when charged particles move relative to a stationary fluid. This technique is the least commonly used for the determination of zeta potential, because of several limitations associated with the measurement and calculation of the zeta potential. 

Of these four, the phenomenon of greatest practical interest is electrophoresis. Over the years, several relatively easy techniques for the study and application of electrophoresis have been developed and today these are important tools in many areas of science and technology, including colloid science, polymer science, biology, and medicine. Of lesser practical importance, and less intensely studied, are electroosmosis and streaming potential. Sedimentation potential has received relatively little attention because of experimental difficulties. 

Several techniques can be used to separate phenol. Solvent extraction using gas oil or lube oil (process MSAs Sj and S2, respectively) is a potential option. Besides the purification of wastewater, the transfer of phenol to gas oil and lube oil is a useful process for the oils. Phenol tends to act as an oxidation inhibitor and serves to improve color stability and reduce sediment formation. The data for the waste streams and the process MSAs are given in Tables 3.4 and 3.5, respectively. 

Suspensions are generally evaluated with respect to their particle size, electrokinetic properties (zeta potential), and rheological characteristics. A detailed discussion on the methods/techniques and relevant instrumentation is given in Sec. VII. A number of evaluating methods done specifically with suspension dosage forms, such as sedimentation volume, redispersibility, and specific gravity measurements, will be treated in this section. 

Polychlorinated biphenyls (PCBs) were manufactured by catalytic chlorination of biphenyl to produce complex mixtures, each containing 60-90 different PCB molecular species or congeners (see Chaps. 1 and 4). In the United States, PCB mixtures were manufactured by Monsanto under the trade name Aroclor and were widely used as dielectric fluids in capacitors and transformers from 1929 to 1978. PCBs are widespread contaminants of aquatic sediments and continue to be a focus of environmental concern because they tend to accumulate in biota and are potentially toxic. The following sections show the most effective bioremediation techniques applied to various PCB contaminated environments ... 

In some cases, when petroleum and/or petroleum products are released to the environment, a free phase is formed and sample(s) of the hydrocarbon material can be collected directly for characterization. The ability to analyze free product greatly aids the determination of product type and potential source. The samples may be diluted prior to analysis EPA SW-846 3580 (waste dilution) gives some guidelines for proper dilution techniques. However, caution is advised since as part of the initial sample collection procedure, water and sediment may be included in the sample inadvertently. Several protocols involved in initial isolation and cleanup of the sample must be recognized. In fact, considerable importance attaches to the presence of water or sediment in crude oil (ASTM D1796, D4007), for they lead to difficulties in other analyses. 

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