Laser Doppler electrophoresis

In most experiments the smallest amount of electrolyte needed to coagulate the sols measured after 2 hours standing was chosen as the CCC. When using HC1, this point is the critical coagulation pH. A constant temperature water bath was used for temperature different than 23°C. The pH values were measured with a Beckman Model 96A pH meter and a Fisher combination electrode. The electrophoretic mobility measurements were made with a Laser Doppler Electrophoresis apparatus. These experiments were performed by Mr. J. Klein of the Chemistry Department, Syracuse University. 

Dalgleish, D.G. 1984. Measurement of electrophoretic mobilities and zeta-potentials of particles from milk using laser Doppler electrophoresis. J. Dairy Res. 51, 425 138. 

There are two commonly applied ELS experimental methods laser Doppler electrophoresis (LDE) [ 111, a subset of laser Doppler velocimetry (LDV) [37,50.138]. 

The application of laser Doppler velocimetry (LDV) to measure the electrophoretic mobility n of charged colloidal particles is known as laser Doppler electrophoresis (LDE). In a typical LDE experiment, an applied electric field drives the collective motion of charged colloidal particles. The particles pass through an interference pattern created by a dual-beam experimental setup (Section III.A.2). The collective electrophoretic velocity of the particles is then determined via intensity- or spectrum-based analysis of the scattered light, and the electrophoretic mobility n is calculated by dividing the velocity by the applied electric field strength. 

The term microelectrophoresis, or even better, microscopic electrophoresis, refers to a technique in which the motion of individual particles is followed, usually ultramicroscoplcally. Other terms refer to alternative ways of measurement, such as moving boundary electrophoresis, paper electrophoresis, laser-Doppler electrophoresis, gel electrophoresis, capillary electrophoresis, etc. see secs. 4.5 and 10. 

Miller, J.D.. Yalamanchili. M.R.. and Kellar, J.J.. Surface charge of alkali halide paticles as determined by laser-Doppler electrophoresis. Lanr muir, 8, 1464, 1992. 

This is a recent method which derives from the development of laser techniques [22,23]. It consists in the use of a double laser Doppler electrophoresis apparatus to determine bubble electrophoretic mobility by measurement of the difference in the bubble-rise rates, with and without an electric field. The latter is applied parallel to the bubble-rise vector, causing either a decrease or an increase in the natural rise rates of the bubbles according to its direction. 

Sample heating and electrode polarization are greatly reduced in laser-Doppler electrophoresis instruments due to certain features incorporated in the technique. These features facilitate electrophoretic measurements even in solutions with high salt concentrations. 

The nonequilibrium electrophoretic mobilities of selected alkali halides were measured during dissolution hy laser-Doppler electrophoresis. As stated, the measurements were made during a time interval of 10-15 s. The results were found to be quite reproducible with respect to the sign of the electrophoretic mobility. 

It should be mentioned that diffusiophoresis, the movement of particles in suspension under the influence of an externally imposed solution concentration gradient, can affect the nonequilibrium measurements of alkali halide particles. When a particle of an alkali halide salt is dissolving in solution, it is possible that a concentration gradient will be established in the volume adjacent to the outer boundary of the double layer. The concentration gradient thus established can influence the measured electrophoretic mobilities by laser-Doppler electrophoresis. However, in the case of alkali halide particles, the slope of the concentration... 

Electrophoretic mobility measurements by laser-Doppler electrophoresis. Source Ref 7. 

Phase analysis light scattering (PALS) is a technique that is very similar to laser Doppler electrophoresis (LDE) and is used to measure the electrophoretic mobilities of colloidal particles. This technique is particularly suited to measurements of charged particles suspended in nonpolar media and sensitivity of the method is far superior to that which could be obtained by LDE measurements. It makes use of a cross-beam technique and offsets one of the laser beams relative to the other by several kEIz. ... 

Smith, B. A., Ware, B. R., Apparatus and Methods for Laser Doppler Electrophoresis, in Contemporary Topics in Analytical and Clinical Chemistry v.2, Eds. Hercules, D., Hieftje, M., Snyder, L. R., Evenson, M. A., Plenum, New York, 1978, Chpt. 2, p29-54. 

Electrokinehc measurements [20] are used to access the electrophoretic mobility /tg of the polymer particles and thereby to get information on their charges. Because of the relahvely small parhcle size of 100 to 250 nm, the measurement technique used for polymer dispersions is laser Doppler electrophoresis. Sample preparation and experimental set-up correspond to those of a dynamic light scattering experiment (Sect 3.2.2, Fig. 3-6). The only difference is a pair of electrodes immersed in the sample between which the particles are moved backwards and forwards by an al-ternahng voltage. 

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