Quartz, electrophoretic mobility

The adsorption of Co(II) at the silica-water interface has been studied as a function of pH, ionic strength, and total Co(II) concentration. The adsorption data, together with electrophoretic mobility and coagulation data suggest that the free aquo Co(II) ion is not specifically adsorbed without participation of surface hydroxyls. Evidence for polymeric Co(OH)2 at the quartz surface is presented together with evidence of mutual coagulation of the quartz and precipitated cobalt hydroxide. 

Figure 1. The coagulation and electrophoretic mobility (microns sec. 1 /volt cm. 1) behavior of quartz in electrolyte solutions as a function of pH...

Electrophoretic mobilities of the quartz particles in cobalt (II) perchlorate solutions were determined with a calibrated Zeta-Meter apparatus. Coagulation sedimentation behavior was followed using a stop-flow type apparatus. The dispersion is pumped in a closed loop from an equilibration vessel through an optical cell located in the sample compartment of a recording spectrophotometer. From the optical densitytime curve obtained from the time the pump is switched off, the turbidity index (in arbitrary units) is obtained as the slope of the curve at zero time. 

The variation with pH of the electrophoretic mobility of quartz in 10"4M cobalt (II) perchlorate and a comparison of the mobility of quartz in 10 4M KC1 is shown in Figure 5. Included in Figure 5 is the variation with pH of electrophoretic mobility of precipitated cobalt (II) hydroxide. It can be seen that the silica surface with adsorbed Co (II) acts as cobalt (II) hydroxide for pH values above 8.0. The turbidity vs. pH behavior at 10 4M Co(C104)2 is shown in Figure 6. The two curves represent the behavior for increasing and decreasing pH and within experimental error the curves superimpose. 

The glass fibers and fused-silica glass (Thermal American Fused Quartz Co.) were crushed and then dispersed in water. The pH of this near-neutral suspension was varied using KOH or HNO,. In some experiments, a hydrolyzed solution of y-APS was added to this suspension. Here, the initial pH was 10. The electrophoretic mobilities of glass fragments suspended in these solutions were measured without any further treatment except for the addition of electrolyte (10-3 M KNO,). These analyses were performed using a Rank Brothers Particle Micro-Electrophoresis Apparatus Mark II or a Pen Kem System 3000 Automated Electrokinetics Analyzer. 

The electrophoretic mobilities of small colloidal particles, as well as of larger quartz particles, oil drops and air bubbles, are always about 2 to 4 X 10 cm. per sec. in water hence, in accordance with the requirements of equation (25), rj being 0.01 e.g.s. unit (poise) and D approximately 80, the value of the zeta-potential is between 0.03 and 0.06 volt in each case. 

Instrumentation. A Rank Bros, micro-electrophoresis unit was used in those studies, with a specially made quartz cell having a 6 cm. path length of rectangular inside cross-section (l mm thick, 10 mm deep) in which the Komagata equation (25) predicts zero mobility of the liquid phase in planes located at 0.612 of the distance b from the center plane of the cell to the wall. In electrophoresis experiments 300 to 1200 volts were applied to the cell and mobilities measured in planes a distance h from the center plane. The results were graphed as observed velocity versus (h/b)z as proposed by van Gils (26J, and if the straight lines characteristic of perfect parabolic flow resulted, the electrophoretic mobilities (v ) observed at h/b=0.612 were considered acceptable for calculation of zeta-potential. Zeta-potentials were calculated by the Huckel equation (27) ... 

Some particularly interesting observations in this field have been made by Abramson.20 He found that particles when coated with a film of proteins have electrophoretic mobilities which are characteristic not of the particle but of the protein. This was found to be true for glass, collodion, quartz particles, and droplets of mineral oil, using various proteins. Fig. 10 represents some typical results of measure-... 

Electrophoretic mobilities of quartz and clays, both isolated from Berea sandstone, and of calcite and dolomite in three different brines are shown as a function of pH in Figure 9 (74). These results are unique in that they were obtained with brines of higher ionic strength than are usually used in the measurement of solid surface charge. All three brines have the same ionic strength (0.406 mol/L) but differ in composition. The reservoir brine contains significant levels of divalent cations, which are mostly Ca2+. Electrophoretic mobilities at pH 7, also taken from reference 74, are listed in Table VI. 

As mentioned earlier, the magnitude of EOF on PT devices is 10 times lower than that in common microfabrication substrates such as glass, quartz, and PDMS. While the EOF in these popular materials can be raised by chemical or physical modification of the surface (activation by oxygen plasma or sodium hydroxide), similar treatment of PT chips does not yield the same enhancement. The use of sodium hydroxide is not recommended because it attacks the toner surface rapidly (in a few minutes), even at low concentration. However, the low EOF can certainly be an advantage for the analysis of analytes with similar electrophoretic mobilities. One strategy to obtain a simple microdevice but with greater EOF is the fabrication of glass-toner microchips. ... 

Electrophoretic Mobilities. The electrophoretic mobilities reported in Figures 4 and 6 were measured using a Rank Brother apparatus Mark II and flat quartz cell at 25 C. At least 20 particles were timed at both stationary layers. The error is within 5 to 10%. 

Various planar membrane models have been developed, either for fundamental studies or for translational applications monolayers at the air-water interface, freestanding films in solution, solid supported membranes, and membranes on a porous solid support. Planar biomimetic membranes based on amphiphilic block copolymers are important artificial systems often used to mimic natural membranes. Their advantages, compared to artificial lipid membranes, are their improved stability and the possibility of chemically tailoring their structures. The simplest model of such a planar membrane is a monolayer at the air-water interface, formed when amphiphilic molecules are spread on water. As cell membrane models, it is more common to use free-standing membranes in which both sides of the membrane are accessible to water or buffer, and thus a bilayer is formed. The disadvantage of these two membrane models is the lack of stability, which can be overcome by the development of a solid supported membrane model. Characterization of such planar membranes can be challenging and several techniques, such as AFM, quartz crystal microbalance (QCM), infrared (IR) spectroscopy, confocal laser scan microscopy (CLSM), electrophoretic mobility, surface plasmon resonance (SPR), contact angle, ellipsometry, electrochemical impedance spectroscopy (EIS), patch clamp, or X-ray electron spectroscopy (XPS) have been used to characterize their... 

The parabola method makes it possible to measure the potential of cell walls. Usually, the cell is made of quartz, and the parabola method thus offers the possibility of determining the lEP of one material that has already been extensively studied. The potentials of macroscopic specimens of other materials can also be determined from the mobility profile [273-275] by replacement of the original cell wall of a commercial electrophoretic cell by a flat specimen of the material of interest. For example, in [276], the lEP of a basal plane of mica found from the mobility profile was different from the lEP of a mica dispersion. Only a few types of electrophoretic devices (most of which are no longer available on the market) can be used to determine potentials by means of electro-osmosis. 

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