Electrokinetic adsorption

Lee, C. T. Clark, D. E. 1985. Electrokinetics, adsorption and colloid study of simulated nuclear waste glasses leached in aqueous solutions. In Jantzen, C. M., Stone, J. A. Ewing, R. C. (eds) Scientific Basis for Nuclear Waste Management VIII. Materials Research Society Symposia Proceedings, 44, 221-228. 

The use of asbestos has been greatly diminished because of its identification with health hazards. There have been proposed replacement materials such as the Zeta Plus filter media from the AMF Cuno Division, consisting of a composite of cellulose and inorganic filter aids that have a positive charge and provide an electrokinetic attraction to hold colloids (usually negatively charged). These media therefore provide both mechanical straining and electrokinetic adsorption. 

Protein adsorption has been studied with a variety of techniques such as ellipsome-try [107,108], ESCA [109], surface forces measurements [102], total internal reflection fluorescence (TIRE) [103,110], electron microscopy [111], and electrokinetic measurement of latex particles [112,113] and capillaries [114], The TIRE technique has recently been adapted to observe surface diffusion [106] and orientation [IIS] in adsorbed layers. These experiments point toward the significant influence of the protein-surface interaction on the adsorption characteristics [105,108,110]. A very important interaction is due to the hydrophobic interaction between parts of the protein and polymeric surfaces [18], although often electrostatic interactions are also influential [ 116]. Protein desorption can be affected by altering the pH [117] or by the introduction of a complexing agent [118]. 

Kovat s retention index (p. 575) liquid-solid adsorption chromatography (p. 590) longitudinal diffusion (p. 560) loop injector (p. 584) mass spectrum (p. 571) mass transfer (p. 561) micellar electrokinetic capillary chromatography (p. 606) micelle (p. 606) mobile phase (p. 546) normal-phase chromatography (p. 580) on-column injection (p. 568) open tubular column (p. 564) packed column (p. 564) peak capacity (p. 554)... 

The adsorption of ions at insulator surfaces or ionization of surface groups can lead to the formation of an electrical double layer with the diffuse layer present in solution. The ions contained in the diffuse layer are mobile while the layer of adsorbed ions is immobile. The presence of this mobile space charge is the source of the electrokinetic phenomena.t Electrokinetic phenomena are typical for insulator systems or for a poorly conductive electrolyte containing a suspension or an emulsion, but they can also occur at metal-electrolyte solution interfaces. 

During the formation of polycation-polyanion multilayer coatings on halloysite, we monitored the surface potential (electrokinetic zeta potential). Initially negative halloysite (—40 mV) was converted to a positive surface with polycation layer adsorption in the first step of the LbLassembly (figure 14.10). Adsorption of polyanions in the second step re-established the negative charge which was reversed... 

Electrostatic vs. Chemical Interactions in Surface Phenomena. There are three phenomena to which these surface equilibrium models are applied regularly (i) adsorption reactions, (ii) electrokinetic phenomena (e.g., colloid stability, electrophoretic mobility), and (iii) chemical reactions at surfaces (precipitation, dissolution, heterogeneous catalysis). 

Modifications of surface layers due to lattice substitution or adsorption of other ions present in solution may change the course of the reactions taking place at the solid/liquid interface even though the uptake may be undetectable by normal solution analytical techniques. Thus it has been shown by electrophoretic mobility measurements, (f>,7) that suspension of synthetic HAP in a solution saturated with respect to calcite displaces the isoelectric point almost 3 pH units to the value (pH = 10) found for calcite crystallites. In practice, therefore, the presence of "inert" ions may markedly influence the behavior of precipitated minerals with respect to their rates of crystallization, adsorption of foreign ions, and electrokinetic properties. 

Bendahl, L., Hansen, S. H., and Gammelgaard, B. (2001). Capillary modified by noncovalent anionic polymer adsorption for the capillary zone electrophoresis, micellar electrokinetic capillary chromatography and capillary electrophoresis mass spectrometry. Electrophoresis 22, 2565-2573. 

The presence of pre-adsorbed polyacrylic acid significantly reduces the adsorption of sodium dodecylsulfonate on hematite from dilute acidic solutions. Nonionic polyacrylamide was found to have a much lesser effect on the adsorption of sulfonate. The isotherm for sulfonate adsorption in absence of polymer on positively charged hematite exhibits the typical three regions characteristic of physical adsorption in aqueous surfactant systems. Adsorption behavior of the sulfonate and polymer is related to electrokinetic potentials in this system. Contact angle measurements on a hematite disk in sulfonate solutions revealed that pre-adsorption of polymer resulted in reduced surface hydrophobicity. 

Electrokinetic Measurements. Electrophoretic mobilities were measured with a flat-cell apparatus manufactured by Rank Brothers, Cambridge, England. In addition, several mobility values were checked for accuracy with a Zeta Meter, New York. Mobilities were determined with a small volume of the suspension (approximately 25 cc) that had been prepared for the adsorption experiments. The pH of the solution was measured prior to determining the electrophoretic mobilities, which involved measuring the velocities of five to ten particles in each direction. An average value of the mobilities was recorded. Samples containing the flocculated particles were dipped into an ultrasonic bath for approximately one second prior to making the pH and mobility measurements. 

The adsorption behavor of surfactant onto particles in the absence and presence of pre-adsorbed polymer was determined. Electrokinetic studies of the system were made. Contact angle measurements yielded information on the level of hydrophobicity achieved at various additions of polymer and collector. 

Adsorption and Electrokinetic Effects of Amino Acids on Rutile and Hydroxyapatite... 

The mechanism of interaction of amino acids at solid/ aqueous solution interfaces has been investigated through adsorption and electrokinetic measurements. Isotherms for the adsorption of glutamic acid, proline and lysine from aqueous solutions at the surface of rutile are quite different from those on hydroxyapatite. To delineate the role of the electrical double layer in adsorption behavior, electrophoretic mobilities were measured as a function of pH and amino acid concentrations. Mechanisms for interaction of these surfactants with rutile and hydroxyapatite are proposed, taking into consideration the structure of the amino acid ions, solution chemistry and the electrical aspects of adsorption. 

FUERSTENAU ET AL. Adsorption, Electrokinetic Effects of Amitio Adds 313... 

Adsorption and Electrokinetic Behavior of Hydroxyapatite. The adsorption densities of glutamic acid and lysine on hydroxyapatite are shown in Flgures b and 7. The change in slope of the adsorption isotherm at 10 M glutamic acid is considered to be due to a... 

The adsorption of amino acids on rutile and hydroxyapatite exhibits some characteristics of specific adsorption. The results can be interpreted in terms of electrostatic models of adsorption, however, if reorientation of adsorbed molecules is taken into consideration. The electrokinetic behavior of hydroxyapatite in glutamic acid is complicated because of a chemical reaction, possibly involving calcium ions. The study shows that it is necessary to take into consideration the orientation of adsorbed molecules, particularly for zwitterionic surfactants. 

Adsorption and electrokinetic effects of amino acids, solid-aqueous interface, 311-26 Adsorption density, equilibrium PAA at various pH values, 299f PAA on hematite, 304f SDS with and without polymer, 298f,303f... 

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