Colloids electrokinetic effects

A.J.G. Blesa, M.A. (1988) The dissolution of magnetite by nitrilotriacetatoferrate(II). J. Chem. Soc. Earaday Trans. I. 84 9-18 Delgado, A. Torrent, J. (2000) Phosphorus forms and desorption patterns in heavily fertilized calcareous and limed acid soils. Soil Sci. Soc. Am. J. 64 2031-2037 Delgado, A.V. Gonzalez-Caballero, F. (1998) Inorganic particles as colloidal models. Effects of size and shape on the electrokinetics of hematite (a-Fe203). Croatica Chemica Acta 71 1087-1104... 

In 1808, Rous, a colloid chemist, observed that imposing an electric potential difference across a porous wet clay led not only to the expected flow of electricity, but also to a flow of water. He later applied hydrostatic pressure to the clay and observed a flow of electricity. This experiment displayed the electrokinetic effect and demonstrated the existence of coupled phenomena where a flow may be induced by forces other than its own driving force. Therefore, the electric current is evidently caused by the electromotive force, but it may also be induced by the hydrostatic pressure. When two... 

To characterize a surface electrokinetically involves the measurement of one of the above electrokinetic effects. With disperse colloidal systems it is practical to measure the particle electrophoretic mobility (induced particle velocity per unit applied electric field strength). However, for a nondisperse system one must measure either an induced streaming potential or an electro-osmosis fluid flow about the surface. 

The electrokinetic effect is one of the few experimental methods for estimating double-layer potentials. If two electrodes are placed in a colloidal suspension, and a voltage is impressed across them, the particles move toward the electrode of opposite charge. For nonconducting solid spherical particles, the equation controlling... 

Delgado, A.V., and Gonzalez-Cahallero, E, Inorganic particles as colloidal models. Effects of size and shaj c on the electrokinetics of hematite (0. -Ee2OLj), Croat. Chem. Acta, 71, 1087, 1998. 

Closely related to this is the general problem in the whole chemical industry of the separation of solids from liquids. The processes of thickening, flocculation, dewatering, and filtration are all intimately controlled by the forces and structures arising in colloidal systems. The improvements brought about by the use of electroseparation processes depend on the exploitation of the electrokinetic effects discussed in Chapter 6. 

Sennett P, Olivier JP (1965) Colloidal Dispersions. Electrokinetic Effects and the Concept of Zeta Potential. In Gushee DE (ed) Chemistry and Physics of Interfaces. Amer Chem Soc, Washington, D.C. 

Baygents, J.C., Electrokinetic effects on the dielectric response of colloidal particles dielectrophoresis and electrorotation. Colloids Surf. A, 92, 67, 1994. 

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. 

Two nucleation processes important to many people (including some surface scientists ) occur in the formation of gallstones in human bile and kidney stones in urine. Cholesterol crystallization in bile causes the formation of gallstones. Cryotransmission microscopy (Chapter VIII) studies of human bile reveal vesicles, micelles, and potential early crystallites indicating that the cholesterol crystallization in bile is not cooperative and the true nucleation time may be much shorter than that found by standard clinical analysis by light microscopy [75]. Kidney stones often form from crystals of calcium oxalates in urine. Inhibitors can prevent nucleation and influence the solid phase and intercrystallite interactions [76, 77]. Citrate, for example, is an important physiological inhibitor to the formation of calcium renal stones. Electrokinetic studies (see Section V-6) have shown the effect of various inhibitors on the surface potential and colloidal stability of micrometer-sized dispersions of calcium oxalate crystals formed in synthetic urine [78, 79]. 

Electroviscous effect occurs when a small addition of electrolyte a colloid produces a notable decrease in viscosity. Experiments with different salts have shown that the effective ion is opposite to that of the colloid particles and the influence is much greater with increasing oxidation state of the ion. That is, the decrease in viscosity is associated with decreased potential electrokinetic double layer. The small amoimt of added electrolyte can not appreciably affect on the solvation of the particles, and thus it is possible that one of the determinants of viscosity than the actual volume of the dispersed phase is the zeta potential. 

Hunter, R. J., Zeta Potentials in Colloid Science Principles and Applications, Academic Press, London, 1981. (Advanced. A research-level monograph on electrokinetic phenomena and electroviscous and viscoelectric effects.)... 

Amankonah J.F. and Somasundran P. (1985) Effects of dissolved mineral species on the electrokinetic behavior of calcite and apatite. Colloids and Surfaces 15, 335-353. 

During the past two decades, much attention has been drawn in this area and advances have been made in theoretical analysis concerning the applicability of Eq. (1) in a variety of systems. This chapter presents the state of understanding of the electrophoretic motion of colloidal particles under various conditions. We first introduce the basic concept and fundamental electrokinetic equations for electrophoretic motion. Then, we review some recent studies on the mobility of a single particle, the boundary effects and the particle interactions in electrophoresis. In addition, a few theoretical methods, which have been used to investigate the boundary effects and particle interactions, will be highlighted and demonstrated in the context. 

The ODN adsorption onto cationic microgel poly(N-isopropylacrylamide) particles was reported to be dramatically affected by the salinity of the incubation medium [9] as illustrated in Fig. 6. The observed result was related to (i) the reduction in attractive electrostatic interactions between ODN molecules and the adsorbent and (ii) the drastic effect of ionic strength on the physico-chemical properties of such particles [17, 27]. In fact, the hydrodynamic size, the swelling ability, the electrokinetic properties, and the colloidal stability are dramatically affected by pH, salt concentration, and the medium temperature [27]. 

Electroacoustics — Ultrasound passing through a colloidal dispersion forces the colloidal particles to move back and forth, which leads to a displacement of the double layer around the particles with respect to their centers, and thus induces small electric dipoles. The sum of these dipoles creates a macroscopic AC voltage with the frequency of the sound waves. The latter is called the Colloid Vibration Potential (CVP) [i]. The reverse effect is called Electrokinetic Sonic Amplitude (ESA) effect [ii]. See also Debye effect. 

For well-dispersed colloid systems, particle electrophoresis has been the classic method of characterization with respect to electrostatic interactions. However, outside the colloidal realm, i.e., in the rest of the known world, the measurement of other electrokinetic phenomena must be used to characterize surfaces in this respect. The term electrokinetic refers to a number of effects induced by externally applied forces at a charged interface. These effects include electrophoresis, streaming potential, and electro-osmosis. 

The colloid vibration potential (difference) E or CVP is the a.c. potential difference measured between two Identical relaxed electrodes, placed in the dispersion if the latter Is subjected to an (ultra)sonlc field. CVP Is a particular case of the more general phenomenon, ultrasonic vibration potential (UVP), applying to any system, whether or not colloids are present. This field sets the particles into a vibrating motion, as a result of which the centres of particle charge and countercharge are periodically displaced with respect to each other. This phenomenon is the a.c. equivalent of that observed in the Dorn effect. Counterpart to this is the electrokinetic sonic amplitude, ESA, the amplitude of the (ultra)sonlc field created by an a.c, electric field in a dispersion. 

Figure 4.12. Apparent electrokinetic potential as a function of the outer Helmholtz plane potential, when the slip process Is determined by the viscoelectrlc effect. J = 10.2 X 10 V m c Is the concentration of the (1-1) electrolyte In M. (Redrawn from J. Lyklema. Colloids Surf. A92 (1994) 41.)...

Allegedly pure materials often contain specifically adsorbing ions as impurities. These impurities induce a shift in the lEP, and special cleaning methods are necessary to remove them. Most likely some unusual pH values reported as pristine lEP for certain materials (Table 3.1, and 3.3) are caused by specific adsorption of impurities, namely, anionic impurities induce a low lEP and cationic—a high lEP. Lack of coincidence between the lEP and CIP (cf. Fig. 4.12) and unsymmetrical shape of the electrokinetic curves corroborates this assertion. The errors caused by specific adsorption of anionic impurities are more common than the cation effects. The COi and SiOj errors in electrokinetic measurements and difficulties in removal of multivalent anions, which are present in solutions used to prepare monodispersed colloids, can serve as a few examples (cf. Section 3.I.B.1). 

Electroacoustic method, 80 Electrokinetic potential effect on interaction energy between colloidal particles, 248 effect of ionic strength on, 66 of macroscopic samples, 79 of oxides, effect of hydration time on, 76 relationship to thd. 649, 656 in solution of weak electrolyte, 242 at very high ionic strengths, 266, 267 Electronegativity, correlation with PZC, 213... 

Kallay, N., Colic, M., Fuerstenau, D. W., Jang, H. M., and Matijevic, E. (1994). Lyotropic effect in surface charge, electrokinetics, and coagulation of a rutile dispersion. Colloid Polym. Sci. 272, 554-561. 

---