Vol. 28 No. 1
Measurement and Interpretation of Electrokinetic Phenomena (IUPAC Technical Report)
A.V. Delgado, F. González-Caballero, R.J. Hunter, L.K. Koopal, and J. Lyklema
Pure and Applied Chemistry
Vol. 77, No. 10, pp. 1753–1805 (2005)
Electrokinetic phenomena (EKP) can be loosely defined as all those phenomena involving tangential fluid motion adjacent to a charged surface. They are manifestations of the electrical properties of interfaces under steady-state and isothermal conditions. In practice, they are often the only source of information available on those properties. For this reason, their study constitutes one of the classical branches of colloid science, electrokinetics, which has been developed in close connection with the theories of the electrical double layer (EDL) and of electrostatic surface forces.
In this report, the status quo and recent progress in electrokinetics are reviewed. Practical rules are recommended for performing electrokinetic measurements and interpreting their results in terms of well-defined quantities, the most familiar being the ζ-potential or electrokinetic potential. This potential is a property of charged interfaces, and it should be independent of the technique used for its determination. However, often the ζ-potential is not the only property electrokinetically characterizing the electrical state of the interfacial region; the excess conductivity of the stagnant layer is an additional parameter. The requirement to obtain the ζ-potential is that electrokinetic theories be correctly used and applied within their range of validity.
Also in this report, basic theories and their application ranges are discussed and a thorough description of the main electrokinetic methods is given, with special attention paid to their ranges of applicability as well as to the validity of the underlying theoretical models. Electrokinetic consistency tests are proposed in order to assess the validity of the ζ-potentials obtained. The recommendations given in the report apply mainly to smooth and homogeneous solid particles and plugs in aqueous systems; some attention is paid to nonaqueous media and less ideal surfaces.
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