Measurement and interpretation of electrokinetic phenomena. J Colloid Interface Sci

University of Granada, Granada, Spain.
Journal of Colloid and Interface Science (Impact Factor: 3.37). 06/2007; 309(2):194-224. DOI: 10.1016/j.jcis.2006.12.075
Source: PubMed

ABSTRACT 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 zeta-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 zeta-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 zeta-potential is that electrokinetic theories be correctly used and applied within their range of validity. Basic theories and their application ranges are discussed. A thorough description of the main electrokinetic methods is given; special attention is 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 zeta-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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Available from: Fernando González-Caballero, Sep 29, 2015
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    • "The solutions used for pH titration were 0.1 M HCl and 0.1 M NaOH. The electrophoretic mobilities were converted into zeta potential using Smoluchowski's formula [20] [21]. "
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    ABSTRACT: Bovine serum albumin (BSA) and zinc oxide nanoparticles (ZnO NPs) are chosen as a model system to investigate NPs-protein corona complex formation. ZnO NPs with average size of ∼20nm are coated with BSA using covalent and non-covalent conjugation at temperatures of 4°C and 20°C. The interaction mechanism between ZnO NPs and BSA is studied by using UV-vis absorption, fluorescence, synchronous fluorescence and Raman spectroscopy. Raman spectra of BSA in the presence of ZnO NPs are registered for the first time and confirm decreased α-helix content, increased unstructured folding and β-sheet content in BSA structure. The synchronous fluorescence spectra revealed that the hydrophobicity of the tyrosine residue is decreased and that of the tryptophan is increased. The relation of elucidated changes in BSA structure of BSA-coated ZnO NPs cytotoxicity is tested for CHO cell viability and reactive oxygen species (ROS) generation in vitro. Covalent and non-covalent binding of BSA to ZnO NPs reduces ZnO NPs cytotoxicity and ROS generation, however changes in BSA conformation makes corona less protective against ZnO NPs. Copyright © 2015 Elsevier B.V. All rights reserved.
    Colloids and surfaces B: Biointerfaces 07/2015; 135:316-323. DOI:10.1016/j.colsurfb.2015.07.054 · 4.15 Impact Factor
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    • "The streaming current – another electrokinetic phenomenon – is a convective charge transport which is induced if a pressure gradient generates a flow in the EDL. More comprehensive information is available, e.g. in (Delgado et al, 2007). The streaming current measurements are usually conducted in very defined geometries. "
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    ABSTRACT: Electrical charges originate at most solid surfaces in contact with aqueous electrolytes which results in the formation of an Electrical Double Layer. If an external electric field is tangentially applied to the double layer, an electroosmotic flow is induced which can be employed for various applications such as microfluidic pumps. Here, highly porous materials are especially suitable since they generate significant flow rates along with high pump pressures. The models which are currently used to describe the electroosmotic flow through porous substrates are based on the so–called parallel capillary flow model. In terms of packed beds of granular materials, these models have the disadvantages of oversimplifying the geometry to tortuous capillaries while neglecting intra- and interpore connections, varying pore cross sectional geometries as well as the influence of the packed bed walls. In the current research, we employ dimensional reasoning (Buckingham Π theorem) to derive a phenomenological model which relates the electroosmotic flow to the averaged parameters of the packed bed as well as to the relevant physicochemical parameters. A comprehensive set of experiments is carried out to infer a semi-empirical correlation which can be universally applied to packed beds of arbitrary granular materials. Additionally, we derive a dynamic model of the center-of-mass motion of the fluidic parts of the experimental setup. The model allows for an evaluation of the influence of Joule heating without monitoring the temperature in the bed.
    Microfluidics and Nanofluidics 05/2015; DOI:10.1007/s10404-015-1594-0 · 2.53 Impact Factor
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    • "As this influence is rather small and not significant in this case, it is not modelled here. Despite the previously discussed limitations of this measurement technique, the zeta potential is a feasible technique to gain at least qualitative influences on the surface potential and thus on the emulsion stability (Lyklema, 2000; Marinova et al., 1996; Rambhau, 1978), although the measured value may not be equal with the existent surface potential (however it is induced) (Delgado et al., 2007). The use of a Gibbs isotherm may be more appropriate in the case of liquid/liquid systems (Lyklema, 2000), but significant surface tension measurements were not available. "
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    ABSTRACT: The drop size distribution is an essential process variable in liquid/liquid systems and relevant in many technical applications. It can be described by population balance equations. A coalescence efficiency model was developed to be able to describe the well-known coalescence inhibition due to changing pH value or salt concentration. The model includes the attractive van der Waals and repulsive electrostatic force according to the DLVO theory into the population balance equation framework. This DLVO model can extend existing simulations in a straightforward manner due to a conceptual implementation. Moreover, zeta potential measurements were performed and the model was applied to simulate experiments in a stirred tank. Hence, the drop size distribution could be predicted well with changing pH value. The results are discussed in comparison to simulations with existing models in literature.
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