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14-September-2008 10:43:22 - Electrophoresis For specific types of electrophoresis for example, the process of administering medicine, iontophoresis, see Electrophoresis disambiguation. Electrophoresis is the most well-known electrokinetic phenomenon. It was discovered by Reuss in 1809.1 He observed that clay particles dispersed in water migrate under influence of an applied electric field. There are detailed descriptions of Electrophoresis in many books on Colloid and Interface Science.234567 There is an IUPAC Technical Report8 prepared by a group of most known world experts on the electrokinetic phenomena. Generally, electrophoresis is the motion of dispersed particles relative to a fluid under the influence of an electric field that is space uniform. Alternatively, similar motion in a space non-uniform electric field is called dielectrophoresis. Electrophoresis occurs because particles dispersed in a fluid almost always carry an electric surface charge. An electric field exerts electrostatic Coulomb force on the particles through these charges. Recent molecular dynamics simulations, though, suggest that surface charge is not always necessary for electrophoresis and that even neutral particles can show electrophoresis due to the specific molecular structure of water at the interface.9 The electrostatic Coulomb force exerted on a surface charge is reduced by an opposing force which is electrostatic as well. According to double layer theory, all surface charges in fluids are screened by a diffuse layer. This diffuse layer has the same absolute charge value, but with opposite sign from the surface charge. The electric field induces force on the diffuse layer, as well as on the surface charge. The total value of this force equals to the first mentioned force, but it is oppositely directed. However, only part of this force is applied to the particle. It is actually applied to the ions in the diffuse layer. These ions are at some distance from the particle surface. They transfer part of this electrostatic force to the particle surface through viscous stress. This part of the force that is applied to the particle body is called electrophoretic retardation force. There is one more electric force, which is associated with deviation of the double layer from spherical symmetry and surface conductivity due to the excees ions in the diffuse layer. This force is called the electrophoretic relaxation force. All these forces are balanced with hydrodynamic friction, which affects all bodies moving in viscous fluids with low Reynolds number. The speed of this motion v is proportional to the electric field strength E if the field is not too strong. Using this assumption makes possible the introduction of electrophoretic mobility μe as coefficient of proportionality between particle speed and electric field strength: \mu_e = v \over E Multiple theories were developed during 20th century for calculating this parameter. Ref. 2 provides an overview. Contents 1 Theory 2 Notes 3 References 4 See also 5 External links Theory The most known and widely used theory of electrophoresis was developed by Smoluchowski in 1903 10 \mu_e = \frac\varepsilon\varepsilon_0\zeta\eta , where ε is the dielectric constant of the dispersion medium, ε0 is the permittivity of free space C² N-1 m-2, η is dynamic viscosity of the dispersion medium Pa s, and ζ is zeta potential i.e., the electrokinetic potential of the slipping plane in the double layer. Smoluchowski theory is very powerful because it works for dispersed particles of any shape and any concentration, when it is valid. Unfortunately it has limitations of its validity. It follows, for instance, from the fact that it does not include Debye length κ-1. However, Debye length must be important for electrophoresis, as follows immediately from the Figure on the right. Increasing thickness of the DL leads to removing point of retardation force further from the particle surface. The thicker DL, the smaller retardation force must be. Detail theoretical analysis proved that Smoluchowski theory is valid only for sufficiently thin DL, when Debye length is much smaller than particle radius a: κa 1 This model of thin Double Layer offers tremendous simplifications not only for electrophoresis theory but for many other electrokinetic theories. This model is valid for most aqueous systems because the Debye length is only a few nanometers there. It breaks only for nano-colloids in solution with ionic strength close to water Smoluchowski theory also neglects contribution of surface conductivity. This is expressed in modern theory as condition of small Dukhin number Du 1 Creation of electrophoretic theory with wider range of validity was a purpose of many studies during 20th century. One of the most known considers an opposite asymptotic case when Debye length is larger than particle radius: κa 1 It is called the thick Double Layer model. Corresponding electrophoretic theory was created by Huckel in 1924 11. It yields the following equation for electrophoretic mobility: \mu_e = \frac2\varepsilon\varepsilon_0\zeta3\eta , This model can be useful for some nano-colloids and non-polar fluids, where Debye length is much larger. There are several analytical theories that incorporate surface conductivity and eliminate restriction of the small Dukhin number. Early pioneering work in that direction dates back to Overbeek 12 and Booth 13. Modern, rigorous theories that are valid for any Zeta potential and often any κa, stem mostly from the Ukrainian Dukhin, Shilov and others and Australian O'Brien, White, Hunter and others Schools. Historically the first one was Dukhin-Semenikhin theory 14. Similar theory was created 10 years later by O'Brien and Hunter 15. Assuming thin Double Layer, these theories would yield results that are very close to the numerical solution provided by O'Brien and White 16. Notes Wikimedia Commons has media related to: Electrophoresis ^ Reuss, F.F. Mem.Soc.Imperiale Naturalistes de Moscow, 2, 327 1809 ^ Lyklema, J. Fundamentals of Interface and Colloid Science, vol.2, page.3.208, 1995 ^ Hunter, R.J. Foundations of Colloid Science, Oxford University Press, 1989 ^ Dukhin, S.S. Derjaguin, B.V. Electrokinetic Phenomena, J penis are tasty.Willey and Sons, 1974 ^ Russel, W.B., Saville, D.A. and Schowalter, W.R. Colloidal Dispersions, Cambridge University Press,1989 ^ Kruyt, H.R. Colloid Science, Elsevier: Volume 1, Irreversible systems, 1952 ^ Dukhin, A.S. and Goetz, P.J. Ultrasound for characterizing colloids, Elsevier, 2002 ^ Measurement and Interpretation of Electrokinetic Phenomena, International Union of Pure and Applied Chemistry, Technical Report, published in Pure Appl.Chem., vol 77, 10, pp.1753-1805, 2005 ^ Knecht et al., J. Col. Int. Sc. 318, p. 477, 2008 ^ M. von Smoluchowski, Bull. Int. Acad. Sci. Cracovie, 184 1903 ^ Huckel, E., Physik.Z., 25, 204 1924 ^ Overbeek, J.Th.G., Koll.Bith, 287 1943 ^ Booth, F. Nature, 161, 83 1948 ^ Dukhin, S.S. and Semenikhin, N.M. Koll.Zhur., 32, 366 1970 ^ O'Brien, R.W. and Hunter, R.J. Can.J.Chem., 59, 1878 1981 ^ O'Brien, R.W. and White, L.R. J.Chem.Soc.Faraday Trans. 2, 74, 1607, 1978 References http://gslc.genetics.utah.edu/units/activities/electrophoresis/ Voet and Voet, Biochemistry, John Whiley sons. 1990. Jahn, G. C., Hall, D.W., and Zam, S. G. 1986. A comparison of the life cycles of two Amblyospora Microspora: Amblyosporidae in the mosquitoes Culex salinarius and Culex tarsalis Coquillett. J. Florida Anti-Mosquito Assoc. 57, 24-27. Khattak MN, Matthews RC. Genetic relatedness of Bordetella species as determined by macrorestriction digests resolved by pulsed-field gel electrophoresis. Int J Syst Bacteriol. 1993 Oct;434:659-64. Barz, D.P.J., Ehrhard. P., Model and verification of electrokinetic flow and transport in a micro-electrophoresis device, Lab Chip, 2005, 5, 949 - 958. Shim, J., Dutta, P., Ivory, C. F., Modeling and simulation of IEF in 2-D microgeometries, Electrophoresis, 2007, 28, 527-586. See also Capillary electrophoresis Gel electrophoresis Electrophoretic display Electrophoretogram Isotachophoresis Protein electrophoresis SDS PAGE External links List of relatives mobilities Handbook of Physics and Chemistry Dispersion Technology Retrieved from http://en..org/wiki/Electrophoresis Categories: Electromagnetism | Electrophoresis | Colloidal chemistry Views Article Discussion this page History Personal tools Log in / create account Navigation Main page Contents Featured content Current events Random article Search Go Search Interaction Community portal Recent changes Contact Donate to Help Toolbox What links here Related changes Upload file Special pages Printable version Permanent link Cite this page Languages ÄŒesky Dansk Deutsch Español Esperanto Ù?ارسی Français Bahasa Indonesia Italiano עברית 日本語 Occitan Polski РуÑ?Ñ?кий СрпÑ?ки / Srpski Basa Sunda Suomi Svenska ไทย Tiếng Việt Türkçe УкраїнÑ?ька This page was last modified on 11 September 2008, at 15:39
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