Microbiologia

C. R. Mecanique 336 (2008) 782–787 http://france.elsevier.com/direct/CRAS2B/

Electro-osmosis in gels: Application to Agar-Agar
Fabien Cherblanc ∗ , Jérôme Boscus, Jean-Claude Bénet
Laboratoire de mécanique et génie civil, UMR CNRS 5508, Université Montpellier 2, CC 048, place Eugène Bataillon, 34095 Montpellier, France Received 17 April 2008; accepted 8 September 2008 Available online 10October 2008 Presented by Michel Combarnous

Abstract Widely used in food- and bio-engineering as a reference material, Agar-Agar gel is the focus of an experimental investigation concerning the electro-osmosis phenomenon. After presenting the experimental methods, one trial is discussed in detail. A fair reproducibility of results is obtained, and the averaged electro-osmotic permeability isprovided. This value lies in the range generally measured on various kind of soils, even if Agar-Agar gel does not share any micro-structural characteristics with soils. To cite this article: F. Cherblanc et al., C. R. Mecanique 336 (2008). © 2008 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved. Résumé Electro-osmose dans les gels : Application au gel d’Agar-Agar. Largementutilisé en bio-ingénierie comme un matériau modèle, le gel d’Agar-Agar est l’objet d’une étude expérimentale relative au phénomène d’électro-osmose. Après la présentation des méthodes expérimentales, un essai est discuté en détail. Une bonne reproductibilité des résultats est observée, et une valeur moyenne de la perméabilité électro-osmotique du gel d’Agar-Agar est proposée. Ce résultat est enaccord avec la plage de valeurs mesurées sur une large gamme de géo-matériaux, même si les caractéristiques micro-structurales du gel d’Agar-Agar sont très éloignées de celles d’un sol. Pour citer cet article : F. Cherblanc et al., C. R. Mecanique 336 (2008). © 2008 Académie des sciences. Published by Elsevier Masson SAS. All rights reserved.
Keywords: Porous media; Agar-Agar gel; electro-osmosisMots-clés : Milieu poreux ; gel d’Agar-Agar ; électro-osmose

1. Introduction Many geological and biological media (clays, cartilages, . . . ) exhibit swelling-shrinkage behaviour when submitted to hydraulic, electric or osmotic stresses. Since similar theoretical approaches are involved, the coupling between the mechanical behaviour and transport phenomena is of great interest in geomechanicaland biomedical engineering [1]. The strains observed stem from liquid phase transport phenomena that take place in porous media (osmosis, electroosmosis). These coupling effects observed at the macroscale generally results from the electrical interactions at the
* Corresponding author.

E-mail address: chb@lmgc.univ-montp2.fr (F. Cherblanc). 1631-0721/$ – see front matter © 2008 Académie dessciences. Published by Elsevier Masson SAS. All rights reserved. doi:10.1016/j.crme.2008.09.004

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microscale [2]. The link between these two scales of description and the physical properties associated can be derived theoretically using an upscaling procedure [3], but also relies on a macroscopic experimental characterization sincethe microscopic quantities are hardly measurable. When a porous medium saturated by an ionic solution exhibits some fixed electrical charges at the surface of the solid phase, the spatial distribution of ions and cations in the liquid phase is ruled by the electrical double layer theory [2]. If the fixed charges are negatives, excess mobile cations are required in the solution to ensureelectroneutrality. When submitted to an external electric field, these excess mobile cations exert an additional momentum to the pore fluid that drives the liquid phase toward the cathode. This net movement of fluid relative to the solid structure under an imposed electric potential gradient is called electro-osmosis [4]. In practice, the electro-osmotic velocity is described at a macroscopic scale by vL =...