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Article Dans Une Revue Journal of Physics: Condensed Matter Année : 2002

Structure and dynamics in colloidal and porous charged media

Résumé

Two examples of charged media in water are studied by numerical simulations: aqueous solutions of highly asymmetrical electrolytes (large and highly charged spherical particles Surrounded by small and slightly charged counterions) and a swelling clay (charged plane sheets surrounded by small counterions). In the former example. Brownian dynamics (BID) showed that the mean number of counterions in the vicinity of polyions nearly balances the charge of the macroion and that the turnover of the small ions in this region is important. The effect of hydrodynamic interactions on the dynamics is weak for small ions but is great for macroions. On the other hand, the relative decrease of the macroion self-diffusion coefficients is more important than that of counterions. Moreover, the small ions retain a relatively high self-diffusion coefficient at the highest concentration, a concentration at which the macroions freeze. BD simulation was also used to obtain the distribution of counterions Na+ between the sheets of a fairly hydrated montmorillonite. The obtained profile was very similar to those we obtained by atomic simulations (Monte Carlo and molecular dynamics) and by a Poisson-Boltzmann treatment. It justifies the description of the solvent as a continuum as soon as the system is hydrated enough. However, for less hydrated states of the clay (mono- or bi-layer of water), only atomic simulations can bring exploitable information. We showed that, according to whether the counterion is Na+ and/or Cs+, the behaviours in the bihydrated clay are very different: although Na+ is easily hydrated and is located in the middle of the pores, Cs+ remains close to the negative surfaces of the sheets and its preferential paths along the surface sites can be underscored from obtained trajectories.
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Dates et versions

hal-00168671 , version 1 (29-08-2007)

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  • HAL Id : hal-00168671 , version 1

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Virginie Marry, Frédéric Grün, Christian M. Simon, Marie Jardat, Pierre Turq, et al.. Structure and dynamics in colloidal and porous charged media. Journal of Physics: Condensed Matter, 2002, 40, pp.9207-9221. ⟨hal-00168671⟩
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