On shape and electrostatics: competing anisotropies in charged colloidal platelets

S. Jabbari-Farouji 1, J. -J. Weis 2, P. Davidson 3, P. Levitz 4, E. Trizac 1

Charged platelet suspensions, such as swelling clays, disc-like mineral crystallites or exfoliated nanosheets, are ubiquitous in nature. Their puzzling phase behaviours are nevertheless still poorly understood: while Laponite and Bentonite clay suspensions form arrested states at low densities, others, like Beidellite and Gibbsite, exhibit an equilibrium isotropic-nematic transition at moderate densities. These observations raise fundamental questions about the influence of electrostatic interactions on the isotropic-nematic transition and more generally on the organisation of charged platelets. We investigate the competition between anisotropic excluded-volume and electrostatic interactions in suspensions of thin charged disks, by means of Monte-Carlo simulations. We show that the original intrinsic anisotropy of the electrostatic potential between charged platelets, obtained within the non-linear Poisson-Boltzmann formalism, not only captures the generic features of the complex phase diagram of charged colloidal platelets, but also predicts the existence of novel structures and arrested states upon varying density and ionic strength.

  • 1. Laboratoire de Physique Théorique et Modèles Statistiques (LPTMS),
    CNRS : UMR8626 – Université Paris XI - Paris Sud
  • 2. Laboratoire de Physique Théorique d'Orsay (LPT),
    CNRS : UMR8627 – Université Paris XI - Paris Sud
  • 3. Laboratoire de Physique des Solides (LPS),
    CNRS : UMR8502 – Université Paris XI - Paris Sud
  • 4. Physicochimie des Electrolytes, Colloïdes et Sciences Analytiques (PECSA),
    Université Paris VI - Pierre et Marie Curie – ESPCI ParisTech – CNRS : UMR7195