Nematic ordering vs. gelation in suspensions of charged platelets

We study aqueous suspensions of charged gibbsite platelets that show the isotropic (I) to nematic (N) phase transition. This is the first case where the I-N transition in a dispersion of charged colloidal platelets is not impeded by gelation since Langmuir's classic work on dispersions of clay particles more than sixty years ago (J. Chem. Phys., 6 (1938) 873). On increasing particle concentration, our dispersions subsequently show an isotropic, nematic and gel phase. We attribute the shift of the gelation boundary from below to above the I-N transition to the surface modi cation of the gibbsite platelets with aluminium polycations, which are known to enhance the stability of gibbsite colloids significantly.