Nematic and lamellar liquid-crystalline phases in suspensions of charged silica-coated gibbsite platelets

Computer simulations, theoretical investigations and experiments carried out over the last 20 years have demonstrated that suspensions of hard plate-like colloids display a rich liquid-crystal phase behaviour including nematic and columnar phases. Recently, it has become clear that charged colloidal platelets display an even richer phase behaviour including smectic A and smectic B phases. Here, we report on the formation of liquid crystals in suspensions of charged silica-coated gibbsite platelets in dimethylformamide in the presence of 1 mM salt and without added salt. A nematic phase is observed in the system with added salt, while in the system without added salt a lamellar (smectic A) liquid-crystalline phase is formed as demonstrated by optical observations and synchrotron small angle X-ray scattering measurements. The observed phases are in contrast with the columnar phase that would be expected if the platelets were interacting through hard-core repulsions. A bifurcation analysis suggests that, on ...