Formation of lamellar structures from spherical particles.

We report disorder to lamellar transition in a system of spherically symmetric particles where the interparticle potential consists of a short-ranged attraction and a longer-ranged repulsion. The system provides a simplified model for aqueous dispersions of colloidal particles and globular proteins that may exhibit stable/metastable clusters or microscopic phases. By using a non-mean-field density functional theory, we predict that under appropriate conditions, a lamellar phase with alternating condensed and dilute layers of particles is thermodynamically more stable than a uniform disordered phase at the same temperature and molecular number density. Formation of the lamellar structure may prohibit the macroscopic fluid-fluid phase transition. At a given condition, the width of the condensed lamellar layers increases with the overall particle density but the trend is opposite for the dilute lamellar layers. A minimal lamellar periodicity is obtained when the condensed and dilute layers have approximately the same thickness.