Confinement of colloidal smectic phases

We report on the confinement of colloidal liquid crystals in three dimensional chambers. We exploit silica rods’ relatively large density difference with respect to the dispersing solvent to study isotropic, nematic and smectic phases confined into a single chamber. Combining laser scanning confocal microscopy and soft-lithography techniques enables us to characterize the configurations down to the single particle level. We focus on the smectic phase observed in direct vicinity of the bottom wall. We first consider chambers with square footprint finding occurrences of the smectic bridge state, characterized by two parallel disclination lines, in good agreement with simulation of 2-dimensional hard rods. We then examine the case of topologically different annular chambers. By progressively varying the confinement from a disk to a thin annulus we induce a transition from the smectic bidge state, formely found in square, to the smectic ring state with distinctive edge dislocations. The results are compared to very recent density functional theory calculations.