Focal conic array in patterned microchannels near the cholesteric-smectic phase transition*

It is known that the liquid crystalline smectic-A phase has geometric defects, called focal conic domains, whose size and positions are heavily influenced by their boundaries. We have recently shown that chiral nematic phases have toron-like defects that can, for varying ranges of temperatures, reversibly transform into focal conic domains across the phase transition, displaying geometric memory [1]. We explore a weakly chiral system in which the positions of focal conic domains are controlled by confinement, and these defects are formed as the system relaxes near the phase transition. To study this, we have patterned microchannels with curved boundaries to induce arrays of focal conic domains and explore their formation for a different range of channel geometries. We show that certain defects are topologically protected, and we observe a variety of seemingly equilibrium configurations that are only observed as a result of conditions present at the phase transition.

[1] Hare, Sean M., Beatrice Lunsford-Poe, MinSu Kim, and Francesca Serra. "Chiral Liquid Crystal Lenses Confined in Microchannels." Materials 13, no. 17 (2020): 3761. https://doi.org/10.3390/ma13173761.