Focal conic array in patterned microchannels near the 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. Focal conic defects can be recovered when heated to the nematic (or cholesteric) phase, and cooled back to smectic. This phenomenon of memory of defects is also seen in reverse, with the orientation of defects in the nematic phase being “remembered” upon cooling to smectic[1] or toron-like defects in the cholesteric phase reversibly transforming into focal conics[2]. We demonstrate that the extent to which an array of focal conic domains can be recovered depends on the maximum heating temperature, and we seek to understand how much this memory is affected by the phase transition itself or by further heating above the phase transition. To do this, we compare a nematic system with a weakly chiral system in which the positions of focal conic domains are induced by a patterned microchannels with curved boundaries and show that, for our particular system, it is possible to quantify the geometric memory. To this purpose, we identify a quantitative measurement of “memory” for focal conic domains in smectic A liquid crystals that undergo a transition to either nematic or cholesteric liquid crystals.

[1] Suh, Ahram et al. Soft matter (2019).

[2] Hare, Sean M et al. Materials 13 (2020).