Surface frustration and texture instability in smectic-A liquid crystals.

Uniform smectic-A plates, floating freely on top of isotropic droplets, show static instabilities. Above a thickness threshold, the stable state of the smectic plate is an hexagonal network of focal conics. This instability is quantitatively explained by the anisotropy of surfaces tensions, which favors the alignment of smetic layers parallel to the air interface and perpendicular to the isotropic phase. This intrinsic frustration seems general for most smectic-A\ensuremath{\rightarrow}isotropic first-order transitions.