This picture, taken by in-situ polarized microscopy at the HFML in The Netherlands, shows the surface pattern formed in smectic liquid crystal 8CB during the nematic-smectic transition in a constant background magnetic field of 7 Tesla. The formation of a striated defects pattern is observed for the first time by lowering the system temperature. This pattern results from the competition of two antagonistic orienting forces acting in the LC cell. The planar field-induced orientation is dominant in the bulk, while a homeotropic alignment is given by the surface of the glass cell. In between these two regions the smectic structure is frustrated and relaxes the constrains by bending to form a stripe-like pattern. Therefore the observed defects do not perturb the system order, but instead are responsible for the establishment of a stable smectic phase. We find that defects form in the plane of the surface, initially in a random direction and subsequently they readjust by breaking and rotating to the field induced direction. Once oriented in the field direction, defects can can develop much faster compared to the growth rate in any another planar direction. The growth speed is found to strongly decrease in higher magnetic fields, where less defects are observed, since the planar orientation becomes dominant. Note the inner structure of the defect pattern that shows a highly regular undulation. It is remarkable how the system can cope with the two competing forces: the homeotropic alignment, as induced by the surface, and the planar alignment promoted by the applied magnetic field, to create the liquid crystalline order.
Jury comment: a liquid crystal mirage of coins
