Time resolved studies of the switching behaviour of smectic liquid crystals

The field-induced alignment of a smectic A phase is a complicated process involving director rotation via the interaction with the field and the layer rotation via the molecular interactions. We have investigated the alignment of the smectic A phase of 4-octyl-4′-cyanobiphenyl (8CB). The experiment consists of creating a monodomain sample by cooling the sample in a magnetic field of 7 T. The sample is then turned quickly about an axis parallel to the X-ray beam, but orthogonal to the field. The alignment behaviour is temperature dependent and changes as the rotation angle exceeds 45°. Numerical simulations based on the technique of dissipative particle dynamics were used to gain insights into the experiments. We find that following a rotation, part of the sample disorders and the rest rotates as a collection of domains, in which the integrity of the smectic layer structure is conserved.