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 degrees. 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.