Pitch Measurements on Chirally Doped Ferroelectric Nematics

Abstract

Following the recent discovery of the ferronematic liquid crystal phase, it is important to explore the material’s properties as well as to devise methods of identification. In this report, an experimental method to measure the helical pitch of the ferronematic material RM734 doped with a chiral dopant S811 by use of the so-called circularly rubbed cell method is explored for the first time and compared to other methods. The method utilises a cell of two substrates linearly and circularly rubbed of which the pitch is measured from the resulting deviation angle of disclination lines induced by this particular geometry. The results showed that the pitch in the polar ferroelectric phase behaved similarly to that of the non-polar nematic phase but with a small change in magnitude at the phase transition to the polar phase. Phase transition temperatures could also be determined and a negative trend between the doping concentrations and transition temperatures for both the isotropic to nematic and nematic to ferronematic phases was observed. Finally, a first attempt was made at in-situ ultraviolet light-induced polymer stabilisation of the ferronematic liquid crystal by use of photoreactive monomers mixed into the liquid crystal. This attempt yielded inconclusive results as polymer stabilisation was not observed, yet there seemed to be some adverse effects on the liquid crystal.