Formation of liquid-crystal cholesteric pitch in the centimeter range

The formation of a macroscopic cholesteric spiral in a nematic liquid crystal (LC) doped with chiral molecules is studied. Measurements of the orientation of the disclination line formed in a LC theta-cell manufactured with one substrate having linear in-plane alignment and the opposing substrate having circular alignment showed the formation of a uniform macroscopic cholesteric spiral with a pitch length of centimeters. We found a linear dependence of the reciprocal pitch p(-1) on the concentration c in a wide range of p, extending from micrometers up to several centimeters. It suggests that the pitch of a spiral in a nematic LC doped with chiral dopants results from a long-range orientation owing to short-range chiral interactions in the vicinity of the chiral additive.