Electro-Optical Properties of Imperfectly Ordered Planar Cholesteric Layers

The electro-optical behaviour of imperfectly ordered planar layers of a mixture of 20% cholesteryl chloride and 80% cholesteryl oleyl carbonate (natural pitch p0 = 0.37 µm) is discussed. Microscopic observations reveal that these layers consist of a number of uniform planar regions with different pitch (p ≠ p0), separated by disclinations. With increasing layer thickness these regions become smaller while the differences in pitch decrease. The electric-field-indueed blue shift of the selective reflections is suggested as resulting from a successive distortion of the planar regions. The observed decrease in blue shift with increasing layer thickness, as well as the absence of this shift in regions with uniform pitch, demonstrate the correlation between the blue shift and the field-induced periodic distortion.