Experimental evidence of a conic helical liquid crystalline structure in cylindrical microcavities

Abstract

Optical activity has been measured for cholesteric (Ch), twisted nematic (N*) and ferroelectric (S*_c) substances confined in cylindrical channels of anodic oxidized aluminium (Anopore membranes). ¹H and ¹³CNMR studies of the adsorbed N* phase in combination with measurements of the rotary power suggest a conic helical director field in the pores, as in a common S*_c structure, with the helical axes oriented along the cylindrical channels and the helicoidally ordered local directors on average being inclined at an angle θ < 90° to the cylinder axes. Supposing the validity of the de Vries formula, the sign and magnitude of the optical activity in Anopore indicate a change in birefringence and pitch with respect to the bulk sample.