Optical rotatory dispersion measurements in the third cholesteric blue phase

Abstract

The results of optical rotatory dispersion (ORD) measurements in the third cholesteric blue phase (BP III) are reported for both pure compounds and mixtures. The spectra possess weak, broad, anomalous regions at short wavelength, the sign and wavelength dependence of which follows the sense and pitch of the cholesteric helix. A temperature-pitch phase diagram for the alkyl esters of cholesterol is presented which, together with the calorimetric measurements of others, indicates that the BP III---isotropic transition is in fact the liquid crystal to isotropic liquid transition. In addition, the ORD measurements reported here provide evidence for a BP III structure which lacks longrange periodic order.