Blue phases of cholesteryl nonanoate

Abstract

The transformation on heating of an ordinary (helical) cholesteric liquid crystal (CHOL) into the isotropic phase (ISO) often occurs via a number of intermediate "blue" phases. We find the following scheme of phase transitions in cholesteryl nonanoate: $\mathrm{CHOL}\underset{91.35}{\ensuremath{\rightarrow}}\mathrm{BPI}\underset{91.76}{\ensuremath{\rightarrow}}\mathrm{BPII}\underset{91.84}{\ensuremath{\rightarrow}}\mathrm{BPIII}\underset{91.95}{\ensuremath{\rightarrow}}\mathrm{ISO}$. Here BPI, BPII, and BPIII indicate three distinct, thermodynamically stable phases; transition temperatures are in \ifmmode^\circ\else\textdegree\fi{}C. From observations of supercooling and coexistence, we conclude that all these transformations are first order, except possibly the BPIII\ensuremath{\rightarrow}ISO, the character of which remains in doubt. A similar behavior is found in cholesteryl myristate and in a mixture of cholesteryl nonanoate and cholesteryl chloride. A few observations having a bearing on the structure of the blue phases are reported.