HIGH-PRESSURE OPTICAL STUDIES OF THE CHIRALITY AND PHASE-BEHAVIOR OF LIQUID-CRYSTALLINE BLUE PHASES

The blue phase (BP) polymorphism of chiral S-(+)-4'-(2-methylbutyl)phe nyl-4-decyloxy benzoate (CE6) and S-(+)-4'-(2-methylbutyl)phenyl-4-dod ecyloxy benzoate (CE7) was studied at elevated transition pressures up to 280 MPa using optical activity measurements. The increased density causes an increase in phase chirality which in the case of CE6 manife sts itself in the disappearance of BP II (BP I-BP II-BP III triple poi nt) and in the case of CE7 in the appearance of BP II. At atmospheric pressure, CE6 exhibits BP I, BP II and BP III, while CE7 only possesse s BP I. This pressure behaviour of CE6 and CE7 is contrary to that of cholesteryl nonanoate, which has been investigated previously. This re sult is particularly interesting when discussed in connection with the effect of elongation of the terminal n-alkylcarboxy chain of the chol esteryl n-alkanoates and of the terminal n-alkyloxy chain in the homol ogous series to which CE6 and CE7 belong. In the first case the phase chirality increases; in the second case it decreases. Since CE6 shows an obvious pretransitional optical activity in its isotropic liquid ph ase, pretransition and BP phase behaviour could be compared with each other at elevated transition pressures and temperatures. For those tra nsition pressures or temperatures where anomalies in the BP phase beha viour occur, anomalies in the pretransition behaviour are also observe d.