A BODY-CENTERED CUBIC STRUCTURE FOR THE CHOLESTERIC BLUE PHASE

Using Landau theory, possible structures that can occur in chiral liquid crystals when the isotropic phase becomes thermodynamically unstable are analyzed. It is shown that the transition may be to a liquid crystal phase having a body-centered cubic (1432) structure rather than to the usual cholesteric (helicoidal) phase when the coefficient of the cubic term in the free energy is sufficiently small with respect to that of the chiral term. It is conjectured that this bcc structure characterizes the cholesteric blue phase. Arguments supporting this suggestion as well as the difficulties it presents are discussed.