Liquid Single Crystals of Cholesteric Blue Phases

Liquid single crystals of cholesteric “Blue Phases” (BP) have been prepared and observed by polarizing microscopy. They exhibit a quadratic size without any exception. At the phase transition BP II → BP I a cross-hatching occurs, diagonal to the square sides, indicating a four-fold crystal symmetry. The observed habitus of the BP single crystals clearly evidences a cubic structure of the molecular arrangement. Possible space groups are discussed.