Elasticity of the blue phases of cholesteric liquid crystals.

Normal shear modes of axial symmetry were excited in polycrystalline samples of blue phases. An average shear modulus, E, of blue phases is determined (for the first time) from the frequencies of these modes which are found to be linear in temperature. Measuring the blue phase lattice constant, a, we deduce that K = Ea(2) is the order of magnitude of a Frank constant for cholesteric liquid crystals.