Electrostriction of the cholesteric blue phases BPI and BPII in mixtures with positive dielectric anisotropy

The electrostriction of the cubic blue phases was investigated in the well known mixture CB15/E9. The results for BPI prove that a decrease of the lattice constant in the field direction with increasing field strength can occur in a system with positive dielectric anisotropy. In agreement with recent theoretical considerations, all components of the electrostriction tensor for this mixture exhibit the opposite sign compared to systems with negative dielectric anisotropy.