Order parameter measurements from the Kossel diagrams of the liquid-crystal blue phases.

Abstract

Scalar order parameter measurements of the liquid crystal blue phase II (BPII), taken using the Kossel diagram technique, are presented. The temperature dependence of the order parameter is found to follow a curve predicted by the Landau theory. The order parameter data, derived from the diffracted light intensity, are normalized such that the fitted theoretical temperature dependence has a value of unity at a temperature of 0 K, representing perfect order. This normalized order parameter is found to be approximately 0.1 within the blue phase. The theory of the temperature dependence of the blue phase order parameter is summarized, together with the measurement technique employed. The measurements were made possible by use of a high-resolution charge-coupled-device camera, frame grabber, and image-analysis computer software to capture the Kossel diagram images. Also, a high-stability temperature controller and reflection microscope were used.