Research

The main research topic is to understand the physical properties and the electro-optical characteristics of blue phases. There are several subjects in our research group:

1. Effect of the physical parameters of the liquid crystals on the thermal stability of the BPs.

In this subject, we discuss the relation between the temperature range of the BPs and elastic constants, chirality and dielectric anisotropy of LC materials. In more than 30 different BP samples, the experimental evidence displays that the total temperature range of the BPs linearly depends on the elastic constants and the dielectric anisotropy of nemtaic hosts, but does not depend on the chirality of the chiral nematic mixtures. Smaller dielectric anisotropy can induce BPs in a wider temperature range. These experimental results can be explained by Defect theory and Landau theory.

2.Wide temperature range of BPIII and its electro-optical properties

Several theoretical models have been proposed to describe the structure of BPIII, such as an emulsion of cholesteric droplets in an isotropic matrix, the double twist model consisting of randomly orientated DTCs, the BPII-like cubic model containing a small simple cubic domain, and the quasicrystal model which is characterized by a locally icosahedral symmetry. However, to date, a suitable description of the BPIII structure has not been confirmed. Most experiments focus on studying BPI and BPII, as they are easier to observe and stabilize in a wider temperature range. Because the available temperature range of BPIII was limited to one or less Kelvin for many years, only a few papers present experimental observations of BPIII. The way to understand the structure of the BPIII is to widen the temperature range of it. From our experience, we found that a high solubility chiral dopant may be a key to widen the temperature range of the BPIII. Until now, the BPIII can be stabilized more than 20 C by choosing a suitable chiral dopant in our work.

By studying the reflection spectra of BPIII in a field, perpendicular to the substrate, we can know that the possible structure of BPIII is quite different from BPI or BPII. We also try to see the structure of BPIII directly from the FFTEM. This work is cooperation with LCMRC, CU at Boulder. The electro-optical response of BPIII by applying an in-plane field attracts us. In our preliminary observation, we find that the electro- optical response of BPIII can not only be explained by Kerr effect (which is usually be used to explain the EO behavior in BPs). We need to design more experiments to understand the effect of BPIII, such like transmission and reflection polarization, birefringence measurement, flexoelectric effect observations.