A simple method to measure the twist elastic constant of a nematic liquid crystal

We demonstrate a simple method for measuring the twist elastic constant (K22) of a nematic liquid crystal (LC). By adding some chiral dopant to an LC host, the LC directors rotate 180° in a homogeneous cell, which is known as 180° super-twisted nematic (STN) cell. By preparing two such STN cells with different chiral concentrations and measuring their Fréedericksz threshold voltages, we can obtain the K22 and helical twisting power simultaneously. In the whole process, there is no need to measure the pitch length. Our obtained K22 values agree well with those reported by using other methods.