Determination of helical twist in liquid crystals: Examples and terpenoids as chiral dopants

Helical twists exist in liquid crystals as a result of the addition of chiral dopants or boundary conditions and play a role in several liquid-crystal phenomena and devices. To date, various methodologies have been explored, albeit with varying degrees of precision and complexity, often resulting in the measurement of just one parameter, such as helical sense. However, a consensus on the optimal technique remains elusive. We developed a technique to determine the total twist angle and handedness of the twist by using optical transmission spectroscopy. We present the theoretical background and experimental technique and test it against some other results and results from data published elsewhere. Furthermore, we investigate the use of three naturally occurring terpenoid materials as chiral dopants for liquid crystals and determine the helical handedness using the spectroscopy method.