In situ measurements of twist and bend elastic constants in the oblique helicoidal cholesteric

Unique electro-optical properties of the oblique helicoidal cholesteric (ChOH) stem from its heliconical director structure. An applied electric field preserves the single-harmonic modulation of the director while tuning the ChOH period and the corresponding Bragg-peak wavelength within a broad spectral range. We use the response of ChOH to the electric field to measure the elastic constants of twist K-22 and bend K33 directly in the cholesteric phase. The temperature dependencies of K-22 and K-33 allow us to determine the range of the electric tunability of the ChOH pitch and the heliconical angle. The data are important for understanding how molecular composition and chirality influence macroscopic elastic properties of the chiral liquid crystals and for the development of ChOH-based optical devices.