Polarization competition and relaxation rotation in chiral doped ferroelectric nematic liquid crystal

Since the discovery of ferroelectric nematic liquid crystals (FNLCs), these materials have attracted considerable attention owing to their inherent spontaneous polarization and rapid electric field response characteristics. Recent studies on chiral ferroelectric nematic liquid crystal (CFNLC) also indicate that CFNLC has great application potential in fast electro-optical switching and phase modulation. In this study, two new FNLC topological structures were observed in different temperature ranges of CFNLC samples. With the decrease of temperature (138-210 °C), a cross-shaped structure was observed in CFNLC, which was very similar to the conformation observed in cholesteric liquid crystal. Upon further cooling (104-138 °C), the interplay between chiral elasticity and spontaneous polarization leads to the formation of cross-shaped multidomain structures. When a weak alternating current electric field is applied, driven by the cooperative competition among chiral twisting force, spontaneous polarization, and external electric field, the single domain molecular director rotates reversibly and continuously and spontaneously returns to the initial equilibrium state after removing the electric field (relaxation rotation). Afterward, the relaxation rotation behavior of CFNLC was simulated by establishing a model, and the results were in good agreement with our experimental results. Based on the mechanism of relaxation rotation, it is anticipated to realize an optical modulator with superior low driving voltage and high modulation speed. These findings suggest that CFNLC may serve as low-voltage electro-optical platforms for tunable polarization modulation and switching.