Emerging polymer ferroelectrics with liquid crystalline order

For liquid crystals (LCs) and liquid crystalline polymers (LCPs), a chiral smectic C (SmC*) phase has been mandatory for breaking the symmetry and achieving ferroelectricity. However, this SmC* phase leads to rather low spontaneous polarization (P_s, 0.1–5 mC/m²), which has limited their usage in various electronic and electro-optical applications. In this mini-review, we highlight three new types of ferroelectric LCPs with high P_s values reported in the last decade. The first system refers to the ferroelectric nematic LCs and LCPs. The large dipole moment (>9 Debye or D) and oblique molecular shape induce a polar packing of calamitic nematics. The P_s can reach as high as 40 mC/m². The second example is a ferroelectric supramolecular LCP, in which the highly polar cyano groups in the core lead to a polar structure of the hexagonal columnar phase after electric poling. The P_s can reach ∼ 20 mC/m². The third system utilizes highly dipolar sulfonyl groups (dipole moment ∼4.5 D) in the side chains of mesogen-free comb-shaped LCPs. By combining finely tuned dipolar interactions and mobile LC order, these mesogen-free comb-like LCPs have shown good potential for ferroelectricity with high P_s. These ferroelectric LCPs with high P_s will enable new electronic and electro-optical applications in the future.