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 (Ps, 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 Ps 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 Ps 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 Ps 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 Ps. These ferroelectric LCPs with high Ps will enable new electronic and electro-optical applications in the future.