Multiple Phase Structures and Enhanced Dielectric Properties of Side-Chain Liquid Crystalline Polymer Containing Unique Biaxial Mesogen with Large Dipole Moment
Zi-Fan Yang,
Le Zhou,
Wei Xia,
Lan-Ying Zhang,
Huai Yang,
Yang Shen,
Shuang Yang,
Er-Qiang Chen
Affiliations
Zi-Fan Yang
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, PR China
Le Zhou
School of Materials Science and Engineering, Tsinghua University, Beijing, 100084, PR China
Wei Xia
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, PR China
Lan-Ying Zhang
Beijing Advanced Innovation Center for Materials Genome Engineering & School of Materials Science and Engineering, Peking University, Beijing 100871, PR China
Huai Yang
Beijing Advanced Innovation Center for Materials Genome Engineering & School of Materials Science and Engineering, Peking University, Beijing 100871, PR China
Yang Shen
School of Materials Science and Engineering, Tsinghua University, Beijing, 100084, PR China
Shuang Yang
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, PR China; Corresponding authors.
Er-Qiang Chen
Beijing National Laboratory for Molecular Sciences, Key Laboratory of Polymer Chemistry and Physics of Ministry of Education, Center for Soft Matter Science and Engineering, College of Chemistry and Molecular Engineering, Peking University, Beijing, 100871, PR China; Corresponding authors.
To achieve all-organic polymer with high dielectric performances, we have designed a novel side-chain liquid crystalline polymer (P7) with strong polar mesogen of (Z)-4-(2-cyano-2-phenylvinyl)benzonitrile (CSCN) attached to polycyclooctene backbone. The bis-cyano-substituted CSCN is board-shaped and exhibits a large dipole moment (8.54 D) which tilts ∼34.2° away from its molecular long axis. Consequently, CSCN shows unique dual molecular anisotropy: one from biaxial shape anisotropy and the other from polarization anisotropy. The complex phase behaviors of P7 were investigated employing mainly the techniques of differential scanning calorimetry and X-ray diffraction. Four liquid crystal (LC) phases are identified as K0, K1, K2 and K3, which are SmA, highly-ordered biaxial SmA, B5-like and B7-like, respectively, with the thermal stability increased in sequence. The experimental results indicate that the different LC phases are arisen from the competition and balance between π-π stacking and dipole-dipole interaction. While the face-to-face π-π stacking is dominant in K0 and K1, optimizing the dipole-dipole interaction causes the CSCN mesogens within the smectic layer to tilt and rotate, resulting in K2 and K3. We further investigated the dielectric properties of P7 films using polarization-electric field loops test. The dielectric constant (εr) of P7 is found to be LC structure dependent, which is increased when the LC phase is varied from K0 to K3. With an average εr of 9.7 achieved in K3 and the low dielectric loss (tan δ = 0.001), P7 film offers a promising material in advanced applications like energy storage and electronic devices.
