Smectic C Self-Assembly in Mesogen-Free Liquid Crystalline Chiral Polyethers with Sulfonylated Methyl-Branched Side Chains

To realize advanced electrical applications for ferroelectric liquid crystalline polymers, high spontaneous polarization (P-s) is highly desired. However, current ferroelectric liquid crystalline polymers usually exhibit a low P-s. In this work, mesogen-free, chiral polyethers containing sulfonylated methyl-branched alkyl side chains with a -(CH2)(3)O- spacer between the sulfonyl and the branched alkyl groups are designed and synthesized. In contrast to the linear n-alkyl side chains, the methyl-branched alkyl side chains induce chain tilting in the smectic layers. When double chirality exists in both the main chain and the side chains, a crystalline structure is observed after mechanical stretching. Intriguingly, when single chirality exists in either the backbone or the side chains, a liquid crystalline smectic C phase is obtained. The electric displacement-electric field study, however, does not show typical ferroelectric switching, although the dielectric constants are relatively high for these liquid crystalline polymers. This is likely because the dipole-dipole interactions among neighboring sulfonyl groups along the main chain are so strong that the ferroelectric switching is hindered in the samples. For the future work, it is desired to weaken the dipole-dipole interaction to achieve ferroelectricity in these mesogen-free liquid crystalline polymers.

Automated summary

In order to achieve advanced electrical applications for ferroelectric liquid crystalline polymers, researchers designed and synthesized a new type of polyether with sulfonylated methyl-branched alkyl side chains. They found that a crystalline structure is observed when both the main chain and the side chains have double chirality, while a liquid crystalline smectic C phase is obtained when either the backbone or the side chains have single chirality. However, the electric displacement-electric field study did not show typical ferroelectric switching, likely due to the strong dipole-dipole interactions among neighboring sulfonyl groups hindering the ferroelectric switching.