Topological Defects Induced by Air Inclusions in Ferroelectric Nematic Liquid Crystals with Ionic Doping

We report an experimental study on how topological defects induced by cylindrical air inclusions in the ferroelectric nematic liquid crystal RM734 are influenced by ionic doping, including an ionic surfactant and ionic polymer. Our results show that subtle differences in molecular structure can lead to distinct surface alignments and topological defects. The ionic surfactant induces a planar alignment, with two -1/2 line defects adhering to the cylindrical bubble surface. In contrast, the ionic polymer promotes homeotropic alignment, resulting in a -1 polar disclination around the cylindrical bubble. By numerical simulations, we verify that these topological defects are vertical lines with two dimensional polarization fields. These configurations differ from the boojums and hedgehog defects induced by air inclusions in nematic liquid crystals, highlighting the significant role of broken inversion symmetry.