Synthesis and Characterization of Polymeric Nanofibers Templated Along Topological Defects in Ultrathin Liquid Crystalline Film

Formation of point defects, line disclinations and vortices are frequent in liquid crystalline materials, however application of these charged topological defects to synthesize materials has been rarely explored. In this work we have utilized substrate supported spin coated ultrathin E7 liquid crystal (LC) film (nematic) as a template to guide synthesis of nanofibers along the defect lines using chemical vapor polymerization (CVP) of [2.2]Paracyclophane based monomers. Such defects take on significant prominence for our system (60-300 nm LC films) because of the higher number density of defects in ultrathin films even after time-dependent annihilation of defects during the polymerization time. We predict that the polymerization would proceed exactly along the defect lines and to avoid artifacts such as changes in the nanofiber orientation after templating, critical point drying (CPD) has been used for removal of the LC phase. We have used polarizing optical microscope to characterize defect structures which allows for direct observation of darker lines or brushes in mixed LC/nanofiber phases (prior to LC removal3) and compared with the scanning electron microscope (SEM) images of the nanofibers to confirm that the defect structures get templated by the CVP process. We have observed that these distinctly identifiable short nanofibers can map 3-dimensional space of defect lines which shows presence of all different kind of LC defects including s = ±1, ±1/2 that appear to align with mathematically predicted defect patterns. We believe, understanding the nature and structure of LC defects will pave the path towards understanding of inducible defects, such as those created by particles immersed in a LC phase and how particle-loaded LC templating phases can be leveraged to design defects that template novel nanofiber patterns during CVD polymerization.