Fabrication of patterned liquid crystalline polymer nanofibers using electric field and its applications

Abstract

Many researchers have endeavored to replicate nanoscopic or microscopic structures of natural fibers at the nanometer or micrometer scale to obtain valuable functions. One essential factor in this replication is controlling the orientation of synthetic fiber bundles. Various properties, such as mechanical strength, wettability, and heat transfer, can be enhanced by controlling the alignment of fiber bundles. Polymers are promising materials for producing such well-controlled fibers because of their molecular flexibility, mechanical and chemical durability, and ease of synthesis. However, the high chemical stability of polymers makes it challenging to manage their orientation, as it takes a lot of energy and time. Thus, an "in-situ" method that allows for orientational ordering during synthesis can be a practical solution. Liquid crystal (LC) templating polymerization is a method that utilizes liquid crystal compounds as templates to guide the polymerization of monomers into aligned structures. LCs have a long-range order, and their orientation can be precisely controlled using various techniques such as surface treatment, spatial confinement effects, and external fields. Considering these characteristics, utilizing LCs as templates allows for the easy production of polymer fibers that are uniformly oriented and have specific shapes. When the concentration of the monomer is substantially lower than the concentration of LC, the resulting polymer network exhibits a fibrous morphology. These fibers can exhibit various intriguing physical properties, including birefringence, polarizability, and chirality. Developing techniques to organize these fibers into arrays is crucial to achieving customized properties and yielding novel properties such as superhydrophobicity, adhesive, anisotropic wetting, and enhanced thermal conductivity. In this study, patterned polymer nanofibers were fabricated using a small molecular-weight liquid crystal (LC) and reactive mesogens (RMs) under controlled electric fields in which defect arrays are generated depending on the electrode configuration. For this, the AC electric field with interdigitated electrodes is used to develop versatile defect structures of the LC phase. Hydrophobic LC network (LCN) fibers exhibiting porous morphologies have been made by removing the LC part after the polymerization of RM. The resulting LCN fibers show a surface tension reduction characteristic compared to the neat RM film and a sticky characteristic with the water droplet, suggesting a facile way to fabricate the hydrophobic surface that can be used in microdroplet transport.