Self-assembled, optically responsive nematic liquid crystal/polymer core-shell fibers: Formation and characterization

We report here the formation and structural characterization of optically responsive, highly birefringent electrospun nematic liquid crystal (LC) microfibers. The LC microfibers are electrospun from a solution of polylactic acid (PLA) and low molecular weight 4-pentyl-4'-cyanobiphenyl (5CB) in chloroform/acetone solvent. In the electrospinning process, the low molecular weight 5CB phase-separates and self-assembles to form a planarly aligned nematic core within a PLA shell. The solubility limit of 5CB in PLA and the degree of phase separation of LC in the 5CB/PLA core/sheath fibers is determined using the phase transition enthalpies associated with LC and polymer components. Structural analysis revealed that the LC core and dissolved LC in the fibers promote the formation of the α-form of PLA crystals and increase the degree of crystallinity of the PLA shell in 5CB/PLA fibers from 6.6% to 52%. Competition between 5CB droplet formation and PLA fiber formation is observed as a function of spinning solution composition and applied electrospinning voltage. Alignment of the 5CB within the PLA core is confirmed by polarizing optical microscopy.