(744h) Thermochromic Fibers Via Electrospinning and in Situ Phase Separation

Cholesteryl ester liquid crystals are a class of unique soft materials with thermochromic properties arising from their helical structure with a temperature-dependent pitch length. Near the mesophase transition temperature, the liquid crystal first reflects blue light (λ = 450 nm) at relatively short pitch lengths. As the temperature decreases, the wavelength reflected shifts to the red end of the spectrum (λ = 760 nm) due to the increase in pitch length. Such materials have been used in thermal mapping and analysis in medical, industrial, and engineering applications. Electrospinning is a useful approach to incorporate such functional additives into fibers. In this work, we aim to achieve thermochromic fibers in a single-step, single nozzle electrospinning process using solvent induced phase separation. Specifically, we blend the liquid crystal with spinnable polymer solutions (one-phase). During the fiber spinning process, as the solvent evaporates and the polymer concentration increases, phase separation of the liquid crystal will occur by spinodal decomposition or nucleation and growth process. Three polymer systems were examined with chloroform as the solvent: polystyrene (PS), polyethylene oxide (PEO), and polycaprolactone (PCL). The fibers were analyzed using polarized light microscopy (PLM) on a temperature-controlled stage. All of the blend systems formed fibers with fiber diameters ~15-30 microns depending on the polymer. Liquid crystal loadings (mass of LC/(mass of LC + mass of polymer)) between 60 and 97% could be achieved. These results indicate the liquid crystal did not disrupt the polymer entanglement required for fiber formation. Interestingly, the liquid crystal containing fibers spun from PEO and PCL produced thermochromic fibers with a core-shell structure (liquid crystal core/polymer shell) whereas the fibers spun from PS were not thermochromic. Thus, polymer-liquid crystal compatibility is an important consideration to achieve phase separation and thermochromic fibers.