Effects of Structural Ordering on the Thermal Diffusivity of Liquid-Crystalline Poly(ester imide) Nanofibers

Abstract

The development of polymer materials with high intrinsic thermal conductivity is essential for efficient heat dissipation in next-generation electronics. In this study, we report the fabrication and characterization of liquid-crystalline (LC) polyimide nanofibers (PI-NFs) designed to achieve a highly ordered internal structure. Highly aligned LC-PI-NFs were prepared via electrospinning of a poly(amic acid) precursor containing rigid phenyl benzoate mesogens and flexible dodecyl spacers, followed by stepwise thermal imidization. To further enhance molecular alignment, uniaxial tensile drawing was applied during the imidization process. Upon thermal imidization, wide-angle X-ray scattering (WAXS) revealed a phase transition from the initial smectic (Sm) A phase to a more ordered SmF phase. Furthermore, combined WAXS and small-angle X-ray scattering (SAXS) analyses suggested that uniaxial drawing enhances the ordering of the LC structure. Microscale temperature wave analysis demonstrated a positive correlation between the internal structural order and the thermal diffusivity along the fiber axis, which reached a value of 6.6 × 10–7 m2 s–1 (corresponding to a thermal conductivity of 1.0 W m–1 K–1) for the uniaxially drawn LC-PI-NFs. These results demonstrate that synergistically integrating LC phase behavior with processing-induced strain is a promising strategy for developing high-performance, thermally conductive polymer nanostructures.