Structure-induced enhancement of thermal conductivities in electrospun polymer nanofibers

Abstract

Polymers that are thermally insulating in bulk forms have been found to exhibit higher thermal conductivities when stretched under tension. This enhanced heat transport performance is believed to arise from the orientational alignment of the polymer chains induced by tensile stretching. In this work, a novel high-sensitivity micro-device platform was employed to determine the axial thermal conductivity of individual Nylon-11 polymer nanofibers fabricated by electrospinning and post-stretching. Their thermal conductivity showed a correlation with the crystalline morphology measured by high-resolution wide-angle X-ray scattering. The relationship between the nanofiber internal structures and thermal conductivities could provide insights into the understanding of phonon transport mechanisms in polymeric systems and also guide future development of the fabrication and control of polymer nanofibers with extraordinary thermal performance and other desired properties.

Thermal Transport in Conductive Polymer–Based Materials

“…More recently, Rojo et al demonstrate an increase of thermal conductivity in polymeric P3HT nanowire with different diameters by crystal orientation, similar to the observation in Nylon‐11 nanofibers . This work reports the measurement of 3ω scanning thermal microscopy (SThM) in P3HT nanowire fabricated by anodic aluminum oxide template ( Figure a–c).…”

“…Thermal bridge method is very successful in measuring thermal conductivity of suspended single polymer fibers and films . However, there are limitations.…”

Thermal Conductivity of Polymers and Their Nanocomposites

“…This diameter‐dependence behaves quite differently from inorganic nanowires where the thermal conductivity reduces with the decreasing diameter due to surface scattering. This indicates that the enhancement observed is due to structural changes, which was confirmed by high‐resolution wide‐angle X‐ray scattering . In terms of the relatively lower thermal conductivity observed in Nylon‐11 compared with that in the PE nanofibers, the degree of crystallinity of Nylon‐11 is only 35%–40% compared to that of 80%–90% in PE, apart from the fact that the intrinsic Young's modulus in Nylon (≈25 GPa) is one order of magnitude smaller than that in PE (≈240 GPa) .…”

Piezoelectric Nylon‐11 Nanowire Arrays Grown by Template Wetting for Vibrational Energy Harvesting Applications

“…Among odd-numbered Nylons, Nylon-11 (polyamide-11 = [C11H21ON]n) exhibits piezoelectric and ferroelectric properties that are comparable to PVDF at room temperature. [32][33][34][35] Typically, Nylon-11 exhibits five crystalline modifications, including triclinic α and pseudo-hexagonal γ phases, which have different dipole densities and orientation. [36,37] The high piezoelectricity in Nylon-11 is attributed to its polar crystal structure (γ form), although other configurations may also lead to piezoelectric behavior (see Supporting Information S1).…”