Hollowing Out Nanofibers for Enhanced Visual Brightness and More Effective Solar Heating

The temperature rise of a solar-heating textile is controlled by both generation and dissipation of heat. However, current designs mainly focus on increasing light absorption to generate more heat, often darkening the material while leaving thermal management largely overlooked. Herein, hollowing the nanofibers in a nonwoven mat produces a counterintuitive "brighter-yet-hotter" advantage over their solid (core-shell) counterparts. The polyacrylonitrile/polypyrrole double-shelled tubular nanofibers are fabricated by selectively removing the poly(ε-caprolactone) core from core-shell nanofibers. At outer and inner diameters of about 320 and 160 nm, the hollow nanofibers enhance backscattering in the visible range, making the mat brighter. Under 1 sun irradiation, the mat of hollow nanofibers shows a temperature rise of 28°C, which is 12% greater than that of the paired solid counterpart. Thermal modeling indicates that the higher temperature rise originates from the internal channels, which disrupt heat propagation across the fibers and lower the rate of heat dissipation. Side-by-side comparisons under simulated and outdoor sunlight show that the higher-temperature region consistently appears on the mat of hollow nanofibers. This work highlights the promise of hollow nanofibers as a structural platform for optical and thermal management in solar-heating textiles.