Janus Aramid Nanofiber Aerogels with Orientation-Switchable Solar Heating and Thermal Shielding

Orientation-switchable thermal-management materials that can reversibly alternate between solar-heating and thermal-shielding modes are highly desirable for reducing energy consumption and enhancing thermal protection. Herein, a Janus aramid nanofiber/poly(amic acid)-aramid nanofiber/titanium carbide (ANF/PAA-ANF/TiC; denoted AP-AT) bilayer aerogel was fabricated through directional freezing and a sol–gel process. The aerogel integrates a thermally insulating ANF/PAA layer composed of a hierarchical nanoporous nanofiber network with an ANF/TiC layer containing uniformly dispersed TiC nanosheets for efficient photothermal conversion and heat transport. Owing to this asymmetric architecture, the bilayer aerogel exhibits orientation-dependent heat transfer and an asymmetric photothermal response, enabling reversible switching between heating and thermal-shielding modes by changing the light-facing surface. The resulting aerogel exhibits an ultralow density of 0.089 g cm –3, thermal stability up to 500 °C, and a high compressive strength of 438.8 kPa. When the AP side faces a 200 °C hot plate, a temperature difference of approximately 100 °C is maintained across the aerogel, demonstrating its excellent thermal-insulation capability. Under 1000 W m –2 irradiation, the AT-facing configuration increases the temperature of the aerogel-covered region to 106.2 °C, whereas the AP-facing configuration limits it to 45 °C. Outdoor model-house tests further confirm the summer thermal-shielding and winter solar-heating capabilities of the AP-AT aerogel, highlighting its potential as a zero-energy, orientation-switchable thermal-management material. These results establish nanoengineered Janus aerogels as promising nanostructured platforms for adaptive thermal management and thermal-protection applications.