A Heat-Resistant Polyimide Nanofibrous Moisture Diode for Thermal-Insulating Protective Interlayers

Thermal-protective textile interlayers must block external heat without trapping perspiration next to the skin. This requirement is difficult to meet because low-thermal-conductivity structures favor heat shielding, whereas wettable and open fibrous networks are needed for rapid moisture release. Here we show a heat-resistant polyimide nanofibrous moisture diode that couples thermal insulation with directional liquid transport. The membrane is built from a hydrophobic ytterbium oxide/polyimide nanofiber membrane (Yb2O3/PI NFM) heat-shielding layer and a hydrophilic lithium chloride /polyimide nanofiber membrane (LiCl/PI NFM) capillary layer. The low thermal conductivity of the Yb2O3/PI layer limits through-thickness heat transfer, while the hydrophilic LiCl/PI layer, with its bimodal nano/submicron fibrous morphology, draws and spreads water after it crosses the hydrophobic side. This asymmetric wettability and pore architecture rectifies liquid transport from the hydrophobic Yb2O3/PI side toward the hydrophilic LiCl/PI side. The PI(2:2) bilayer, prepared using equal precursor-solution volumes, shows a 54 °C temperature difference on a 200 °C hot stage, a water-vapor transmission rate of 7854 g m−2 d−1 and a one-way transport index of 957.43% from a moisture-management test, indicating preferential liquid transport from the hydrophobic side toward the hydrophilic side, with flame cessation observed after separation from the ignition flame during a qualitative flame-exposure test. These findings support further exploration of PI nanofibrous membranes for thermal and moisture management in protective textile interlayers.