Gradient assembly of alginic acid/quaternary chitosan into biomimetic hidden nanoporous textiles for thermal management

Hidden pores (including compact shell and porous core pores) occur naturally in polar animals' feathers/fur, and they show exceptional capability for thermal insulation. The facile implementation of such an architecture in macroscopic fibers is challenging. In this work, gradient assembly is developed to prepare biological hidden nanoporous fibers (average aperture, ~80 nm). Namely, a weak polyanion (alginic acid) and a polycation (quaternary chitosan) were dissolved in dimethyl sulphoxide (the anion charge of alginic acid was largely shielded) and then spun to ethanol/water/ammonia solution, whereby ammonia triggered the polymer assembly from the shell to the core. This presents an efficient process in 20 min, which is in stark contrast to tedious freeze-spinning or template methods. The as-prepared green textiles featuring much lower thermally conductivity (0.033 W m-1 K-1) compared with the conventional microporous/compact fibers, as well as robust mechanical strength and enhanced solar/electric-heat-harvesting properties, holding great potential to replace the unsustainable animal products.