Aerogel fibers, the simultaneous embodiment of aerogel 3D network and fibrous geometry, have shown great advantages over natural and synthetic fibers in thermal insulation. However, as a fast gelation to ensure aerogel fiber spinning generally induces rapid local clustering of precursor particles (i.e., phase separation) and unavoidably results in nontransparency and nonuniformity in the gel state, a severe challenge remains in remedying the spinning to make transparent aerogel fibers come true. Herein, we report a reaction spinning toward highly porous silica aerogel fibers, where the Brownian motion (i.e., diffusion) of colloidal particles is hampered during spinning to allow the maintaining of the fiber shape, while a rapid gelation reaction is activated by concentrated ammonia to solidify the fiber. The aggregation degree of the primary particles can be precisely controlled by pH-dependent hydrolyzation, and thus, the final aerogel fiber can be either transparent or opaque, as dominated by Rayleigh or Mie scattering. The resulting transparent silica aerogel fibers with low density, high specific surface area, and flexibility can inherit advanced features including excellent thermal insulation, wide temperature stability, and optional hydrophobic functionalization and, thus, be suitable for wearable applications.
Keywords: multifunctional; reaction spinning; silica aerogel fiber; sol−gel process; transparent.