Rapid synthesis of polymer-silica hybrid nanofibers by biomimetic mineralization

Biomimetic formation of silica from polyamines such as poly(ethylene imine) (PEI), inspired by the proteins found in diatoms and sponges, has been actively investigated recently as a potential route to silica formation compared to the conventional sol-gel process. We report silica formation onto nanofibers of PEI blended with poly(vinyl pyrrolidone) (PVP) obtained via electrospinning of their 50:50(w/w) blend. The active component, PEI, catalyzes rapid silica formation, within minutes, upon immersion of the PEI/PVP nanofibers in silica precursor tetramethylorthosilicate (TMOS). The silica formation in nanofibers was then investigated by scanning electron microscopy (SEM), Energy Dispersive X-ray analysis (EDX), differential scanning calorimetry (DSC), thermo-gravimetric analysis (TGA) and Fourier-transform infra-red (FTIR) spectroscopy. The silica content in the PEI/PVP nanofibers could be controlled by pre-treatment of the fibers at different conditions of relative humidity prior to the silicification. Fibers exposed at higher (80%) relative humidity led to higher inorganic (silica) content compared to those exposed to relative dry conditions (<20% relative humidity). Calcination of the fibers indicated that silicification proceeded across the whole fiber cross-section that consisted of nano-structured silica. Such a simple route to rapid formation of organic-inorganic hybrid nanofibers could have applications ranging from catalysis to tissue engineering, and nanocomposites in general.