Influence of metal oxide nanoparticles on morphological, structural, rheological and conductive properties of mulberry silk fibroin nanocomposite solutions

This paper highlights about the effect of metal oxide nanoparticles on rheological and conductive properties of silk fibroin (SF) solution. Silk fibroin nanocomposite solutions are prepared using formic acid with the incorporation of metal oxide nanoparticles such as zinc oxide (ZnO), copper oxide (CuO) and, titanium dioxide (Ti0 2 ) in formic acid. Even distribution of metal oxide nanoparticles in silk fibroin solutions are observed through HRTEM. The addition of metal oxide nanoparticles to silk fibroin solution suppressed the 1 sheet conformation and enhanced the random coil conformation as confirmed by Fourier transform infrared spectroscopy. The steady shear analysis showed shear-thinning behavior of silk nanocomposite solutions and are found to be highly influenced by the shear rates. The viscosities of silk fibroin solutions are reduced from 5407 mPa s to 316, 367, and 709 mPa s, on the addition of ZnO, CuO, and TiO2 nanoparticles, respectively at a low shear rate of 0.1 s(-1). An oscillatory shear rheology test has been performed to evaluate the dynamics of the viscoelastic behavior of nanocomposite solutions. Silk fibroin/CuO solution is found to be frequency independent as analyzed in oscillatory sweep measurement. In a creep recovery test, pure silk fibroin solution showed delayed elasticity while nanocomposite solutions showed ideal viscous behavior. Rotational (constant low-high-low) shear has been applied to study the structure recovery test. Metal oxide nanoparticles brought better structure recovery in SF nanocomposite solutions. SF/metal oxide nanocomposite solutions show higher conductivity compared to pure silk fibroin solution.