Preparation And Properties Of Silica Nanotube/Polyimide Nanocomposite Films

Polyimide (PI) is a kind of high performance polymer material with outstanding mechanical, thermal and electrical properties, and has been widely used in the fields of aerospace, microelectronic and cryogenic superconducting technology. With the rapid development of modern electronic technology etc, higher performance polyimide films are required. Nowadays many research efforts have been and are still being made on preparing polyimide nanocomposites to enhance the properties of polyimide films by adding nanomaterials.In this paper, silica nanotubes were synthesized from tetraethyl orthosilicate (TEOS) using ammonium tartrate as template, and then silica nanotube/polyimide nanocomposite films with different content were prepared by in-sit polymerization method. Silica nanotubes and nanocomposite films were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X-ray analysis (EDX), powder X-ray diffraction (XRD), Fourier transfer infrared spectra (FTIR) and ultraviolet-visible (UV-Vis). Then, the mechanical properties (tensile strength, elastic modulus, elongation at break and tearing strength), thermal properties (thermal stability, glass transition temperature Tg, thermal diffusivity and coefficient of thermal expansion) and electric properties (volume resistivity, surface resistivity, dielectric constant and loss factor) of nanocomposite films were studied.The results showed that the product yield of silica nanotubes was high and the silica nanotubes had large aspect ratios. It was shown that the morphology and the yield were sensitive to TEOS addition time, aging time after TEOS addition and ammonia concentration. The tensile strength, tearing strength and elongation at break of the nanocomposite films with proper silica nanotube content were improved simultaneously. As the silica nanotube content increased, the transparency of nanocomposite films consistently decreased. On the other hand, the glass transition temperature Tg, the volume resistivity and the surface resistivity first increased to a maximum and then decreased while the dielectric constant and the loss factor first decreased to a minimum and then increased with the increase of silica content. Addition of silica nanotubes significantly decreased the coefficient of thermal expansion of nanocomposite films and substantially improved the temperature and frequency stability of the dielectric constant and the loss factor.