Templated Silica Tubes with High Aspect Ratios as Effective Fillers for Enhancing the Overall Performance of Polyimide Films

Silica tubes (T-silica) with uniform size and large aspect ratios were synthesized by hydrolyzing tetraethyl orthosilicate using d, l -tartaric acid as a template. The prepared silica tubes have a diameter of about 200–400 nm and a length of about 40−100 µm; hence, their aspect ratios range from 100 to 500. The inner shape of the silica tubes is rectangular, and their wall thickness is 100–150 nm. T-silica/polyimide (PI) composite films were prepared from a solution of a PI precursor (polyamic acid) and silica tubes modified by a coupling agent (γ-aminopropyltriethoxy silane, KH-550). The overall performance including tensile strength, ductility, tearing strength, thermal expansion and diffusivity, and volume and surface resistivities of the T-silica/PI composite films were examined as a function of the T-silica content. It is interesting to note that the tensile strength and ductility have been simultaneously improved; tearing strength has also been enhanced; thermal expansion and diffusivity have been simultaneously decreased; and both volume and surface resistivities have been dramatically enhanced by the introduction of T-silica in proper amounts into the PI matrix. Moreover, the composite films containing silica tubes have low densities that range from 1.408 to 1.447 g/cm 3 . These suggest that templated silica tubes are very effective in enhancing the overall performance of the PI composite films that have a great potential to be used as electrical and thermal insulating materials in high tech areas such as aircraft and spacecraft manufacture and so forth, where high strength and ductility, high tearing strength, low thermal expansion and diffusivity, high resistivities, light weight, and so forth are desirable.