Polyimide-surface-modified silica tubes: Preparation and cryogenic properties

The silica tubes were synthesized by template self-assembly from D,L-tartaric acid and hydrolysis of tetraethoxysilane (TEOS), and their surfaces were modified by a 3-aminopropyltriethoxysilane coupling agent. Thereafter, a series of polyimide (PI)-surface modified silica tube (ST) hybrid films was prepared from PMDA-ODA in N,N-dimethylacetamide as a solvent using an in situ polymerization process combined with ultrasonic dispersion and multistep curing. The resulting silica tubes and the hybrid films were characterized using XRD, SEM, TEM, FTIR, and UV-vis. The cryogenic mechanical properties at 77 K and dynamic mechanical properties of the hybrid films were studied. The results indicated that the strength, modulus, and failure strain of the hybrid films were all increased compared with those of the pure PI film when the silica tube content was at 1-3 wt %. The cryogenic tensile strength and modulus were generally higher than those at room temperature, whereas the cryogenic failure strain was lower than that at room temperature. The elastic modulus of the hybrid films exhibited a monotonically increasing trend. The cryogenic failure strain of hybrid films with 1-3 wt % silica tube contents was greater than with 15 wt %, indicating a good ductility at 77 K. The glass-transition temperature of the hybrid films increased with the increase in silica tube content.