Probing the structure evolution/orientation induced by interaction between polyurethane segments and SiO2 surface in shape memory process

The effects of interactions between nano-SiO2 and polyurethane segments on structure and orientation behaviors in shape memory process have been systematically investigated. Polyurethane (PU)/nano-SiO2 composites were prepared by solution mixing in tetrahydrofuran (THF). The scanning electron microscopy (SEM) observation shows that nano-SiO2 particles are well dispersed in PU matrix. Besides the shape memory performance of pure PU is superior to that of PU/nano-SiO2 composite with 3 wt% filler content. It has been proved that the nano-SiO2 has some interaction with the segments of PU, affecting the orientation behaviors of polyurethane in both drawing and recovery process. In the drawing process, the hard segments at the domain interface and soft segments of PU-3% have a perpendicular direction at the small strain, and then possess a parallel orientation at larger deformation, whereas those of PU-0% orient positively from the beginning to the end. Moreover, the mobility of both soft and hard segments is retarded mostly by the nano-SiO2. In addition, differential scanning calorimetry (DSC) and wide-angle X-ray diffraction (WAXD) tests have also been done. The results indicate that crystallization is quite small influenced by the addition of nano-SiO2.