Nanoindentation, nanoscratch, and nanotensile testing of poly(vinylidene fluoride)-polyhedral oligomeric silsesquioxane nanocomposites

摘要

Nanocomposites composed of a poly(vinylidene fluoride)(PVDF)matrix and 0, 3, 5, and 8 wt % fluoropropyl polyhedral oligomeric silsesquioxane(FP-POSS)were prepared by using the solvent evaporation method. The morphology and the crystalline phase of the nanocomposites were investigated by digital microscopy, scanning probe microscopy, X-ray diffractometer, and Fourier transform infrared spectroscopy. FP-POSS acted as nucleating agent in PVDF matrix. A small content of FP-POSS resulted in an incomplete nucleation of PVDF and generated bigger spherical particles, whereas higher contents led to a complete nucleation and formed more separate and less-crosslinked particles. Nanoindentation, nanoscratch, and nanotensile tests were carried out to study the influence of different contents of FP-POSS on the key static and dynamic mechanical properties of different systems. The nanocomposite with 3 wt % FP-POSS was found to possess enhanced elastic properties and hardness. However, with the increase of the FP-POSS content, the elastic modulus and hardness were found to decrease, and the improvement on stiffness was negative at contents of 5 and 8 wt %. Compared with neat PVDF, the scratch resistance of the PVDF/FP-POSS nanocomposites was decreased due to a rougher surface derived from the bigger spherulites. Nanotensile testing results showed both the stiffness and toughness of PVDF-FP _(3%)were enhanced and further additions of FP-POSS brought dramatic enhancements in toughness while associated with a decline in stiffness. Dynamical mechanical properties indicated the viscosity of the nanocomposites increased with the increasing FP-POSS contents.