The responsive behaviors of graphene oxide (GO)-based films under external straining make it possible to develop man-made adaptive materials. Some researches have suggested that GO nanosheet alignment plays important roles in dynamic stiffening behaviors; however, the effects of inter-sheet interactions have not been thoroughly investigated. In this study, the GO interlayer interactions are tuned by third components, including hydrophilic nanofumed silica (SiO 2 ) nanoparticles, chemically modified SiO 2 nanoparticles, and waterborne polyurethane particles, and their stiffening behaviors and structural changes during periodic external straining are systematically characterized. During external dynamic straining, the storage modules ( E ′) of GO-based composite films increases up to 55.5% after 12 h. It is observed that the interlayer adhesion is important for the self-stiffening behaviors of GO-based films. The interaction types, including reversible H-bonding and non-reversible chemical bonding, play different roles on the structural-responsive behaviors. During external dynamic straining, the interlayer contact between GO nanosheets is improved, and the higher interlayer adhesion leads to improved mechanical properties, instead of the improvement of GO sheet orientation. These findings are helpful to better understand the responsive behaviors of nanomaterials as well as to develop new types of man-made adaptive materials.
Sandwich structure of cubic (C) phase/monoclinic (M) phase/C phase was formed in 8% mol Y 2 O 3 partially stabilized HfO 2 (Hf 0.92 Y 0.08 O 1.96 , YSH8) samples which were produced by sintering of YSH8 green body cold pressed from nano-powders of C phase at 1500 °C. The geometry of the sandwich structure was approximately tailored by controlling the sintering time. The YSH8 samples with sandwich structure from nano-powders yielded fracture toughness of 2.1–2.4 MPa m 0.5 , which was about 33% higher than that of conventional YSH8 sample sintered from micron powders. Both the experimental results and numerical simulation indicated that the fracture toughness is closely related to the geometry of the sandwich structure.
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