Wood-Derived, Vertically Aligned, and Densely Interconnected 3D SiC Frameworks for Anisotropically Highly Thermoconductive Polymer Composites.

Construction of a vertically aligned and densely interconnected ordered 3D filler framework in a polymer matrix is a challenge to attain significant thermal conductivity (TC) enhancement efficiency. Fortunately, many biomaterials with unique microstructures can be found in nature. With inspiration from wood, artificial composites can be rationally designed to achieve desired properties. Herein, the authors report a facile and effective approach to fabricate anisotropic polymer composites by biotemplate ceramization technology and subsequent vacuum impregnation of epoxy resin. The hierarchical microstructure of wood is perfectly replicated in the cellular biomass derived SiC (bioSiC) framework by carbothermal reduction. Owing to the anisotropic architecture of bioSiC, the epoxy composite with vertically aligned dense SiC microchannels shows interesting properties, including a high TC (10.27 W m-1 K-1 ), a significant enhancement efficiency (259 per 1 vol% loading), an outstanding anisotropic TC ratio (5.77), an extremely low coefficient of linear thermal expansion (12.23 ppm K-1 ), a high flexural strength (222 MPa), and an excellent flame resistance. These results demonstrate that this approach is expected to open a new avenue for design and preparation of high performance thermal management materials to address the heat dissipation of modern electronics.

Synthesis and carbothermal nitridation mechanism of ultra-long single crystal α-Si3N4 nanobelts.

One-dimensional Si3N4 nanostructures are desirable for constructing nanoscale electric and optoelectronic devices due to their peculiar morphologies. Herein, a facile and environmentally friendly catalyst-free method is proposed to synthesize ultra-long single crystal α-Si3N4 nanobelts via carbothermal nitridation of carbon nanotubes at 1750 °C. The obtained α-Si3N4 nanobelts with a flat surface (thickness of ∼150 nm, length of several millimeters) exhibited an extremely high aspect ratio, perfect crystal structure, and high specific surface area of 7.34-10.09 m2 g-1. In addition, the width was increased from approximately 80 nm to 8 µm by increasing the holding time from 1 to 3 h. The nanobelt formation was governed by the vapor-solid (VS) reaction between SiO vapor, N2 and carbon nanotubes, and the vapor-vapor reaction between SiO, CO and N2. The former was responsible for the initial nucleation and successive base-growth of α-Si3N4 nanotubes. The latter additionally contributed to the nanorod and subsequent proto-nanobelt formation and to the growth of the nanobelts. During high-temperature annealing at 1750 °C, the original Si3N4 nanotubes gradually transformed into nanorods, and, finally, nanobelts with stable shapes as a result of surface energy minimization.

Phosphorylation of c-Jun N-terminal kinase in human hepatoblastoma cells is transiently increased by cold exposure and further enhanced by subsequent warm incubation of the cells.

During a cold preservation and reperfusion process of organs, cells are exposed to two major stresses, i.e. changes in oxygen concentration and temperature. c-Jun N-terminal kinase (JNK) /stress-activated protein kinase is activated by various stresses through its phosphorylation. Although hypoxia and subsequent reoxygenation is known to activate JNK, little is known about effects of hypothermia and subsequent rewarming on JNK activation. Thus, we investigated the activation of JNK in human hepatoblastoma (HepG2) cells exposed to a temperature of 5 degrees C and in those rewarmed at 37 degrees C. Western blot analysis using an anti-phospho-JNK antibody revealed that p54 JNK was transiently phosphorylated in cold-stressed cells. In addition, the phosphorylation of p54 JNK was further increased by rewarming of the cells. Since translational and transcriptional abilities were markedly reduced in the cold-stressed cells, effects of translation and transcription inhibitors on the phosphorylation of p54 JNK were determined. Cycloheximide, but not actinomycin D, increased the phosphorylation of p54 JNK in HepG2 cells. These results suggest that hypothermia alone transiently increases the p54 JNK phosphorylation possibly through reduction of protein synthesis and that rewarming after hypothermia stimulates the phosphorylation of p54 JNK.