Thermophysical properties study of micro/nano materials

Thermal transport in micro/nano materials is very critical, not only because the thermal property may have important influence on the performance of the materials, but also because the change of this property can reflect the inner structure change. Due to the complicated structure and small scale, the thermal properties of biomaterials, such as silkworm silk, spider silk and human head hair, are still not fully understood. Experiments are conducted on silkworm silk, spider silk and human head hair to explore their thermal properties and potential applications. This work reports on the first time study of thermal transport in the axial direction of single silkworm silks. The measured thermal diffusivity of relaxed silkworm silk and thermal conductivity are 0.39 × 10 -6 ~2.03 × 10 -6 m 2 s -1 and 0.54~6.53 W m -1 K -1 , respectively. The thermal diffusivity of silkworm silk increases up to 263% upon elongation up to 63.8%. For one of the samples studied (sample 5), its thermal conductivity goes up to 13.1 W m -1 K -1 after elongation of 68.3%, surpassing many other polymers. Three factors combine together to give rise of the remarkable thermal diffusivity increase: alignment improvement of sheets blocks, straightening of -helices and random coils under stretching, and structural transformation from -helices and random coils to β-sheets crystal by elongation (confirmed by our Raman spectroscopy study). Thermal path break-down is observed when elongation is beyond 63.8%. Our Raman spectroscopy study confirms