Ultra-high Thermal Conductivity of Spider Silk: Protein Function Study with Controlled Structure Change and Comparison
Technical Report,01 Jul 2012,30 Jun 2015
Iowa State University of Science and Technology Ames United States
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In the past three years, we have conducted extensive research to study the structure of spider silks and investigate how the structure affects the silks thermal transport. The comparison of thermal conductivity k and structural information between the naturally spun and manually spun spider silks demonstrates that the alignment of the antiparallel beta-sheet crystals in spider silks plays one of the most important roles in improving thermal transport. Various structural manipulations have been introduced by casting the silk protein into different shapes, varying the speed of manual silk spinning, using different silks from the same spider and silks from different types of spiders. The thin width of silks has been proved to significantly improve k. The silks from the spiders in unhealthy conditions also showed a higher k. Rough structures would enhance phonon scattering and thus lower k. A small range of the variation of the spinning rate in producing spider silks would not obviously increase k, when no significant shape change is induced. The organic solvent in silver paste involved in our experiment has little effect in decreasing k. On the other hand, to go deeper into the nanoscale nature of the structure of spider silks, X-ray diffraction XRD has been employed to study the crystallite size of spider silks. Also a lab-developed thermal reffusivity theory has been employed to study thermal properties of spider silks at low temperatures down to 10 K. The crystallite size obtained through XRD and mean free path of the defect-induced phonon scattering are nicely consistent with each other.