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To push upper boundaries of thermal conductivity in polymer composites, understanding of thermal transport mechanisms is crucial. Despite extensive simulations, systematic experimental investigation on thermal transport in polymer composites is limited. To better understand thermal transport processes, we design polymer composites with perfect fillers (graphite) and defective fillers (graphite oxide), using polyvinyl alcohol (PVA) as a matrix model. Measured thermal conductivities of ~1.38 ± 0.22 W m−1K−1in PVA/defective filler composites is higher than those of ~0.86 ± 0.21 W m−1K−1in PVA/perfect filler composites, while measured thermal conductivities in defective fillers are lower than those of perfect fillers. We identify how thermal transport occurs across heterogeneous interfaces. Thermal transport measurements, neutron scattering, quantum mechanical modeling, and molecular dynamics simulations reveal that vibrational coupling between PVA and defective fillers at PVA/filler interfaces enhances thermal conductivity, suggesting that defects in polymer composites improve thermal transport by promoting this vibrational coupling.
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Ligand Crosslinking Boosts Thermal Transport in Colloidal Nanocrystal Solids
Abstract The ongoing interest in colloidal nanocrystal solids for electronic and photonic devices necessitates that their thermal‐transport properties be well understood because heat dissipation frequently limits performance in these devices. Unfortunately, colloidal nanocrystal solids generally possess very low thermal conductivities. This very low thermal conductivity primarily results from the weak van der Waals interaction between the ligands of adjacent nanocrystals. We overcome this thermal‐transport bottleneck by crosslinking the ligands to exchange a weak van der Waals interaction with a strong covalent bond. We obtain thermal conductivities of up to 1.7 Wm−1 K−1that exceed prior reported values by a factor of 4. This improvement is significant because the entire range of prior reported values themselves only span a factor of 4 (i.e., 0.1–0.4 Wm−1 K−1). We complement our thermal‐conductivity measurements with mechanical nanoindentation measurements that demonstrate ligand crosslinking increases Young's modulus and sound velocity. This increase in sound velocity is a key bridge between mechanical and thermal properties because sound velocity and thermal conductivity are linearly proportional according to kinetic theory. Control experiments with non‐crosslinkable ligands, as well as transport modeling, further confirm that ligand crosslinking boosts thermal transport.
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- Award ID(s):
- 1654337
- PAR ID:
- 10142875
- Publisher / Repository:
- Wiley Blackwell (John Wiley & Sons)
- Date Published:
- Journal Name:
- Angewandte Chemie International Edition
- Volume:
- 59
- Issue:
- 24
- ISSN:
- 1433-7851
- Page Range / eLocation ID:
- p. 9556-9563
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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