Controlling thermomechanical anisotropy is important for emerging heat management applications such as thermal interface and electronic packaging materials. Whereas many studies report on thermal transport in anisotropic nanocomposite materials, a fundamental understanding of the interplay between mechanical and thermal properties is missing, due to the lack of measurements of direction‐dependent mechanical properties. In this work, exceptionally coherent and transparent hybrid Bragg stacks made of strictly alternating mica‐type nanosheets (synthetic hectorite) and polymer layers (polyvinylpyrrolidone) were fabricated at large scale. Distinct from ordinary nanocomposites, these stacks display long‐range periodicity, which is tunable down to angstrom precision. A large thermal transport anisotropy (up to 38) is consequently observed, with the high in‐plane thermal conductivity (up to 5.7 W m−1 K−1) exhibiting an effective medium behavior. The unique hybrid material combined with advanced characterization techniques allows correlating the full elastic tensors to the direction‐dependent thermal conductivities. We, therefore, provide a first analysis on how the direction‐dependent Young's and shear moduli influence the flow of heat.

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The low thermal conductivity of amorphous polymers typically prevents their usage in thermal management applications. Therefore, increasing their intrinsic thermal conductivity poses an exciting scientific challenge. One approach is to promote attractive interchain interactions. Here, we investigate the thermal conductivity of several ampholytic polymers. This unique class of polymers offers H-bond donor and acceptor groups in each repeat unit and constitutes an onecomponent system. We use IR spectroscopy to characterize the bonding strength and motifs based on the carbonyl peak. For the dry ampholytic polymers, we find a correlation between H-bond strength and thermal conductivity. We also characterized the influence of hydration at various relative humidity conditions, which mostly led to an increase in thermal conductivity. This increase can be rationalized by the formation of a water-polymer nanocomposite material and can be described by volume-weighted mixing models. conductivity. This is an ongoing challenge to be addressed by polymer chemists and engineers over the next years. ASSOCIATED CONTENT Supporting Informationthermal conductivity measurements, IR spectroscopy of individual polymers, DSC measurements, effective medium mixing models, and microscopy of the transducer layer