RESUMEN
A highly efficient thermal rectification applicable to large panels still needs to be developed. Here, we experimentally achieve a high thermal rectification efficiency of 33% by carefully engineering elastic modulus asymmetry in a centimeter-scale bilayered silver-graphene oxide sponge. The thermal conduction primarily occurs in the out-of-plane direction, and the forward heat flow direction is from the hard silver to the soft graphene oxide. Surprisingly, the forward heat flow direction is reversed when a silver layer is formed on a harder polystyrene foam. The forward direction is always from the harder side to the softer side, and the asymmetry in elastic modulus is suggested as a possible mechanism based on the one-dimensional Frenkel-Kontorova (FK) model. The finite element analysis indicates that other mechanisms such as temperature-dependent thermal conductivity and radiation asymmetry cannot explain the high rectification efficiency. This scalable work over a wide temperature range may find immediate industrial applications.
RESUMEN
The dependence of the electrical resistance on materials' geometry determines the performance of conductive nanocomposites. Here, we report the invariable resistance of a conductive nanocomposite over 30% strain. This is enabled by the in situ-generated hierarchically structured silver nanosatellite particles, realizing a short interparticle distance (4.37 nm) in a stretchable silicone rubber matrix. Furthermore, the barrier height is tuned to be negligible by matching the electron affinity of silicone rubber to the work function of silver. The stretching results in the electron flow without additional scattering in the silicone rubber matrix. The transport is changed to quantum tunneling if the barrier height is gradually increased by using different matrix polymers with smaller electron affinities, such as ethyl vinyl acetates and thermoplastic polyurethane. The tunneling current decreases with increasing strain, which is accurately described by the Simmons approximation theory. The tunable transport in nanocomposites provides an advancement in the design of stretchable conductors.