In comparison with the advancement of switchable, nonlinear, and active components in electronics, solid-state thermal components for actively controlling heat flow have been extremely rare. We demonstrate a high-contrast and reversible polymer thermal regulator based on the structural phase transition in crystalline polyethylene nanofibers. This structural phase transition represents a dramatic change in morphology from a highly ordered all-trans conformation to a combined trans and gauche conformation with rotational disorder, leading to an abrupt change in phonon transport along the molecular chains. For five nanofiber samples measured here, we observe an average thermal switching ratio of ~8× and maximum switching ratio of ~10×, which occurs in a narrow temperature range of 10 K across the structural phase transition. To the best of our knowledge, the ~10× switching ratio exceeds any reported experimental values for solid-solid and solid-liquid phase transitions of materials. There is no thermal hysteresis observed upon heating/cooling cycles.
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Observation of solid-state bidirectional thermal conductivity switching in antiferroelectric lead zirconate (PbZrO3)
Abstract Materials with tunable thermal properties enable on-demand control of temperature and heat flow, which is an integral component in the development of solid-state refrigeration, energy scavenging, and thermal circuits. Although gap-based and liquid-based thermal switches that work on the basis of mechanical movements have been an effective approach to control the flow of heat in the devices, their complex mechanisms impose considerable costs in latency, expense, and power consumption. As a consequence, materials that have multiple solid-state phases with distinct thermal properties are appealing for thermal management due to their simplicity, fast switching, and compactness. Thus, an ideal thermal switch should operate near or above room temperature, have a simple trigger mechanism, and offer a quick and large on/off switching ratio. In this study, we experimentally demonstrate that manipulating phonon scattering rates can switch the thermal conductivity of antiferroelectric PbZrO 3 bidirectionally by −10% and +25% upon applying electrical and thermal excitation, respectively. Our approach takes advantage of two separate phase transformations in PbZrO 3 that alter the phonon scattering rate in different manners. In this study, we demonstrate that PbZrO 3 can serve as a fast (<1 second), repeatable, simple trigger, and reliable thermal switch with a net switching ratio of nearly 38% from ~1.20 to ~1.65 W m −1 K −1 .
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- PAR ID:
- 10331647
- Date Published:
- Journal Name:
- Nature Communications
- Volume:
- 13
- Issue:
- 1
- ISSN:
- 2041-1723
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Classical materials readily switch phases (solid to fluid or fluid to gas) upon changes in pressure or heat; however, subsequent reversion of the stimulus returns the material to their original phase. Covalently cross-linked polymer networks, which are solids that do not flow when strained, do not change phase even upon changes in temperature and pressure. However, upon the addition of dynamic cross-links, they become stimuli responsive, capable of switching phase from solid to fluid, but quickly returning to the solid state once the stimulus is removed. Reported here is the first material capable of a bistable switching of phase. A permanent solid to fluid transition or vice versa is demonstrated at room temperature, with inherent, spatiotemporal control over this switch in either direction triggered by exposure to light.
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Controlling heat flow is a key challenge for applications ranging from thermal management in electronics to energy systems, industrial processing, and thermal therapy. However, progress has generally been limited by slow response times and low tunability in thermal conductance. In this work, we demonstrate an electronically gated solid-state thermal switch using self-assembled molecular junctions to achieve excellent performance at room temperature. In this three-terminal device, heat flow is continuously and reversibly modulated by an electric field through carefully controlled chemical bonding and charge distributions within the molecular interface. The devices have ultrahigh switching speeds above 1 megahertz, have on/off ratios in thermal conductance greater than 1300%, and can be switched more than 1 million times. We anticipate that these advances will generate opportunities in molecular engineering for thermal management systems and thermal circuit design.
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This article shows experimentally that an external electric field affects the velocity of the longitudinal acoustic phonons (
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Abstract New technologies are emerging which allow us to manipulate and assemble 2-dimensional (2D) building blocks, such as graphene, into synthetic van der Waals (vdW) solids. Assembly of such vdW solids has enabled novel electronic devices and could lead to control over anisotropic thermal properties through tuning of inter-layer coupling and phonon scattering. Here we report the systematic control of heat flow in graphene-based vdW solids assembled in a layer-by-layer (LBL) fashion. In-plane thermal measurements (between 100 K and 400 K) reveal substrate and grain boundary scattering limit thermal transport in vdW solids composed of one to four transferred layers of graphene grown by chemical vapor deposition (CVD). Such films have room temperature in-plane thermal conductivity of ~400 Wm−1 K−1. Cross-plane thermal conductance approaches 15 MWm−2 K−1for graphene-based vdW solids composed of seven layers of graphene films grown by CVD, likely limited by rotational mismatch between layers and trapped particulates remnant from graphene transfer processes. Our results provide fundamental insight into the in-plane and cross-plane heat carrying properties of substrate-supported synthetic vdW solids, with important implications for emerging devices made from artificially stacked 2D materials.
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1038/s41467-022-29023-y
