Reversible transition between isotropic and anisotropic thermal transport in elastic polyurethane foams

Titelangaben

Chau, Mokit ; Kopera, Bernd A. F. ; Machado, Vanessa R. ; Tehrani, Sepehr Mastour ; Winnik, Mitchell A. ; Kumacheva, Eugenia ; Retsch, Markus:
Reversible transition between isotropic and anisotropic thermal transport in elastic polyurethane foams.
In: Materials Horizons. Bd. 4 (2017) Heft 2 . - S. 236-241.
ISSN 2051-6355
DOI: https://doi.org/10.1039/C6MH00495D

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Abstract

The dynamic and orientational control over the flow of heat is becoming increasingly important in current insulation applications. In this contribution we introduce an elegant way to fabricate highly anisotropic polyurethane foams via freeze casting from an aqueous dispersion. Such elastic foams demonstrate not only orientation dependent Young’s moduli, but also a good recoverability after compression. Most importantly, they are distinctly more insulating across their perpendicular than their parallel orientation. This anisotropy, however, can be turned on and off by appropriate choice of the gas phase. The thermal anisotropy is lost and an isotropic thermal transport is observed, when using Helium as gas phase. The degree of anisotropy can be adjusted via the gas pressure or the gas composition. We demonstrate that one can dynamically and reproducibly transition between such modes of isotropic and anisotropic thermal transport.