Humidity-Dependent Thermal Boundary Conductance Controls Heat Transport of Super-Insulating Nanofibrillar Foams

Abstract

We show that anisotropic foams based on aligned cellulose nanofibrils are superinsulating also at high relative humidity (RH). Thermal conductivity measurements and non-equilibrium molecular dynamic simulations show that the moistureinduced swelling and increase of the inter-fibrillar distance results in a reduction of the thermal boundary conductance that exceeds the thermal conductivity increase due to water uptake up to 75% RH. Phonon engineering by moisture could be used to tailor the heat transfer properties of hygroscopic nanofibrillar materials.