Cellulose nanomaterials (CNMs) combine low thermal conductivity, multiple interfaces, low density and high strength that are of interest in the design of phonon-engineered materials for thermal management. Anisotropic foams based on TEMPO-oxidized cellulose nanofibrils (TCNF) made by ice-templating exhibit very low radial –perpendicular to the columnar pores– thermal conductivity, paving the way to reduce the current energy consumption due to insufficient insulation.    <br/>The thermal conductivity of hygroscopic CNM-based foams and aerogels depends on the moisture uptake, the alignment of the fibrils or rod-like nanocrystals, the porosity and fibril-fibril separation distance. Here, we will show how anisotropic ice-templated foams and aerogels can be phonon-engineered by tuning the surface properties of cellulose nanofibrils (CNF) and nanocrystals (CNC). We will determine how the thermal conductivity of anisotropic CNM-based foams depends on the relative humidity (RH), the porosity, and fibril alignment in the pore walls and discuss how the surface chemistry of the fibrils is related to the moisture-induced swelling and the thermal conductivity and the phonon scattering of the foam walls. Preliminary results show that ice-templated foams made from CNC, instead of TCNF, displayed a reduced moisture uptake and a significantly improved toughness but the degree of alignment is influenced by the formation of liquid crystals above the critical concentration. Foams produced from hydrophobically modified fibrils, e.g. carboxymethylated cellulose nanofibrils (CM-CNF) having alkene or alkyne surface groups, exhibited a relatively low moisture uptake and a radial thermal conductivity that was much lower than the radial thermal conductivity of unmodified CM-CNF.

Tuning the thermal conductivity of phonon-engineered cellulose nanomaterial-based foams by modifying the surface chemistry

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.