Unified Model of Lattice Thermal Conductivity in Crystalline Cellulose Iβ

Cellulose is one of the most abundant natural polymers and is a sustainable energy source. Under delignification and densification, cellulose was found to be having outstanding radiative cooling properties. Thus, phonons, being the dominant heat carrier in crystalline cellulose, are of great importance in understanding the energy transfer mechanism. In this work, we investigate the thermal transport in crystalline Cellulose Iβ using molecular dynamics, lattice dynamics with ReaxFF that has been modified for the study of phonons. Different thermal transport models including Green-Kubo (GK) formula, Allen-Feldman, Cahill-Watson-Pohl, the ideal phonon gas models, and the contribution from the off-diagonal terms in the heat-flux operator are applied to calculate the thermal conductivity in cellulose. Our results indicate that the unified model including both diagonal and off-diagonal contribution of heat-flux operator shows the best agreement with GK and experiments among all the theoretical models. Compared with the phonon gas model, the leading contribution of the coherences' terms to thermal conductivity indicates its predominant role in thermal transport in cellulose. Our study provides insights into the understanding of thermal transport mechanisms in complex molecular crystals.