A coarse-grained model for nanocellulose with hydration interfaces revealing the anomalous mechanical enhancement

Abstract

Considering the humidity-sensitivity of nanocellulose, decoding the micromechanical mechanisms hidden in hydration interface is essential for tailoring the macroscopic properties. However, exiting mechanics frameworks based on molecular modeling remain challenging to predict the hydration interface-mediated mechanical behaviors of nanocellulose at the mesoscale, hindering the correlation from micro-interface to macro-mechanics. Herein, we developed a coarse-grained (CG) model integrating non-covalent interactions and fiber-level hierarchical stacking, which unveils the anomalous mechanical enhancement of nanocellulose with hydration interfaces. The CG model, validated by all-atom (AA) simulations, accurately captured the modulus and strength scale law with overlap length, until the fiber fracture-dominated saturated state. Our results revealed how hydration extent effects the interfacial mechanics, showing that moderate hydration can enhance both toughness and strength by plasticizing hydrogen-bonding networks, while excessive hydration weakening the shear strength. Beyond the limit that AA simulations can predict, an optimal overlap regime (∼120–180 nm) was identified, where hydration-mediated interfaces can enhance the strength and toughness simultaneously. This study established a cross-scale theoretical modeling framework bridging the microscale hydration interface and macroscale mechanical regulation of nanocellulose materials, which can provide the bottom-up rational guidance for designing strong and tough nanocomposites with weak non-covalent interfaces.