Hydrogen bonds dominated frictional stick-slip of cellulose nanocrystals.

Crystalline cellulose, the most abundant natural polymer on earth, features exceptional physical and mechanical properties. Using atomistic simulation, this study reports the mechanical behavior of cellulose-cellulose nanocrystal hydrophilic interface and systematically examines the impact of loading direction, interfacial moisture, misalignment and surface types. The density, orientation or distribution of interfacial hydrogen bonds are shown to explain the series of findings presented here, including stick-slip behavior, stiffness recovery after an irreversible slip, direction-dependent behavior and weakening induced by hydration or misalignment. Correlation analysis shows that, regardless of the various loading conditions, the interfacial stress, shear velocity and interaction energy are strongly correlated with the density of interfacial hydrogen bonds, which quantitatively supports the central role of hydrogen bonding. Based on this correlation, the friction force rendered by a single hydrogen bond is inferred to be fHB ∼1.3 E-10 N under a shearing speed of 1 m s-1.