Molecular levers enable anomalously enhanced strength and toughness of cellulose nanocrystal at cryogenic temperature

The quest for widespread applications especially in extreme environments accentuates the necessity to design materials with robust mechanical and thermodynamic stabilities.Almost all existing materials yield temperature-variant mechanical properties,essentially determined by their different atomic bonding regimes.In general,weak non-covalent interactions are considered to diminish the structural anti-destabilization of covalent crystals despite the toughening effect.Whereas,starting from multiscale theoretical modeling,we herein reveal an anomalous stabilizing effect in cellulose nanocrystals(CNCs)by the cooperation between the non-covalent hydrogen bonds and covalent glucosidic skeleton,namely molecular levers(MLs).It is surprising to find that the hydrogen bonds in MLs behave like covalent bindings under cryogenic conditions,which provide anomalously enhanced strength and toughness for CNCs.Thermodynamic analyses demonstrate that the unique dynamical mechanical behaviors from ambient to deep cryogenic temperatures are synergetic results of the intrinsic temperature dependence veiled in MLs and the overall thermo-induced CNC destabilization/amorphization.As the consequence,the variation trend of mechanical strength exhibits a bilinear temperature dependence with~77 K as the turning point.Our underlying investigations not only establish the bottom–up interrelations from the hydrogen bonding thermodynamics to the crystal-scale mechanical properties,but also facilitate the potential application of cellulose-based materials at extremely low temperatures such as those in outer space.