(169dj) Development of a Modifiable Atomistic Cellulose Nanocrystal Model

The remarkable properties of cellulose nanocrystals (CNCs), a widely used natural polymeric nanomaterial in various sustainable industries, result from the unique structural characteristics of CNCs. In particular, the trans-gauche (tg) conformation of primary alcohol groups on the cellulose molecules allows for the formation of an extensive network of intra-chain and inter-chain hydrogen bonds. The high population of hydrogen bonds within the interior domain of cellulose nanocrystals confers high stiffness and mechanical integrity, enabling their use as reinforcement material in numerous applications. However, most atomistic-scale computational studies of CNCs have failed to accurately reproduce the high population of tg conformations within the crystalline domain of CNCs, leading to deviations in the calculated crystalline properties from experimental observations.

The conformation of primary alcohol groups and hydrogen bond formation stem from a complex interplay of interactions between different particles, such as angle vibrations, torsional forces, electrostatic, and van der Waals interactions. Therefore, accurate modeling of CNCs demands the use of an appropriate force field and charge model. In the study presented herein, we used a combination of the OPLS-AA force field and CM5 charge model, denoted as the OPLS-CM5 model, and observed significant improvement in the atomistic-scale models of CNCs. The OPLS-CM5 model yielded a 90% occupancy of tg conformations and hydrogen bonds, enhancing the previous OPLS-AA model by nearly 50%.

Given the excellent capability of this model in maintaining the crystalline properties of CNCs, it could be extended to the simulation of surface-functionalized CNCs without affecting their crystalline properties—an issue that has hindered previous models. Understanding the dynamics of surface-functionalized CNCs enables tailoring their surface chemistry for specific applications.