(735d) Surface Interaction between Short-Chain Cellulosic Polymers and Cellulose Nanocrystals from Molecular Simulation

Cellulose nanocrystal (CNC) is a material with a spectrum of properties, and it has found application in a variety of novel products, alone and in combination with other materials due to its interactive properties. Notably, interactions between CNC with certain cellulosic polymers give rise to intriguing new properties not found in pure CNC. CNC-polymer hybrid systems have seen applications in special materials like Pickering emulsions, foams and gels etc. However, the nature of such interactions remain unknown. We used all-atom molecular simulation for probing the interaction between short-chain cellulosic polymers with specific surfaces of CNC. Effects of salt addition and surface sulphation -- common conditions of CNC applications -- are also investigated. We used the free energy difference values obtained in terms of the PMF (potential of mean force) as the tool to understand the relative interactions between the oligomers and CNC. From our observation in terms of PMF and other qualitative and quantitative results, we propose that there are two driving forces which switch and take effect at specific distances as we move away or towards the surface. We made observations in terms of hydrogen bonding interactions within the oligomer chain and with water, which strongly supports and correlates well with our theory and observations. Physically, we conclude that all physical components (CNC surface, oligomer type and bulk properties) have implication on the CNC-polymer interactions. Closer to the surface the molecular interactions such as hydrogen bonds control the extent of interactions (adsorption and desorption) and farther from the surface the bulk interactions between polymer and solvent (water) control the interactions. Overall, we arrive at a conclusion that the balance between polymer's ability to form hydrogen bonds with the surface and their interactions with the bulk solvent control the adsorption and desorption phenomena. Further investigation will focus on coarse-grained modeling of the system for the interaction of longer polymer chains with CNC.