Investigating the internal structure of methylcellulose fibrillar assembly in aqueous solutions using multiscale modeling and simulations

Methylcellulose (MC) is a cellulose derivative where some or all hydroxyl groups are replaced by methoxy groups. Aqueous solutions of MC demonstrate a unique phase behavior where MC chains are soluble in water at lower temperatures but assemble into semi-flexible fibrils and fibrillar networks at elevated temperatures. Structural analysis via small-angle scattering (Macromolecules, 2018, 51, pp7767) further reveals consistent MC fibril diameters at varying molecular weights and concentrations. How the MC chains assemble into consistent fibril diameter has been debated by various groups and yet no conclusive answer has been found. To answer this question, we combine coarse-grained (CG) and atomistic molecular dynamics (MD) simulations. CG MD simulations show how MC chains assemble into fibrils with consistent diameters; chains align parallel to each other during assembly into fibrils with a select few outermost MC chains twisting around the fibril. Atomistic MD simulations of MC chains in explicit water show increased twisting of MC chains in the fibrils at elevated temperatures as compared to room temperature suggesting that the increased hydrophobicity and bulkiness of the methoxy groups as compared to hydroxyl groups is the driving force for such twisted MC chain configurations.