Effect of Extent and Pattern of Methyl Substitution in Methylcellulose Chains on Multiscale Assembled Structure

Methylcellulose (MC) is a cellulose derivative with some hydroxyl groups replaced with methoxy groups. Because MC undergoes a thermoreversible gelation at elevated temperatures, it is widely used as a thickener in foods, construction materials, and hydrogels for biomedical applications. Commercial MC is typically synthesized using techniques that yield a heterogeneous substitution of methoxy groups along the polymer backbone, with a degree of substitution (DS) of around 1.8. Over the past decade, it has been shown that gelation of commercial MC chains occurs as the result of chains aggregating into semi-flexible fibrils that make up a gel. However, alternative synthesis methods can yield MC with a more homogenous substitution pattern and controlled block copolymers of MC monomers with different substitutions. Such changes to the distribution of hydrophobic groups along the MC backbone have been shown to have profound impact on the gelation temperature and behavior of MC, but the extent to which the structure of MC fibrils changes because of different substitution patterns remains unknown. A strong understanding of this relationship would allow design of MC with ideal properties for a given application, but has been limited by the large design space of methyl substitution pattern. In this work, we use coarse-grained molecular dynamics simulations to investigate the impact of substitution pattern on the self-assembly of MC chains in aqueous solution.