Origins of the Suppression of Fibril Formation in Grafted Methylcellulose Solutions

We utilize coarse-grained molecular-dynamics simulations to probe the influence of grafting on the conformation and aggregation of methylcellulose chains in water, inspired by the recent experiments on solutions of methylcellulose (MC) chains grafted with polyethylene glycol (PEG) that showed inhibition of methylcellulose fibril formation at high PEG-grafting densities [S. Morozova et al., Macromolecules (Washington, DC, U. S.) 51, 9413 (2018)]. These simulations reveal three features of the grafted system that should frustrate fibril assembly. First, multichain simulations indicate that the distance between the centers of mass of the chains increases at high grafting densities, suggesting that the ability to form collapsed structures is disrupted. Second, single-chain simulations using grafted MC show that the formation of the precursor toroidal structure responsible for fibril formation is hampered at high grafting densities. Third, the frequency spectrum of conformational fluctuations indicates that low-frequency modes dominate at higher grafting densities, suggesting a larger decorrelation time in conformational fluctuations. Together, these results provide a macromolecular basis for the suppression in fibril formation in grafted methylcellulose solutions for grafting densities exceeding approximately 10%.