Regulation of the dynamics of polymer films by modifying the stiffness and length of polymer brushes

Regulating the dynamic behavior of polymer films is of great significance for their practical applications. Polymer brushes have emerged as a powerful strategy for modulating the dynamics of polymer films. However, how the influence on the dynamics varies with the molecular weight of the polymer brush remains unclear, with contradictory results reported in the literature. In this study, coarse-grained molecular dynamics simulations are employed to investigate the influence of end-grafted polymer brushes on the dynamics of an overlying film of fully flexible matrix polymers. The effects of the stiffness and length of the end-grafted polymers are systematically examined. For fully flexible brushes, the influence on the dynamics of matrix polymers is relatively weak, as the brush forms a dense layer that effectively suppresses interpenetration with the matrix polymers. Moreover, this modulatory effect weakens with increasing polymer length of the brush. In contrast, semi-flexible brushes exhibit the opposite trend: longer end-grafted polymers strengthen interactions between the brush and matrix polymers, promoting greater interpenetration and stronger modulation of film dynamics. However, further increase in chain stiffness causes aggregation of the brush, thus weakening its influence on the dynamics of matrix polymers. This work highlights the critical role of chain stiffness in designing polymer brushes for regulating the dynamic behavior of thin polymer films.