Effects of Polymer–Wall Interactions on Entanglements and Dynamics of Confined Polymer Films
2017
Li, Sijia | Li, Jiawei | Ding, Mingming | Shi, Tongfei
Using Monte Carlo simulations combined with a geometric primitive path analysis method (Z1 algorithm), we investigate the effects of polymer–wall interactions on the entanglements and dynamics of the polymer films capped between two walls. We introduce a new parameter, the average number of near-neighboring particles of each monomer, to understand the effects of the polymer–wall interactions on the entanglements and dynamics of these confined systems. Our results show that the number of entanglements increases from the attractive polymer–wall interactions to the repulsive polymer–wall interactions. When the film thickness is greater than the bulk chain dimensions, the diffusion coefficient is a slowly decreasing function of the film thickness; however, when the film thickness is smaller than the bulk chain dimensions, the diffusion coefficient is an increasing function of the film thickness. However, for stronger polymer–wall interactions, although the number of entanglements decreases, the average number of the near-neighboring particles rapidly increases, which screens the effect of the disentanglements and thus limits the diffusivity of the polymers. Moreover, our simulations demonstrate that a critical attractive energy exists in the polymer–wall systems, where the diffusion coefficient reaches a maximum value and decreases toward stronger attractions or stronger repulsions. Our simulations provide new insights into the molecular mechanisms of the effects of polymer–wall interactions on the confined polymer films.
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