A Unifying Framework to Quantify the Effects of Boundary Stiffness, Polymer-Substrate Interactions and Substrate Roughness on the Dynamics of Thin Supported Polymer Films
Jack F. Douglas, Paul Hanakata, Francis W. Starr, Beatriz Betancourt
Changes in the dynamics of supported polymer films in comparison to bulk materials involve a complex convolution of effects, such as boundary thermodynamic interactions, boundary roughness and compliance, in addition to finite film thickness. We consider molecular dynamics simulations of substrate-supported, coarse-grained polymer films where these parameters are tuned separately to determine how each of these variables influence the molecular dynamics of thin polymer films. We find that all these variables significantly influence the film dynamics, leading to a seemingly intractable degree of complexity in the polymer film dynamics. However, by considering how these constraining variables influence string-like collective motion within the film, we show that all our observations can be understood in a unified and quantitative way. More specifically, the string model for glass-forming liquids implies that the changes in the structural relaxation of these films are governed by the changes to the average length of string-like cooperative rearrangement motions and this model is confirmed under all conditions by our simulations. Changing substrate interactions or thickness has a predictable effect on the activation free energy within this model, which makes this model promising for the rational design of film properties.
Journal of Chemical Physics
glass-formation, thin polymer films, string theory of dynamics, cooperative motion, fragility, decoupling
, , P.
, Starr, F.
and Betancourt, B.
A Unifying Framework to Quantify the Effects of Boundary Stiffness, Polymer-Substrate Interactions and Substrate Roughness on the Dynamics of Thin Supported Polymer Films, Journal of Chemical Physics
(Accessed June 7, 2023)