Dependence of Crystallization on Bond Lengths in Polymer Thin Films

Abstract

Polymer thin films are commonly used in applications ranging from drug delivery towastewater treatment. Glassy polymers are of particular interest because the natureof glasses and the glass transition are still not well understood. Crystallization-resistantpolymer models are needed in order to simulate polymer glasses in non-bulksystems such as nanofilms, in which heterogeneous nucleation induced by confiningsurfaces is a strong possibility. The finitely extensible nonlinear elastic (FENE) bead-springpolymer model has long been used in simulations because of its computationalefficiency, but Mackura et al. (J. Polym. Sci. B. 2014, 52, 134-40) showed that thestandard FENE model crystallizes in the presence of a well-ordered wall, suggestinginstead a modified FENE model with shorter bond lengths and increased nucleationresistance. In this work, MD simulations are used to examine three FENE models withvarying bond lengths. The systems are cooled past the glass transition temperatureand equilibrated. Density profiles and bond angle analyses are employed for the bulkpolymer, while heat maps, pair correlation functions, and static structure factors arecalculated for each layer. Structural data is used to quantify the extent of orderingand examine the types of crystal structures induced in each polymer model.