Understanding the Role of Cohesive Interaction in Mechanical Behavior of a Glassy Polymer

A Alesadi and WJ Xia, MACROMOLECULES, 53, 2754-2763 (2020).

DOI: 10.1021/acs.macromol.0c00067

Understanding the mechanical behavior of glassy polymers at a fundamental molecular level is of critical importance in engineering and technological applications. Among various molecular parameters, cohesive interactions between polymer chains are found to play a key role in influencing the thermomechanical response of glass-forming polymers. Here, we employ atomistically informed coarse-grained molecular dynamics 0 0.E (CG-MD) simulations to study the mechanical properties of the polymer material in a glassy state. Built upon the recently developed "energy renormalization" (ER) coarse-graining approach, we take polycarbonate (PC) as a model system to systematically explore the shear response and dynamical heterogeneity of polymers under the influence of cohesive interactions. Our results show that the polymer with a larger cohesive interaction exhibits a greater shear modulus and a higher degree of dynamical heterogeneity, which is uncovered by evaluating the local molecular stiffness. This pronounced dynamical heterogeneity with increasing cohesive interactions is found to be closely correlated to the packing frustration at a molecular level, which can be quantified by the glass "fragility", a measure of the relative strength of the temperature dependence of relaxation. Our findings highlight the critical role of cohesive interaction on the mechanical behavior of glassy polymers and provoke the idea of achieving a tailored design of polymer materials via molecular-level engineering.

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