Molecular Dynamics Investigation of Additive Rigidity Effects on Mechanical Properties and Relaxation Dynamics of Thermosetting Polymeric Coatings

This work uses coarse-grained molecular dynamics simulations to determine how the bending rigidity of nanofiller additives regulates the relaxation and mechanical behavior of cross-linked thermosetting coating materials. Understanding this molecular control is important for designing protective organic coatings whose stiffness, durability, and service stability can be tailored. Increasing additive rigidity causes the additive chains to adopt more extended conformations, as reflected by a larger radius of gyration R g, whereas the network conformation of the thermoset matrix and the overall mixture conformation change only modestly. Analysis of the structural relaxation time τ α shows that the glass-transition temperature T g, Vogel temperature T 0, and kinetic fragility all increase as the additives become less flexible. In contrast, when temperature is normalized by T g, both τ α and the mechanical moduli, including shear modulus G and tensile modulus E, fall onto common master curves for mixtures with different additive stiffness. The same normalization does not collapse the Debye–Waller factor, ⟨ u 2 ⟩. Nevertheless, ⟨ u 2 ⟩ remains closely linked to the moduli and therefore provides a molecular measure of local stiffness fluctuations. Systems containing stiffer additives show higher local stiffness and stronger elastic heterogeneity. These results clarify the molecular role of additive rigidity in thermoset/additive coatings and provide guidance for developing high-performance coating systems with improved mechanical robustness and protective capability. The conclusions are specific to physically blended, chemically neutral, additive-rich coarse-grained systems and are not intended to imply loading- or interface-independent universality.