Size-dependent elasticity of vinyl ester–TiO 2 nanocomposites: nonbonded molecular dynamics (Lennard–Jones and coulombic)

This paper investigates how filler size affects the elastic properties of a vinyl ester polymer nanocomposite reinforced with titanium dioxide (TiO2) nanoparticles using molecular dynamics (MD) simulations. The interaction between the nanoparticles and polymer chains is modeled as nonbonded, comprising Lennard–Jones and Coulombic terms. The elastic properties of the pure polymer and the nanocomposites are evaluated under uniaxial tension, uniaxial compression, and torsion. The results show that decreasing the filler size improves the mechanical response, increasing the tensile, compressive, and shear moduli. A simple three-phase estimate then predicts higher effective moduli for smaller particles, consistent with our MD-derived non-bonded energetics and the measured tensile, compressive, and shear responses. The “dense three-phase” model is quantitatively supported by analyzing the local density profiles and Radial Distribution Functions (RDF) of the vinyl ester monomers around the TiO2 nanoparticles. This provides the physical basis for the observed stiffening effect.