Atomic investigation on optimal interfacial bonding for enhanced fracture properties in polymer nanocomposites

Functionalization of nanofillers is known to have stiffening and strengthening effects on nanocomposites through improved interfacial bonding. However, the optimality in the interfacial bonding is generally not reported in the literature. This issue is addressed here through a series of reactive molecular dynamics simulations on carbon nanotube reinforced polymer nanocomposite. For various degrees of functionalization, uniaxial tension conditions are simulated to study the stress-strain behavior, crack propagation, and fracture toughness. The J-integral is used to quantify the fracture toughness. Through these simulations we demonstrate the existence of an optimal degree of functionalization for maximum enhancement in elastic property, tensile strength, ductility, and fracture toughness. The underlying mechanics behind this optimality is identified through careful studies on crack propagation mechanisms, including crack arresting and formation of new crack surfaces. This optimality, which might also be expected in other material systems, will help in designing efficient nanocomposites.