An energy-based approach to study the aggregation/agglomeration phenomenon in polymer nanocomposites: Dispersion force against inter-particle cohesion

In this study, a novel method was proposed to predict the size and content of the nanoparticle aggregates/agglomerates in polymer nanocomposites based on the characteristics of the mixer, cohesion energy between nanoparticles and their content in the system. The internal energy equilibrium was evaluated by calculating the induced mixing energy by the mixer, aggregation, and agglomeration energies. An analytical model was designed to predict the tensile modulus of the system based on dispersion content and size of the aggregates/agglomerates. In addition, the tensile modulus of the aggregates/agglomerates was defined by developing Wacke's empirical equation. Two sets of PP and PA6 nanocomposite samples, containing 1-3 vol% of silica nanoparticles, were prepared and tested to verify the theoretical results. The applied nanoparticles were subjected to surface modification processes to maximize their compatibility with their surrounding polymer matrix. Different tests, including FE-SEM, contact-angle and tensile, were used to determine the mechanical/physical characteristics of the samples. The predicted results for the size of the aggregated/agglomerated domains were very close to those defined using FE-SEM tests. On the other hand, the predicted tensile moduli based on the content, size and mechanical characteristics of the aggregated/agglomerated domains were acceptably accurate considering the tensile test results.