The effects of filler-matrix interface strength, filler shape and filler dispersion on the mechanical properties of polymer nanocomposites

Over the last few decades, scientific and industrial interests on nanoparticle reinforced polymer composite (NRPC) materials have grown extensively primarily because of their immense potential to improve the mechanical, electrical, optical, barrier, fire retardant and many other properties while keeping the cost of production lower. In practice, nanoparticles come in several shapes and sizes with varying level of aggregated forms. However, a controlled and repeatable production of NRPC's from these particles is still far away from reality. In other words, it is still not known how different process level parameters such as nanoparticle size, shape, dispersion, filler-matrix interface, filler functionality, filler electrostatic states etc. control the mechanical and other properties. In this work, we have considered three important process level variables, namely, filler-matrix interface strength, filler shape and filler dispersion to understand their role on the mechanical properties of nanocomposites using molecular dynamics simulation. Two different shapes of nanoparticles have been considered, spherical fullerene buckyballs and cubic nanodiamond nanoprticles. The matrix system is modeled with linear low density polyethylene polymer. Degree of nanoparticle dispersion is studied by developing molecular models of nanocomposites by placing twenty seven nanoparticles in the PE matrix either in uniformly dispersed or in agglomerated form. The interface interaction between polymer and filler has been modeled by Van dar Walls (VDW) interaction and the intensity of interface strength has been varied by adjusting the VDW attractive potential parameter. The stress-strain responses for all models have been obtained by subjecting each model with incremental hydrostatic strain fields and by recording the corresponding virial stress fields. It has been observed, the degree of dispersion has the most critical role on the mechanical properties of NRPCs, and we conclude that the better the dispersion the better the mechanical properties of NRPCs. The shape of nanoparticles and polymer-nanoparticle interface have relatively less significant role. Details will be discussed in the paper.