Hypothesis: The dispersion state of nanoparticles cannot be evaluated accurately by rheological and mechanical testes because their agglomerates break down under applied stress leading to changes in their microstructure. Additionally, the contribution of interparticle interactions to macroscopic properties such as rheological and mechanical properties is still unclear. This is mainly due to the combined effects of interparticle interactions and the particle-polymer interactions. Microscopic measurements which can only provide information on a very small section of a sample are not reliable for this purpose. However, electrical tests as nondestructive methods can be used to assess the microstructure and cluster formation in nanocomposite structures. In addition, it is possible to detect separately the effect of filler-filler interactions using dielectric properties and with a proper choice of materials.
Methods: In this study, ZnO/polystyrene (PS) nanocomposites were prepared through conventional mixing, dispersive mixing and surface particle treatment to control the particle dispersion states. The dispersion state of nanoparticles has been analyzed using their optical, electrical and rheological properties.
Findings: The results showed that storage modulus increased with increasing filler dispersion, which could be attributed to the increase in interfacial layer and the higher modulus of nanocomposite relative to that of the bulk polymer matrix. The SEM images showed that the dispersive mixing and surface treatment of ZnO nanoparticles with oleic acid improved the dispersion of ZnO particles inside the PS matrix. On the other hand, increase in dispersion decreases the electrical conductivity and dielectric constant due to greater interparticle distance and reduction of dipole-dipole interactions, respectively. Hence, it is possible to detect the particle dispersion state by rheological and electrical properties.