Particles size and aspect ratio effects on the dielectric enhancement in polymer composites

In aerospace applications, light weight is a critical criterion; the lighter the better. For that reason, polymer nanocomposites promise to replace conventional composites since they require lower volume content to achieve comparable or higher enhancement. In this work, the effect of the size of the particles and their aspect ratio on polymer nanocomposites properties is studied. TiO2 particles with sizes ranging from 10nm to 2microns and aspect ratios from 1 to 15 are added to PVDF matrix. Composites dispersion was compared when a coupling agent versus dispersant was added. Dielectric properties are measured using Novocontrol system in a wide range of frequencies. It is believed that the interphase between the particles and the polymer plays an important role in enhancing the dielectric behavior due to possible interfacial dipole formation. Interaction between the particles and the matrix is quantified with Dynamic Mechanical Analysis (DMA). Particles dispersion is qualified using Scanning Electron Microscopy (SEM). Composites morphology is further characterized with Differential Scanning Calorimetry (DSC). Characterization results show that there is a correlation between particle size and aspect ratio in defining the enhancement in polymer composites properties. The smallest particles with the highest aspect ratio contributed the highest improvement. This can be explained by the huge surface to volume ratio these particles have and their polarization anisotropy.