Investigation of the interface in nanodielectrics using electrostatic force microscopy

The improved electrical properties of nanodielectrics compared to micro-filled and unfilled polymers are credited largely to the interfacial region surrounding the nanoparticles embedded in the polymer matrix. However, the interface is yet to be investigated extensively. In the present work, an experimental method using electrostatic force microscopy (EFM) has been proposed to probe the interface in nanocomposites. The EFM in the direct current (DC) mode maps the gradient of the electrostatic force to a phase shift in the oscillation of the AFM cantilever. Barium titanate (BaTiO ₃ ) nanoparticles are used as fillers in epoxy resin in this work. A 3-D electrostatic model based on the finite element method (FEM) is developed to compute the expected phase shift based on the material properties of the polymer and its nanofillers. A match between experimental and computational EFM data yields an estimate for the dielectric constant and thickness of the proposed interface around each particle. Further, particle size distribution of the nanoparticles obtained using characterization techniques like transmission electron microscopy (TEM) and atomic force microscopy (AFM) are found to support the estimates obtained through the EFM model.