Designing a new electrical insulating nanocomposite with chosen nanoparticles and matrix while targeting specific dielectric properties is still the Holy Grail in the domain of electrical engineering. The main challenge remains to understand the physical processes at the interphase between the nanoparticle and the matrix, at the nanoscale, and the impact of this interphase on the nanocomposite behavior at the macroscale. An interphase properties investigation has been developed, combining wellcontrolled low density polyethylene (LDPE)/ boron nitride (BN) nanoparticles films, and dielectric properties characterizations at the nanoscale. To do so, two derived modes of the Atomic Force Microscopy (AFM) are used. Peak Force Quantitative Nanomechanical Microscopy (PF-QNM) allows obtaining the interphase width, while Electrostatic Force Microscopy (EFM) measurements allow deducing the interphase relative permittivity. Based on these investigations, an electrostatic 3D model is then proposed to account for interphase properties at the microscopic scale, and to overcome the bridge between nanoscale and macroscale measurements.