Assessment of nano dielectrics interface charge by electrokinetic sonic amplitude and atom force microscopy

Research has predicted the existence of the interface charges between nano particles and matrix polymers in nano dielectrics, which may become a dominant factor as the electrical properties of composites continue to improve. But until now, no experimental evidence has been found to prove this prediction. This research try to prove that the charging abilities of the nano particles in liquid suspension are related to that of polymeric nanocomposites, even more to find the existence evidence of interface charge in polymeric nanocomposites. Zeta potential of surface modified nano particles SiO₂, and MgO/ paraffinic wax suspension systems have been measured by electrokinetic sonic amplitude (ESA) method to assess the charging properties. The average of zeta potential value of -62.8 mV and 2.1 mV of SiO₂, and MgO/ wax suspension systems were obtained. The interface charge domains were detected by means of atomic force microscopy (AFM) lift model phase scanning of atomic flat surface of the corresponding polymeric nano composites. The interface charge domains have been found in SiO₂/ low density polyethylene (LDPE) nanocomposite but cannot be found in MgO/LDPE system, which agree with the tremendous deference of zeta potential of corresponding suspension. Three types of models are proposed to interpret the AFM phase scanning appearance of the domains. Measurement results of zeta potential and AFM phase scanning and j (current density)-E (electric field) characteristics of LDPE and two kinds of nano composites reveal that the interface charge zones would inhibit the conducting current densities of the composites, and the larger absolute value of zeta potential corresponds to the stronger inhibiting ability to the conducting current density in polymeric nanocomposites.