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Experimental studies and theoretical explanations were carried out in order to understand the influence of moisture absorption on the dielectric properties of magnesium oxide (MgO)/low density polyethylene (LDPE) nano-composite. After exposing LDPE and our MgO/LDPE to 40% relative humidity (RH) for 9 days, the absorbed water content in LDPE and our MgO/LDPE nanocomposite was about 2.3? and about 3.6? respectively. Experimental results show that moisture absorption has a negative influence on the dielectric properties of our MgO/LDPE nanocomposite at high electric fields of about 40kV/mm. Damp nanocomposites can still maintain the ability to suppress space charge and keep the conducting current from increasing (which normally occurs when moisture is absorbed) at low electric fields below 20 kV/mm. Absorbed water molecules can be considered to be divided into three forms, free water molecules which are assumed into the polymer matrix, weakly bound water molecules which may gather around nano-particles and tightly bonded water molecules, bound by hydrogen bonds. Thermogravimetry (TG) test results indicate that tightly bonded water molecules cannot be removed from the nanocomposite after a drying process at 80 °C in vacuum conditions. For damp MgO/LDPE nanocomposite after the drying process, the j-E characteristics were completely recovered up to an electric field of 40 kV/mm, whereas the space charge suppression ability partially recovered. The reason for this partial recovery may be attributed to the influence of tightly bonded water molecules on the interfacial charge in nano-particles and matrix polymers. [ABSTRACT FROM PUBLISHER]

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. [ABSTRACT FROM AUTHOR]