Silica Functionalization: How Does it Affect Space Charge Accumulation in Nanodielectrics Under DC?

Functionalization of silica nanoparticles with polar aminosilane and its effect on space charge accumulation under high voltage direct current (DC) was studied in polypropylene (PP)/ Ethylene-Octene Copolymer (EOC) /silica nanodielectrics. The modification reaction conditions were varied in order to alter the deposited layer grafting density and morphology, and hence, the filler-polymer interfacial properties. The effect of this alteration was then studied on the space charge accumulation under a high DC field as one of the most important properties to tune for HVDC cable insulation systems. The chemical modification of the silica surface was first confirmed via Thermogravimetric Analysis (TGA) and Fourier Transform IR Spectroscopy (FTIR). Differential Scanning Calorimetry (DSC) was performed on the nanocomposites to study the effect of the nano-engineered interfacial areas on nucleation and crystal formation. The effect of the amine functional groups on the charge carrier trapping and transport in this insulation system was studied via Thermally Stimulated Depolarization Current (TSDC) method.It was argued that the amine functionality on the silica surface can induce deep trap states at the filler-polymer interfaces, and hinder further injection of the space charge. Under certain modification conditions, the aminosilane can form 'island-like' structures on the silica surface. These islands can both facilitate nucleation, inducing transcrystallization at the filler-polymer interface, and further contribute to the induction of deep traps which result in reduction of space charge accumulation in the nanodielectric.