On nanosilica surface functionalization using different aliphatic chain length silane coupling agents

The use of polymer nanocomposites in electrical insulation is claimed to be capable of enhancing the dielectric performance of insulation systems. This is believed to be related to the much smaller size of the filler particles, which leads to the presence of extensive interfacial areas. In this regard, nanocomposites are expected to possess unique dielectric properties that reflect the resulting interphase regions. Since the surface state of the nanofiller is closely related to the interphase regions, surface functionalization of the nanofiller has been shown by many workers to be an important factor in determining the nanocomposite´s interphase structure and, hence, the macroscopic physical properties of the system. While many comparisons of nanocomposites containing functionalized and unfunctionalized fillers have been reported, few systematic studies of this area have been undertaken with a view to understanding the mechanisms underpinning the concept of filler functionalization in nanodielectrics. In this paper, we begin to address this by using a series of functionalizing agents, which differ with respect to their aliphatic chain length; all systems were based upon trimethoxysilane and, in all cases, the nature of the thermodynamic interactions with the polyethylene matrix should be comparable. This paper reports on the effect of aliphatic chain length on the structure, breakdown and space charge behavior in the resulting nanocomposites. The possible mechanisms leading to the observed property changes are discussed.