Investigation of charge injection in PDMS/SiO2 nanocomposites using the combined measurement method

Abstract

Dielectric elastomers (DEs) assembled with compliant electrodes are widely utilized in polymer-based energy transducers. Under high DC voltage, space charge accumulation within DEs can result in significant electric field distortion inside the dielectrics and at the electrode/insulation interfaces. This phenomenon is recognized as a critical factor influencing dielectric breakdown, aging characteristics, and, consequently, the long-term operational reliability of energy conversion systems. The formation and transport of space charge are governed by charge injection and extraction processes at the electrode interfaces. Previous studies have demonstrated that doping polydimethylsiloxane (PDMS) with nanosilica particles can effectively suppress space charge accumulation and enhance breakdown strength. In this paper, the charge injection behavior of PDMS/SiO2 nanocomposites with varying filler concentrations was investigated based on simultaneous measurements of space charge and conduction current using a double-layer structure. The experimental results reveal a linear relationship between the square root of the electric field intensity and the logarithm of the injection current at the electrode/PDMS interface across all samples. From this relationship, key parameters, such as the injection barrier (Φ) and the field-enhancement coefficient (β), were extracted. Compared with neat PDMS, the nanocomposites exhibited lower injection barriers, indicating a reduced rate of charge injection due to the incorporation of silica nanoparticles, which partially explains the observed suppression of space charge under high DC fields. Moreover, nanocomposites containing surface-treated silica showed similar β values to the undoped PDMS while exhibiting lower injection barriers, which is beneficial for improving both conduction behavior and dielectric breakdown strength under high electric fields.