Influence of Moisture Absorption and Nano-SiO ₂ Doping on Dielectric Properties and Space Charge Accumulation in PDMS

Dielectric elastomers (DEs) with compliant electrodes are widely employed in polymeric energy transducers. An example of the use of DEs is in ocean wave energy conversion, where the potential energy of the waves is directly converted into electrical energy. Inevitably, the DE materials will be exposed to sea water, which may hamper the mechanical and electrical properties and hence the service life. Moreover, when such a system is energized by a high DC voltage, space charge transport may distort the electric field distribution in the dielectric, with a potentially negative effect on breakdown performance. In this paper, polydimethylsiloxane (PDMS) and PDMS/SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanocomposites were prepared using a commercial DE material. The nanocomposites contained a small weight percentage of nanosilica, surface-treated and non-surface-treated. The samples were put in a climate chamber with high humidity (97%) at 56.5°C to absorb moisture for different amounts of time. To accelerate the water uptake of the films, some samples were immersed in deionized water or prepared seawater. The effect of water absorption on the dielectric properties of PDMS and PDMS/SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanocomposites is discussed and the space charge characters under different applied DC electric fields are analyzed using the pulsed electro-acoustic method (PEA). The results show that the introduction of nano silica improves the dielectric properties of PDMS, reducing charge accumulation and leading to very little distortion of the electric field distribution even after water uptake. In both PDMS and PDMS/SiO<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> nanocomposites, water absorption leads to increasing dielectric losses and conductivity, accompanied with a decrease of 50 Hz AC and DC breakdown strength. It is shown that an increasing charge carrier mobility results in a larger charge accumulation and a more distorted electric field in the wet samples.