In recent years, polysiloxane dielectric elastomers (DEs) have attracted extensive attention, but their low dielectric constant and electrical breakdown strength are the main factors that limit their wide application. In this work, we report the effects that a high content of hydrophobic silica has on the dielectric properties and dielectric relaxation behavior of polymethylphenylsiloxane (PMPS). Introducing a high content of hydrophobic silica into PMPS composites increased the dielectric constant of PMPS composites from 3.11 to 3.70 and the breakdown strength of PMPS composites from 35.31 to 42.66 kv/mm. The high content of hydrophobic silica is beneficial for restraining or delaying the occurrence of direct current (DC) conductivity and for effectively reducing the dielectric loss of composites in high temperature and low-frequency regions. The high content of hydrophobic silica also produces interfacial polarization in the composites, and this increases the dielectric constant and dielectric loss in the high frequency and low-temperature regions. The dielectric relaxation behavior of PMPS composites was studied in detail using broadband dielectric spectroscopy (BDS) and thermally stimulated depolarization current (TSDC) to better understand the effect of hydrophobic silica on dielectric properties. This work opens a new way to design and prepare polysiloxane-based materials that have a high dielectric constant, low dielectric loss, and high breakdown strength.
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