Evaluation of Dynamic Hydrophobicity Behavior of Silicone Rubber Insulators Filled With 2D Nanosheets Using a Direct Current Dynamic Drop Test

The growing use of composite polymer insulators in high-voltage direct current (HVDC) transmission systems requires a thorough understanding of their dynamic hydrophobicity characteristics to ensure long-term reliability. This study investigates the retention, recovery, and transfer of hydrophobicity in silicone rubber (SiR) composites filled with two-dimensional (2D) nanosheets, specifically molybdenum disulfide (MoS₂) and tungsten disulfide (WS₂), under DC Dynamic Drop Test (DDT) conditions. The efficacy of these fillers is evaluated against traditional alumina trihydrate (ATH) and fumed silica (SiO₂) fillers. The Weibull probability analysis of the hydrophobicity retention test indicates that MoS₂-filled composites achieved the highest hydrophobicity retention time (773.4 min), representing a 324.3% increase compared to the unfilled sample (185.4 min), while WS₂ composites showed a 223.1% increase (609.7 min). In terms of hydrophobic recovery after 24 hours, MoS₂ composites demonstrated a 282.6% improvement (125.6 min), followed by WS₂ with a 160.4% improvement ( η =87.1 min) relative to the unfilled reference (33.9 min). The hydrophobicity transfer test showed that fumed silica promoted faster low molecular weight (LMW) migration, while MoS₂ and WS₂ slowed LMW diffusion due to stronger filler-matrix interactions. Experimental improvements-such as optimized sample preparation, electrolyte control, and voltage ramping-significantly reduced test variability, improving DDT reproducibility. The findings confirm that MoS₂ and WS₂ nanosheets substantially enhance the long-term hydrophobic stability of SiR composites under HVDC stress, highlighting their suitability for outdoor insulation applications.