<scp> 2D WS ₂ </scp> /Polyimide Composite Films With Enhanced Mechanical Properties, Electrical Breakdown Strength, and Thermal Stability via Optimized Filler–Polymer Interfaces

ABSTRACT Polyimide (PI) has been extensively employed in flexible insulation applications for electrical equipment due to its exceptional mechanical properties, thermal stability, and superior electrical insulation performance. This study employed two‐dimensional (2D) tungsten disulfide (WS 2 ) with varying surface dimensions and thickness to modify PI for the first time, exploring the mechanism of the interfacial effect of WS 2 in the matrix on the performance enhancement of composite films. The 2D WS 2 , owing to its low interlayer friction characteristics and the formation of a continuous interfacial phase within the polymer matrix, facilitates efficient stress transfer between the filler and matrix. Additionally, the high thermal conductivity of WS 2 mitigates localized overheating, which in turn increases the thermal decomposition temperature of the polyimide film. Moreover, the uniformly dispersed lamellar architecture introduces a high density of interfacial charge traps; the confinement effect of these traps on the charge effectively inhibits the development of discharge channels. The WS 2 /PI composite film prepared by in situ polymerization shows excellent performance, with significant increases of 162.9% in elongation at break and 12.8% in breakdown strength. This work provides critical insights into the design and preparation of advanced flexible insulating materials for high‐voltage electrical applications.