Force‐Driven In Situ Growth of Nanostructured Silica Fillers in Polyetherimide Nanocomposites

Abstract Inorganic nanofillers have been extensively employed to tailor or enhance the properties of polymer nanocomposites, wherein the morphology of the nanofillers plays a pivotal role. Here, the use of a directional force is demonstrated to drive the in situ growth of inorganic silica nanofillers with controllable morphologies, including silica spherical nanoparticles, nanofibers, and nanosheets, within the polyetherimide (PEI) nanocomposites. The in situ grown nanofillers exhibit exceptional interfacial compatibility and uniform dispersion in the PEI matrix. Furthermore, the high aspect ratios of the silica nanofillers, combined with the interfacial effects, confer significantly enhanced mechanical strength, thermal stability, and electrical insulation upon the PEI nanocomposites, thereby unlocking substantial potential for capacitive energy storage applications. This is evidenced by the attainment of an ultrahigh dielectric energy density of 8.9 J cm −3 (150 °C) and 5.6 J cm −3 (200 °C) with an energy efficiency exceeding 90%, outperforming existing dielectric nanocomposites fabricated via conventional methods. The force‐driven growth of nanostructured inorganic fillers within polymer matrices proposes a facile and universal approach for developing high‐performance polymer nanocomposites with multi‐functionality.