Hollow silica@nanodiamond core-shell hybrid fillers for constructing polytetrafluoroethylene composites with low dielectric constant and enhanced thermal conductivity

Hollow silica microspheres (HSM) can effectively reduce the coefficient of thermal expansion (CTE) of polytetrafluoroethylene (PTFE) while maintaining low dielectric constant (D k ) of the composites. However, the incorporation of HSM often leads to a decrease in thermal conductivity (TC). To overcome this limitation, we developed a multifunctional hybrid filler by coating nanodiamonds (ND) onto HSM surfaces (HSM@ND) via an electrostatic self-assembly process, and subsequently incorporating it into the PTFE matrix to fabricate HSM@ND/PTFE composites. Benefiting from the rough surface, HSM@ND exhibits enhanced interfacial interaction with PTFE, which significantly improves the CTE suppression efficiency of the composites. Meanwhile, the ND shell forms thermally conductive pathways, substantially increasing TC, and the encapsulated air within HSM contributes to the low D k . As a result, the composite with 30 vol% HSM@ND achieves a lower CTE of 76 ppm °C −1 , a 92.8 % increase in TC compared with HSM/PTFE composites, while maintaining a low D k of 2.01 and dielectric loss (D f ) of 0.0013. This work provides an effective strategy to design PTFE-based dielectric composites that combine low CTE, improved TC, and excellent dielectric properties.