Improved dispersion and interfacial interaction of SiO2@polydopamine fillers in polytetrafluoroethylene composites for reduced thermal expansion and suppressed dielectric deterioration

Copper-clad laminate (CCL) comprised of copper foil and polytetrafluoroethylene (PTFE) faces severe thermal expansion mismatch due to the discrepancy in coefficient of thermal expansion (CTE) between the two components. Incorporating inorganic fillers with low CTE into PTFE has been proved to be a promising way to achieve the goal. However, it is a challenge to achieve homogeneous distribution and good interfacial interaction of fillers in PTFE composites owing to the characteristics of PTFE emulsion. In this work, core@shell structured SiO2@polydopamine fillers (SiO2@PDA) were synthesized and incorporated into PTFE matrix to form SiO2@PDA/PTFE composites. Due to the presence of PDA shell, SiO2@PDA exhibited improved dispersion and interfacial interaction, contributing to the reduced CTE and suppressed dielectric deterioration of SiO2@PDA/PTFE composites. With 40 vol% of filler, the CTE of SiO2@PDA/PTFE composite was efficiently reduced (50%), coupled with a limited sacrifice of only 2% and 40% of increments for dielectric constant (Dk, 2.3) and dielectric loss (Df, 2.4 × 10−3), respectively (@40 GHz), as compared with that of the corresponding SiO2/PTFE composite. The fillers and composites were comprehensively characterized to verify the mechanism of CTE and dielectric properties of the composites.