Development of flexible, robust, freestanding PTFE fiber film/PTFE particles-fluorinated polyimide hierarchical sandwich composites with ultra-low dielectric constant for high-frequency applications

Abstract

Advanced flexible dielectric materials have long been sought to meet the growing demands of high-frequency and high-speed applications. Herein, a composite system was first synthesized by blending water-soluble fluorinated poly (amic acid) ammonium salt (FPAAs) with polytetrafluoroethylene particles (PTFE_P), namely PTFE_P-FPAAs. Then, unique and freestanding PTFE_F/PTFE_P-fluorinated polyimide (FPI) composite sandwich films (50–90 μm thick) combining PTFE fiber film (PTFE_F) core with PTFE_P-FPI film sheets were fabricated via a facile layer-by-layer process. The dielectric, thermal, mechanical, and hydrophobic properties of the proposed composite films were systematically investigated. The optimal performance achieved by the PTFE_F (30 vol%)/PTFE_P (40 vol%)-FPI sandwich film in the high-frequency range (8.2–12.4 GHz and 12–18 GHz) present an ultra-low dielectric constant of 1.84 (at 10 GHz), dielectric loss factor of 0.005, and dielectric strength of 213.0 kV/mm. Theoretical analyses employing coupled dielectric constant and dipole polarization models, provided further insights into the observed dielectric behavior. The incorporation of PTFE_F, PTFE_P, and the sandwich structure synergistically enhanced the dielectric performance. Additionally, a large-deformation (15 % and 45 % compressive strain) cyclic buckling test was conducted to evaluate the mechanical robustness of the sandwich films. This work demonstrates a solid experimental and theoretical foundation for the development of advanced dielectric composite materials.