This study introduces a new core-shell structured polytetrafluoroethylene (PTFE)/polyimide (PI) nanoparticle for additive manufacturing of microwave substrates. Materials were synthesized using a solution processed method through the electrostatic interaction between PTFE with negative potential and poly(amic acid) salt (PAAS, a PI precursor) with positive potential followed by the thermal imidization of PAAS. Microscopic studies by transmission electron microscopy, scanning electron microscopy, and atomic force microscopy confirmed the formation of core-shell nanoparticles, a porous material network, and a reduction of surface roughness upon imidization. In addition to excellent high temperature stability (<0.4% weight loss at 500 8C), the synthesized materials showed improved particle-to-particle adhesion and particle-to-substrate adhesion compared to PTFE alone, and good dielectric properties measured at 7.2 GHz utilizing a cavity perturbation technique. The materials consisting of 5% to 35% of PI exhibited low relative permittivity (E 0 ) of 2.14 to 2.38 and loss tangent (tan d) of 0.001 to 0.0018, which make them well suited for use in additive manufacturing.

Few studies have examined the deposition of polytetrafluoroethylene (PTFE) using additive manufacturing and their subsequent properties in microwave devices. The present study examines polytetrafluoroethylene-polyacrylate (PTFE-PA) composite films made via aerosol deposition to assess the potential use of PTFE in additive manufacturing processes. The composites are composed of PTFE-PA core − shell nanoparticles, synthesized using a seeded emulsion polymerization, containing various PTFE weight fractions up to 50%. The synthesized nanoparticles were sprayed onto a heated glass substrate and subsequently annealed at a temperature above the glass transition temperature of PA and below that of PTFE, rendering a solid film approximately 40 m thick. A cavity perturbation resonance technique was employed to determine the complex permittivity of the films. As the volume fraction of PTFE increased, the real part of the permittivity ′ decreased while the imaginary part of the permittivity ′′ showed little variation. The results demonstrate a promising approach for incorporating PTFE into additive manufacturing processes, particularly for microwave devices.