Effect of surface modification of SiO₂ on properties of highly filled SiO₂/polytetrafluoroethylene composite films

Three silane coupling agents with different hydrophobic groups, namely phenyl-containing coupling agent 1(Ph-1), fluorine-containing coupling agent 2(F-2) and a glycidoxy-containing coupling agent 3(GP-3) were used to modify SiO₂. The SiO₂/polytetrafluoroethylene(PTFE) composite films with 35wt% SiO₂ and thickness of 50 μm were prepared by air-assisted dry blending, cold-pressing, sintering and skiving techniques. The dispersion of SiO₂ throughout the PTFE matrix is uniform after the modification. The effects of F-2 contents on the properties of SiO₂/PTFE composite film were studied. The results show that when the content(mass ratio to SiO₂) of the coupling agent is 0.3%, the pinhole defects of SiO₂/PTFE composite film are rarely observed, and the tensile strength increases from 9.2 MPa to 16.2 MPa. Meanwhile, the dielectric constant decreases from 2.475 to 2.416 at 10 GHz, and the dielectric loss decreases from 2.66×10⁻³ to 2.01×10⁻³, exhibiting improved dielectric properties.