Effects of perfluorooctyltriethoxysilane coupling agent on the properties of silica filled PTFE composites

摘要

Fused amorphous SiO_2 filled polytetrafluoro-ethylene (PTFE) microwave substrate composites were manufactured. The composition of all the samples was 57 wt% SiO_2 and 43 wt% PTFE. The effects of compound silane coupling agents on the properties of the SiO_2 filled PTFE composites were investigated, including density, water absorption, dielectric properties and temperature coefficient of dielectric constant. Compound coupling agents x wt% KH550+ (1.5-x) wt% F8261 (x: mass ratio to SiO_2 ceramic, x = 0, 0.2, 0.4, 0.6, 0.8, 1.0) were used to pre-treat SiO_2 fillers and the performance of composites were improved with appropriate amounts of coupling agents. The SEM results show that SiO_2 particles modified with compound coupling agents are well dispersed in PTFE polymer and exhibit a strong connection with PTFE. The dielectric constant of all the composites shows excellent frequency stability within the frequency from 1 to 18 GHz. The SiO_2 ceramic filler modified with 1.1 wt% F8261 and 0.4 wt% KH550 simultaneously has the highest contact angle and the lowest surface energy, besides, the composite achieves a most compact structure with a maximum density of 2.059 g/cm3. At the same time, this composite obtains optimal properties, including good dielectric properties (ε_r~2.89, tanδ~0.0007), acceptable water absorption of 0.2%, temperature coefficient of dielectric constant (τ_ε) of 32.32 ppm/℃. Moreover, the ratio of experimental and theoretical dielectric constant can achieve 98.86%, which is far greater than that in previous reports.