Abstract
PTFE-based microwave composites filled with SiO2 dielectric ceramic (PTFE/SiO2) were prepared by powder processing technique followed by hot pressing. The effects of compound coupling agent on the contact angle and surface energy of SiO2 filler, as well as moisture absorption, dielectric properties, temperature coefficient of dielectric constant (τ e ) and coefficient of thermal expansion (CTE) of the PTFE/SiO2 composites were investigated. The content of SiO2 in PTFE/SiO2 composites was maintained as 57 wt%. SiO2 powders were pre-treated by the mixture of phenyltrimethoxysilane (Z6124) and aminopropyltriethoxysilane (KH550) coupling agents before mixing and reacting with PTFE. The compositions of the coupling agents mixture are x% KH550 + (1.5 − x)% Z6124 (x: mass ratio to SiO2, x = 0, 0.15, 0.3, 0.45, 0.6, 0.75, 1.5). The results show that as the content of KH550 and Z6124 is 0.3 and 1.2 wt%, respectively, the modified SiO2 filler has a maximum value of contact angle, at the same time the composites achieve a most compact structure with a maximum density of 2.031 g/cm3. Moreover, improved properties, including dielectric constant (e r ) of 2.83, dielectric loss (tan δ) of 7.4 × 10−4, CTE of 28.81 ppm/°C and temperature coefficient of dielectric constant (τ e ) of 22.8, are obtained. The ratio of experimental and theoretical dielectric constant values is 96.97%. It has been found that the compound coupling agent (KH550 and Z6124 are 0.3 and 1.2 wt%, respectively) results in improved performance of the composites than that of previous reported work.
Published Version
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