Surface modified hollow glass microspheres-epoxy composites with enhanced thermal insulation and reduced dielectric constant

The hollow glass microspheres (HGMs) are the important fillers in the thermal insulating composites due to the low density, high flowability and the low thermal conductivity. However, the high filling ratio of HGMs without phase separation is hard to be reached owing to the weak interface binding strength between the HGMs and the resin matrix in the composites. In this work, the surface of HGMs is modified with silane coupling agents (3-Glycidoxypropyltrimethoxysilane, KH560) to improve the interface binding strength. After the surface modification, the maximum filling ratio of the HGMs in the epoxy (EP) resin can reach 35 wt. % (67 vol. %). The highly improved filling ratio benefits the HGMs-EP composites with an improved thermal insulation with a low thermal conductivity 0.14 W·m−1·K−1. Moreover, a highly reduced permittivity Dk = 2.3 at the frequency of 110 MHz is also attained for the 67 vol. % HGMs filled composites, which should be promising for the 5G communication technology that requires low dielectric constant for reducing the signal delay and loss.