Abstract:
Nano/micro ceramic-filled epoxy composite materials have been processed with various percentage additions of SiO2, Al2O3 ceramic fillers as reinforcements selected from the nano and micro origin sources. Different types of filler
combinations, viz. only nano, only micro, nano/micro, and micro/micro particles, were designed to investigate their
influence on the thermal expansion, thermal conductivity, and dielectric properties of epoxy polymers. Thermal
expansion studies were conducted using thermomechanical analysis that revealed a two-step expansion pattern
consecutively before and after vitreous transition temperatures. The presence of micro fillers have shown vitreous
transition temperature in the range 70–80°C compared with that of nano structured composites in which the same
was observed as ~90°C. Similarly, the bulk thermal conductivity is found to increase with increasing percentage of
micron-size Al2O3. It was established that the addition of micro fillers lead to epoxy composite materials that
exhibited lower thermal expansion and higher thermal conductivity compared with nano fillers. Moreover, nano
fillers have a significantly decisive role in having low bulk dielectric permittivity. In this study, epoxy composites
with a thermal expansion coefficient of 2.5 × 10 5/K, thermal conductivity of 1.18W/m· K and dielectric permittivity
in the range 4–5 at 1 kHz have been obtained. The study confirms that although the micro fillers seem to exhibit
good thermal conductivity and low expansion coefficient, the nano-size ceramic fillers are candidate as cofillers
for low dielectric permittivity. However, a suitable proportion of nano/micro-mixed fillers is necessary for achieving
epoxy composites with promising thermal conductivity, controlled coefficient of thermal expansion and dielectric
permittivity.
