Effect of micro- and nano-fillers on the properties of silicone rubber-alumina flexible microwave substrate

Silicone rubber composites filled with micro- and nano-alumina were prepared and the effect of filler contents on the microwave dielectric, mechanical, thermal and moisture absorption properties were investigated. The composite with 0.45 volume fraction (V-f) of micro alumina has a relative permittivity (epsilon(r)) of 5.89 and dielectric loss (tan delta) of 9 x 10(-3) whereas 0.05 volume fraction of nano-alumina has epsilon(r) of 3.52 and tan delta of 1.97 x 10(-2), respectively at 5 GHz. The experimental epsilon(r) and tan delta values of silicone rubber-micro-alumina composites were compared with that of theoretical models. Among the theoretical models Modified Lichtenecker and Parallel model are in good agreement with experimental values of epsilon(r) and tan delta respectively. The silicone rubber nano-alumina composites have better mechanical properties. The coefficient of thermal expansion (CTE) of composites decreased and the moisture absorption increased with increasing amount of filler loading. The improved properties indicate that the silicone rubber-micro-alumina composite is a good candidate for a flexible microwave substrate application. 2013 Elsevier Ltd and Techna Group S.r.l. All rights reserved.