Dynamic mechanical properties were studied for epoxy resin filled with porous silica microballoons with varying surface area, pore radius, pore volume and adsorbed water. The glass transition temperature (Tg) of the composites is 12–14°C lower than the Tg of the unfilled epoxy resin. This Tg depression is attributed to the preferential adsorption of curing agents on the porous silica microballoons. Tg of the composite increases with increase in the adsorbed water on fillers. The storage modulus has a distinct correlation with the Hg‐surface area of silica microballoons, which corresponds to the sum of the surface area of pores with radii larger than about 4 nm. Tan δc tan δm decreases with increasing Hg‐surface area. © 1991 Hüthig &amp
Wepf Verlag, Basel