Rheology of SiO2/(acrylic polymer/epoxy) suspensions. I. Linear viscoelasticity

Linear viscoelastic properties of SiO2/(AP/EP) suspension with various SiO2 volume fractions (I center dot) in a blend of acrylic polymer (AP) and epoxy (EP) were investigated at various temperatures (T). The AP/EP contained 70 vol.% of EP. The SiO2 particles were treated with epoxy silane coupling agent. The effects of the SiO2 particles are more pronounced in the terminal zone: a transition from viscoelastic liquid (I center dot a parts per thousand currency signaEuro parts per thousand 30 vol.%) to viscoelastic solid (I center dot a parts per thousand yenaEuro parts per thousand 40 vol.%) was observed which can be interpreted as a critical gelation occurring at a critical particle content and critical gel temperature. The SiO2/(AP/EP) systems exhibited a critical gel behavior at I center dot a parts per thousand...aEuro parts per thousand 35 vol.% and T a parts per thousand...aEuro parts per thousand 100A degrees C characterized with a power-law relationship between the storage and loss moduli (G (') and G (aEuro3)) and frequency (omega); G (') = G (aEuro3)/tan(n pi/2) aeaEuro parts per thousand omega (n) . The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.