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

Abstract

Linear viscoelastic properties of SiO2/(AP/EP) suspension with various SiO2 volume fractions (ϕ) 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 (ϕ ≤ 30 vol.%) to viscoelastic solid (ϕ ≥ 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 ϕ ≅ 35 vol.% and T ≅ 100°C characterized with a power–law relationship between the storage and loss moduli (G ′ and G ″) and frequency (ω); G ′ = G ″/tan(nπ/2) ∝ ω n . The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.