Rheology of SiO2/(Acrylic Polymer/Epoxy) Suspensions. I. Linear Viscoelasticity

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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) ∝ ωn. The critical gel exponent (n) was estimated to be about 0.45. The gelation occurred with increasing T.