Abstract
Rheological properties of aqueous suspensions and rheometry for viscoelastic measurements over a wide range of frequency were investigated. The raised cosine pulse method for the measurements was improved by using rectangular pulse strain including high-frequency Fourier components. For further extension of the frequency range, a new rheometer was also developed on the basis of the surface loading method. These methods as well as a conventional dynamic method were utilized to determine rheological properties of aqueous solutions of an end-associating polymer (suspending media for resin particles). The relaxation behavior of these solutions was in good agreement with predictions of the Tanaka theory for transient networks. Aqueous suspensions of poly(acryl-co-styrene)(AS) particles with radius a0=45nm showed linear viscoelastic relaxation behavior, and the time-volume fraction superposition was found to be valid. In the linear regime, AS particles behaved as the Brownian hard particles having an effective radius aeff = a0 + ξ with ξ being a thickness of the electric double layer, and the dependence of their zero-shear viscosity η0 on an effective volume fraction φeff (= {aeff /a0}3 φ ) agreed with the dependence of η0 of ideal silica suspensions on the bare volume fraction φ . In the range of φeff < φ m (φ m ; random close packing volume fraction), η0 was well described by the Brady theory for Brownian particles. In the range of φeff > 0.6, a repulsive force due to overlapping electric double layers also contributed to the viscoelastic behavior of AS suspensions. In aqueous suspensions of polystyrene (PS) particles, flocculation and sedimentation of PS particles occurred on addition of a small amount of the associating polymer. Analysis of the polymer conformation at the particle surface suggested that the polymers formed interparticle bridges thereby inducing of the flocculation and sedimentation.
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