The rheological behaviour of a 58 vol.% dispersion of styrene/acrylate particles in ethylene glycol was investigated using a plate-on-plate rheometer. Experimental results showed that the concentrated polymer dispersion exhibited a strong shear-thickening transition under both steady shear and dynamic oscillatory conditions. The low-frequency dynamic oscillatory behaviour could be reasonably interpreted in terms of the steady shear behaviour. Accordingly, the critical dynamic shear rate [(g)dot]textc_d , dot{gamma }_{{{text{c_d}}}} , agreed well with the critical shear rate obtained in steady flow [(g)dot]textc_s , dot{gamma }_{{{text{c_s}}}} , where [(g)dot]textc_d dot{gamma }_{{{text{c_d}}}} was calculated as the maximum shear rate by the critical dynamic shear strain γ c and the frequency ω, i.e. [(g)dot]textc_d = wgtextc . dot{gamma }_{{{text{c_d}}}} = omega gamma_{text{c}} . However, during high-frequency dynamic oscillation, it was observed that the shear thickening occurred only when an apparent critical shear strain was reached, which could not be fully explained by the wall-slipping effect. Based on freeze fracture microscopic observations, the effect of the micro-sized flocculation of particles on the rheology of concentrated dispersions was also discussed.
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