Arrested fluid-fluid phase separation in depletion systems : implications of the characteristic length on gel formation and rheology

J.C. Conrad, H.M. Wyss, V. Trappe, S. Manley, K. Miyazaki, L.J. Kaufman, A.B. Schofield, D.R. Reichman, D.A. Weitz

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Abstract

We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of =0.15–0.35. Our systems are density-matched, residual charges are screened, and the polymer-colloid size ratio is ~0.37. For these systems, the transition to kinetically arrested states, including disconnected clusters and gels, coincides with the fluid-fluid phase separation boundary. Structural investigations reveal that the characteristic length, L, of the networks is a strong function of the quench depth: for shallow quenches, L is significantly larger than that obtained for deep quenches. By contrast, L is for a given quench depth almost independent of Ø; this indicates that the strand thickness increases with Ø. The strand thickness determines the linear rheology: the final relaxation time exhibits a strong dependence on Ø, whereas the high frequency modulus does not. We present a simple model based on estimates of the strand breaking time and shear modulus that semiquantitatively describes the observed behavior.
Original languageEnglish
Pages (from-to)421-438
JournalJournal of Rheology
Volume54
Issue number2
DOIs
Publication statusPublished - 2010

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