Faculté des sciences

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

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

In: Journal of Rheology, 2010, vol. 54, no. 2, p. 421-438

We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of Φ=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... Plus

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    Summary
    We investigate the structural, dynamical, and rheological properties of colloid-polymer mixtures in a volume fraction range of Φ=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 Φ; this indicates that the strand thickness increases with Φ. The strand thickness determines the linear rheology: the final relaxation time exhibits a strong dependence on Φ, 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.