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

• Published in: Journal of rheology (New York : 1978) 2010-03, Vol.54 (2), p.421-438
• Main Authors: Conrad, J. C., Wyss, H. M., Trappe, V., Manley, S., Miyazaki, K., Kaufman, L. J., Schofield, A. B., Reichman, D. R., Weitz, D. A.
• Format: Article
• Language: English
• ISSN: 0148-6055; 1520-8516
• DOI: 10.1122/1.3314295

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.