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SYGK: Symposium Rheologische Eigenschaften von Polymersystemen
SYGK 2: Symposium
SYGK 2.4: Vortrag
Montag, 1. März 1999, 17:25–17:50, HS 19
Rheology of highly concentrated, bimodal dispersions with colloidal interactions — •N. Willenbacher, B. Morrison, and B. Dames — BASF AG, Polymer Research Laboratory, D-67056 Ludwigshafen
The relationship between particle size distribution and viscosity of concentrated dispersions is of great industrial importance, since it is the key to get high solids dispersions or suspensions. The problem is treated here experimentally as well as theoretically for the special case of strongly interacting colloidal particles. An empirical model based on a generalized Quemada equation ηR = (1−φ/φmax)−є is used to describe η as a function of volume fraction φ for mono- as well as multimodal dispersions. The exponent є characterizes the interactions among the particles. Starting from a limiting value of 2 for non-interacting either colloidal or non-colloidal particles є generally increases strongly with decreasing particle size. Model calculations as well as experiments show, that the viscosity of the dispersion varies not only with the size ratio of large to small particles, but also depends on the absolute particle size. Especially, the well-known viscosity minimum for bimodal dispersions with volumetric mixing ratios of around 30/70 of small to large particles vanishes if colloidal interactions contribute significantly. The experimentally determined φmax values agree very well with predictions from an empirical expression for suspensions with arbitrary particle size distribution (Sudduth, J. Appl. Polym. Sci. 48 (1993)) extracted from a large number of literature data related to non-colloidal suspensions.