Characterising and Killing the Exciting Rheology of Concentrated Suspensions
A.M. Howe, J.H.E. Hone, A.R. Pitt and T.J. Wear
Kodak European Research, UK
rheology, concentrated suspension, anistropic particles, dispersant, rheology modifier, shear thickening, jamming, switching
Invited lecture. Industrial applications of boehmite include: paint and coating materials, sol-gel ceramics, rheology modifiers, polymer additives, abrasives, refractory materials, and catalysts. Catapal 200 comprises intergrown 40nm boehmite crystallites that are highly anisotropic. Catapal 200 powder disperses readily in water to give a suspension of pH 4 in which the particles have a cationic surface charge. The rheological behaviour of concentrated suspensions of Catapal 200 is novel and includes irreversible shear thickening and subsequent, reversible switching between jammed and high-viscosity states. The above behaviours could make Catapal 200 one of the less popular materials in a manufacturing environment. Once characterized, the scientific challenge is to remove the excitement from the rheological behaviour without diluting the suspension. No commercial dispersant was successful, and many increased the shear sensitivity of the suspensions. To address this challenge, a series of novel ‘FAB’ dispersants was designed: Functional molecules with a strongly adsorbing Anchor group and an oligomeric, water-soluble Buoy. Only these dispersants were successful in removing the irreversible shear-thickening behaviour of the boehmite suspension and they also gave the added benefit of a reduction in viscosity. This new class of dispersants has been found to be effective in controlling or removing yield stress in suspensions of other cationically charging inorganic colloids.
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Nanotech 2007 Conference Program Abstract