Temperature induced gelation of concentrated ceramic suspensions:: Rheological properties

Concentrated sterically stabilised ceramic suspensions have been reversibly gelled by changing the temperature. Using an amphiphilic polymer, Hypermer KD3, as dispersant for alumina and alumina-silicon carbide whisker composite mixtures in pentanol resulted in a transition from dispersed to flocculated stare close to room temperature. The collapse of the adsorbed polymer layer with decreasing solvency (temperature) in the marginal solvent pentanol induces flocculation when the long-range van der Waals force overcomes the remaining steric repulsion. Temperature induced gelation (TIG) of concentrated suspensions has a drastic effect on the rheological properties. At temperatures above 30 degrees C, the suspensions have a low viscosity and negligible elasticity. When the temperature is lowered below 20 degrees C, the viscosity increases significantly and the viscoelastic behaviour becomes predominantly elastic. The elasticity and the associated particle network strength are sufficiently high for a highly concentrated gelled suspension to support its own weight. The potential use of TIG as a novel forming method was discussed with relation to other new shaping techniques. (C) 1999 Elsevier Science Limited. All rights reserved.