Microscopic interpretation of granule strength in liquid media

This paper reports experimental studies illustrating the effects of partially wetting liquids on the mechanical strength of model granules composed of autoadhesive polystyrene particles. The liquids were prepared by mixing different amounts of isopropanol with pure water and their wetting behaviour was characterised by contact angle measurements on polystyrene surfaces and also by their surface tensions. The strength of the granules was measured by diametric compression while being immersed in the liquid media. The Young's modulus and yield stress were inferred from the compression data using elasto-plastic contact mechanics theory. A reduction in the granule strength was observed at a 'critical' isopropanol concentration, which was interpreted in terms of solvation forces. Existing micromechanical models of particle assemblies were examined in order to interpret the dependence of the mechanical properties on the wetting behaviour of the liquid environment. The work provides a basis for understanding some of the factors that are important in the dispersion and dissolution of granules in liquid media. (C) 2008 Elsevier B.V. All rights reserved.