Optical properties of chemicals 19. Materials in this context can be solids, liquids or gases. Perry discusses the some aspects of the behaviour of gases, and Ullmann discusses elastic solids. When liquids are subjected to stress they will deform irreversibly and flow. Non-ideal examples would be toothpaste or cornflour mixed with a little water.
Examples are toothpaste and whipped cream.
Such liquids display increasing viscosity with increasing shear. Examples are wet sand, and mixtures of starch powder with small amounts of water. This property is extremely important in industrial products, e.g to prevent settling of dispersed solids on storage. A stiff paste slurry of maize or cornflour in water can appear to be quite liquid when swirled around in a cup. It should be noted that the study of viscosity and flow behaviour is extremely complex.