Introduction
Powders such as food ingredients, pharmaceuticals, dyes, fertilizers, a.s.o., are frequently dispersed and/or dissolved in water or an aqueous liquid in the course of an industrial process or before use. The behaviour of a powder under such treatment is, of course, governed by the forces interacting between the individual particles.
A process in which a dispersion or solution is created involves powder particles in the dry state, in the wetted state, and (a small fraction at any given point in time) particles which are just about to be wetted, i.e., particles penetrating the gas/liquid interface. During wetting, the interaction forces between the particles change significantly. If the material is partly or fully soluble, the properties of the dispersant may also vary. The rate at which a powderous material can be immersed in a continuous or batchwise dispersing process therefore depends on a large number of physical properties. So far, no theory exists which allows the prediction of the powder dispersion rate based on such properties and the type of apparatus employed for the process.
Nevertheless, knowledge of the interaction forces is indispensable for understanding how to influence certain powder properties so that the product is easier to disperse. Quite a lot of work has been performed in the field of powder “instantization”, especially in the food industry and in food related research. Here, certain powder properties termed “instant properties” have been defined, measuring methods have been developed, and technical processes for the instantization of powders exist. All this is closely related to adhesion forces, since agglomeration plays the most important role in this field.