CONTACT-ANGLE, ADSORPTION AND WETTABILITY - A REVIEW WITH RESPECT TO POWDERS

The significance of wettability, polarity and surface energy of powders with respect to their usage is discussed in terms of spreading coefficients. Indications as to how surface energies can be used to predict interactions are given. The techniques for measuring contact angles of powders have been reviewed critically. Vapour adsorption is a critical stage in the wetting process and a good deal of information can be obtained from its study. The application of the techniques of adsorption microcalorimetry, a vacuum microbalance and dielectric spectroscopy are outlined. By use of dielectric spectra and the thermodynamic parameters of adsorption, it is possible to attempt a description of the mechanism of the wetting process. The use of thermodynamic functions of immersion is also discussed. The role of changes in molecular structure and of different forms of physical treatment (i.e., milling) in controlling the wetting of powders is considered and pointers to further work are given. © 1990.