Liquid penetration as a method of assessing the wettability and surface energy of pharmaceutical powders.

The use of a liquid penetration technique to assess the wettability and surface energy of a series of barbiturates, including the use of bicomponent systems, has been critically evaluated. Values of apparent contact angles (theta) obtained using the Washburn relationship (1921) and the Carli & Simioni correction (1979) were found to reflect the practically derived wettability of the powders. Values of gamma c obtained from modified Zisman plots and from Neumann's equation of state did not realistically describe the surface energies of the powders. The nature of alcohol-water mixtures has been examined to assist elucidation of the theoretical problems associated with the technique and to offer a possible explanation for the inadequacies of the surface energy results.