UCL Discovery

Abstract

The value of contact angle measurements on compressed discs of powder has been critically examined as a method of assessing the wettability of five barbiturate powders. The contact angle was found to reduce with increased compression force, until a constant value was achieved. This was demonstrated, by use of scanning electron micrographs, to be due to plastic deformation of the powder surface. The values of θ obtained did not alter after electrostatic forces were discharged with an antistatic gun, and are thus not responsible for the hydrophobic nature of the loosely compressed beds. The effect of drop size, in the range 10 to 50 μl, and surface roughness were not large enough to be detected amongst the scatter of results. Small drops of water on the plane faces of large crystals formed a contact angle in close agreement with the plastic skin on the compacts. It is postulated that the crystal defects and heterogeneities are responsible for raising the value of θ in the uncompacted powders. © 1986.