Assessment of the wettability and surface energy of a pharmaceutical powder by liquid penetration.

The use of a technique involving the assessment of the rate of penetration of a liquid into powder beds has been critically evaluated as a method for characterizing the wetting and surface energy of a hydrophobic powder (amylobarbitone). The choice of the perfect wetting liquid has been assessed, and the possible use and value of extrapolation techniques to indicate the theoretical result for water have been explored. Values of 99.5 and 102.8 obtained for the contact angle, and 25.7 and 26.9 mNm-1 for the critical surface energy, were the best estimates obtainable by this technique. Previously reported limitations of the Washburn equation have been considered.