Surface Free Energy
Measurements of surface free energy are gaining popularity due to the availability of automated equipment. MPS has two different analytical techniques available for surface free energy measurement, Inverse Gas Chromatography (IGC) and Volumetric Gas Sorption.
The surface free energy of solids is influenced by particle morphology and surface contamination. The choice of crystallization solvent may affect the relative area of each crystal plane. Because each crystal has a different surface free energy, the average surface free energy is changed by the crystallization process. Milling also affects the area of the exposed crystal planes. Some materials (e.g. lactose) may be contaminated with a submonolayer of other materials in the mother liquor (milk components in the case of lactose) that are not readily detected by standard chemical analysis.
Monitoring surface free energy can assure consistent product performance. Surface free energy is a major factor influencing the adhesion between particles. Changes in surface free energy are known to affect the dispersion of powders used in dry powder inhalation formulations. Surface free energy and the adhesion between particles also influence the flow of fine powders and the tensile strength of tablets. The wettability and penetration of liquids into powders depends upon the surface free energy.