Wetting Behavior of Ibuprofen Racemate Surfaces

Abstract The wetting behavior and detailed surface energetics of a racemate crystalline system were measured via contact angle measurements and inverse gas chromatography at finite concentrations. The advancing contact angles for water, diiodomethane, formamide, and ethylene glycol were measured on specific facets for racemic ibuprofen and S-(+)-ibuprofen single macroscopic crystals, and were found to be facet dependent for both systems. This observation demonstrates that variation in molecular orientation within the crystal lattice results in variations in exposed surface chemistry for differing facets, which results in anisotropic wetting behavior as previously reported. Surface free energy profiles of the ibuprofen racemates determined using a novel inverse gas chromatography method showed that powder samples (75–150 µm particle diameter) exhibited relatively homogeneous surface energies, with similar values of γSV d to those obtained by the contact angle analysis. These results lead us to conclude that ibuprofen exhibited a low level of surface heterogeneity, with the dominant facet of these powders exhibiting a low γSV d, with high energetic sites estimated to be < 3% of exposed available surface. Keywords: Contact angleCrystalsHeterogeneityInverse gas chromatographyOptical isomersSurface chemistrySurface free energyWetting ACKNOWLEDGMENTS The authors would like to acknowledge the use of the Engineering and Physical Sciences Research Council's. Chemical Database Service at Daresbury and R.H. would also like to acknowledge the financial support of AstraZeneca UK. Notes One of a Collection of papers honouring John F. Watts, the receipient in February 2008 of The Adhesion Society Award for Excellence in Adhesion Science, Sponsored by 3M.