The aim of this work was to assess the effect of different crystalline polymorphism on surface energetics of D-mannitol using finite dilution inverse gas chromatography (FD-IGC). Pure α, β and δ polymorphs were prepared via solution crystallisation and characterised by powder X-ray diffraction (P-XRD). The dispersive surface energies were found to range from 43 to 34 mJ/m2, 50 to 41 mJ/m2, and 48 to 38 mJ/m2, for α, β, and δ, respectively, for surface coverage ranging from 0.006 to 0.095. A deconvolution modelling approach was employed to establish their energy sites. The primary sites corresponded to maxima in the dispersive surface energy of 37.1 and 33.5; 43.3 and 39.5; and 38.6, 38.4 and 33.0; for α, β, and δ, respectively. This methodology was also extended to an α-β polymorph mixture to estimate the amount of the constituent α and β components present in the sample. The dispersive surface energies of the α-β mixture were found to be in the range of 48 to 37 mJ/m2 with 40.0, 42.4, 38.4 and 33.1 mJ/m2 sites. The deconvolution modelling method extracted the energy contribution of each of the polymorphs from data for the polymorphic mixture. The mixture was found to have a β-polymorph surface content of ∼19%. This work shows the influence of polymorphism on surface energetics and demonstrates that FD-IGC coupled with a simple modelling approach to be a powerful tool for assessing the specific nature of this energetic distribution including the quantification of polymorphic content on the surface.
D-mannitol inverse gas chromatography modelling polymorphism powder X-ray diffraction surface energy heterogeneity
This is a preview of subscription content, log in to check access.
The PhD studentship, supported by the Engineering and Physical Science Research Council and Surface Measurement Systems for Robert Smith, is gratefully acknowledged.
Fowkes FM. Dispersion force contributions to surface and interfacial tensions, contact angles, and heats of immersion. Contact Angle, Wettability, and Adhesion. Advances in Chemistry. 43: American Chemical Society, 1964. p. 99–111.Google Scholar