Crystal Habits and the Variation in Surface Energy Heterogeneity

The anisotropicity of crystal facets means that the overall adhesion property or wetting behavior of a crystalline batch is dependent on the crystal habits of the constituent particles. A recently developed method based on inverse gas chromatography at finite concentration was applied to study the variation in surface energy heterogeneity of the β form of d-mannitol exhibiting different crystal morphologies. The dispersive surface energy distributions were measured for d-mannitol crystals exhibiting various aspect ratios as confirmed by dynamic image analysis. d-Mannitol crystals with dissimilar crystal aspect ratios have a similar range of surface energies but are significantly different in the relative proportion of energy values. As the aspect ratio of d-mannitol decreased, there was a decreasing shift in the overall contribution of the lower dispersive surface energy regions, which was attributed to the decrease in the proportion of the lowest energy crystal facet. This study confirms that crystal shape has a profound influence on the overall surface heterogeneity.