The use of inverse phase gas chromatography to measure the surface energy of crystalline, amorphous, and recently milled lactose

Purpose. To assess differences in surface energy due to processing induced disorder and to understand whether the disorder dominated the surfaces of p articles. Methods. Inverse gas chromatography was used to compare the surface energie s of crystalline, amorphous, and ball milled lactose. Results. The milling process made ca 1% of the lactose amorphous, however t he dispersive contribution to surface energy was 31.2, 37.1, and 41.6 mJ m( -2) for crystalline, spray dried and milled lactose. respectively. A physic al mixture of crystalline (99%) and amorphous (1%) material had a dispersiv e surface energy of 31.5 mJ m(-2) Conclusion. Milling had made the surface energy similar to that of the amor phous material in a manner that was very different to a physical mixture of the same amorphous content. The milled material will have similar interfac ial interactions to the 100% amorphous material.