Assessment of the degree of disorder in crystalline solids by isothermal microcalorimetry

Abstract

The use of isothermal heat-conduction microcalorimetry for assessment of degree of the disorder within crystalline material has been evaluated. Single entities, physical mixtures with varying contents of 100% amorphous lactose and 100% crystalline α-lactose monohydrate, and samples of spray dried lactose with varying degrees of disorder were analysed at 25°C. The technique monitors the heat flow from the crystallisation of the amorphous content of the powder, when the powder is exposed to a humid environment. The heat calculated from the heat flow curve by integration revealed good linearity. The technique was able to detect at least 2% disorder in a crystalline sample. Comparisons with X-ray analysis and DSC showed good agreement above 10% disorder. At lower degrees of disorder only microcalorimetry was able to measure the disorder with high accuracy.