Analysis of powder caking in multicomponent powders using atomic force microscopy to examine particle properties

Atomic force microscopy has been used to study the surface properties of model spray dried powders. Phase imaging, nanoindentation and force modulation microscopy have differentiated between the different surface material properties of the particles, revealing a regular dispersion of soft, oil rich areas distributed across the particles' surface. Humidity and temperature cycling effects on the caking behavior of the particles have also been investigated, with significant morphology changes and onset of caking found to occur within relatively short periods of time.

The use of atomic force microscopy in investigating particle caking mechanisms

Spray-dried materials are being used increasingly in industries such as food, detergent and pharmaceutical manufacture. Spray-dried sodium carbonate is an important product that has a great propensity to cake; its moisture-sorption properties are very different to the crystalline and amorphous species, with a great affinity for atmospheric moisture. This work demonstrates how the noncontact surface analysis of individual particles using atomic force microscopy can highlight the possible mechanisms of unwanted agglomeration. The nondestructive nature of this method allows cycling of localised humidity in situ and repeated scanning of the same particle area. The resulting topography and phase scans showed that humidity cycling caused changes in the distribution of material phases that were not solely dependent on topographical changes. © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.