Impact of Particle Surface Properties and Molecular Dynamics on Powder Caking, Flow and Formulation Performance

Formulated products are often multicomponent, multiphase products whose performance properties depends on both the physical and chemical attributes across different length scales, ranging from the bulk to the surface molecular level. Due to the ease of handling and storage, formulated products are often manufactured into the form of bulk powders, however, over time these can exhibit caking behaviour resulting in negative financial implications for companies. Whilst the onset of caking and characterisation of caked powders can be measured using bulk techniques, the molecular level mechanism of caking in non-water soluble materials that exhibit complex solid-state behaviour in the presence of water remains poorly understood.

Near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) is a highly surface sensitive instrument that allows molecular level measurements under controlled environmental conditions replicating real world scenarios. This renders it possible to carry out in situ caking experiments whilst monitoring the dynamic molecular level interactions.

Here, the response of caking materials to elevated temperatures and humidity will be probed both ex situ and in situ using NAP-XPS alongside more conventional methods such as XRD, FTIR, DSC and DVS. From this, a powder caking mechanism will be proposed. This combined approach will highlight the usefulness of studying both the bulk and the surface properties to understand the interactions of a material both with its environment and within itself. It also represents an exciting new application of NAP-XPS which is not commonly used in this field.