Monday, November 8, 2010
Hall 1 (Salt Palace Convention Center)
Powder processing is plagued by issues of caking and sticking which contribute to the inability to predict the behavior of powders. This leads to unusable products and an increase in unnecessary waste. In this study, new techniques are used and developed to study the effect of capillary condensation under humid conditions using atomic force microscopy (AFM) with α-lactose monohydrate (ALM) as the model powder, one of the most common pharmaceutical excipient in formulation. Phase imaging was used to measure the change in surface moisture on stainless steel and Perspex® as relative humidity was increased by 10% increments between 15 and 65%. For hydrophilic stainless steel, the low energy (high moisture) regions correlated closely with the topology of the surface roughness. Liquid accumulated in the valleys as RH levels increased and reversible adhesion force profile between silicon nitride and stainless steel increased from 3 nN to 30 nN due to capillary bridging. For silicon nitride and Perspex, no significant effects of RH on condensation or the adhesion force which was maintained at ~25 nN; an expected value and behavior for a hydrophobic surface such as Perspex. Results for adhesion forces of mounted ALM particles and the surfaces were more difficult to interpret. The force measurements for ALM against each of the surfaces showed a hysteresis or irreversible adhesion force profiles as RH was increased and then decreased. It was observed that the hysteresis was due to ALM surface reacting with condensed moisture by dissolving small features on the surface. Although, visual observation of the morphological changes of the particles coupled with adhesion force profiles is informative, there a need to develop other methodologies so the capillary condensation can be studied with ALM particles independent of any morphological changes.