(211a) Adhesion Force Prediction for Surface Modified Fine Particles From Surface Energy and Surface Roughness Measurements

Fine powder flow is a topic of great interest to industry, in particular for the pharmaceutical and energetic materials industry; a major concern being their poor flow behavior due to high cohesion. We present results for various fine powders, where cohesion reduction is achieved via surface modification. Results of the bulk properties for these powders are presented to illustrate the improvement in flow and fluidization. The adhesion force model of Derjaguin-Muller-Toporov (DMT) is utilized to quantify the inter-particle adhesion force of both original and surface modified powders. Inverse Gas Chromatography (IGC) is utilized for the determination of surface energy of the samples, and Atomic Force Microscopy (AFM) is utilized to evaluate surface roughness of the powders. For selected samples, the AFM is utilized for direct evaluation of the particle pull-off force. The results indicate that surface modification reduced the surface energy and altered the surface nano-roughness, resulting in drastic reduction of the inter-particle adhesion force. Surface modification resulted in two to three fold reductions in the particle Bond number. In order to examine the influence of the particle scale property such as the Bond number with the bulk-scale flow characterization, Flow Function Coefficient (FFC), Angle of Repose (AOR), and electrostatic and dielectric properties measurements are done to examine if there are good correlations between them. Preliminary results indicate good correlation between the bulk-scale flow measurements and particle scale prediction using the proposed methodology, which indicate a promising method that may be used to predict flow behavior of cohesive and surface modified powders utilizing very small samples. Moreover, the surface modification can drastically improve the powder flow for industrially relevant materials.