Nonuniform friction-area dependency for antimony oxide surfaces sliding on graphite

Cataloged from PDF version of article.We present frictional measurements involving controlled lateral manipulation of antimony nanoparticles on graphite featuring atomically smooth particle-substrate interfaces via tapping- and contact-mode atomic force microscopy. As expected from earlier studies, the power required for lateral manipulation as well as the frictional forces recorded during the manipulation events exhibit a linear dependence on the contact area over a wide size range from 2000 nm2 to 120 000 nm2. However, we observe a significant and abrupt increase in frictional force and dissipated power per contact area at a value of about 20 000 nm2, coinciding with a phase transition from amorphous to crystalline within the antimony particles. Our results suggest that variations in the structural arrangement and stoichiometry of antimony oxide at the interface between the particles and the substrate may be responsible for the observed effect. © 2013 American Physical Society

Supply and Demand in the Ball Mill Competitive Cocrystal Reactions

The stability of different theophylline cocrystals under milling conditions was investigated by competitive cocrystal reactions. To determine the most stable cocrystal form under milling conditions, the active pharmaceutical ingredient theophylline was either ground with two similar coformers (benzoic acid, benzamide, or isonicotinamide), or the existing theophylline cocrystals were ground together with a competitive coformer. All competitive reactions were investigated by in situ powder X-ray diffraction disclosing the formation pathway of the milling processes. On the basis of these milling reactions, a stability order (least to most stable) was derived: tp/bs < tp/ba < tp/ina < bs/ina