Surface Characterization of Aspirin Crystal Planes by Dynamic Chemical Force Microscopy

摘要

Tapping mode (EM) atomic force microscopy (AFM) has been applied in a novel fashion to characterize and distinguish the (001) and (100) surfaces of individual aspirin crystals. The surface characterization was achieved by amplitude-phase, distance (a-p,d) measurements em-ploying gold-coated AFM probes functionalized with self~ assembled monolayers (SAM). Experiments using model probes coated with —CH3 and —COOH terminated SAMs have been performed on the two aspirin crystal planes (001) and (100). Results indicate that the hydrophobic—CHa terminated AFM probes had a greater degree of interac~ion with the crystal plane (001), whereas the —COOH terminated AFM probes had a larger interaction with the crystal plane (100). Interpretation of these data, based upon the chemistries of the probes, correlates with current understanding of the crystal surface chemistry derived from X-ray diffraction data and dissolution rate studies.