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Nanoscale Imaging of Molecular Adsorption
Technical rept. no. 4, 1 May 1993-30 Jun 1994
MINNESOTA UNIV MINNEAPOLIS DEPT OF CHEMICAL ENGINEERING AND MATERIALS SCIENCE
Pagination or Media Count:
The adsorption of organic molecular species onto highly ordered, chemically well defined substrates may provide insights into the intermolecular interactions, molecular recognition, and aggregation phenomena responsible for the formation of organic thin film and solid state assemblies. The advent of scanning probe microscopy, particularly the atomic force microscope, now provides a method for observation of these adsorption processes on the molecular level. We herein report atomic force microscope observations of the adsorption of anions of the organic di-acid 5-benzoyl-4-hydroxy-2-methoxybenzenesulfonic acid from aqueous solution onto the 0001 surface of hydrotalcite, a layered anionic clay. This adsorption process is believed to mimic the ion exchange reactions that commonly occur within the layers of hydrotalcite. Atomic force microscope images reveal that the coverage of the adsorbed anions depends upon the total charge of the anion 1- or 2-. This is due to electroneutrality requirements associated with coulombic interactions between the cationic hydrotalcite surface and the anionic molecules. The AFM data, along with consideration of coulombic interactions and hydrogen bonding between three-fold clay hydroxyl sites and the sulfonate moiety on the anions, enables tentative assignment of the orientation of the anions with respect to the hydrotalcite surface. Organic conductors, Atomic force microscopy, Nucleation, Fractals.
APPROVED FOR PUBLIC RELEASE