title: Probing the adsorption of weak acids on graphite using amplitude modulation-frequency modulation atomic force microscopy.
abstract: Recent thermodynamics calculations and adsorption isotherms showed that the adsorption of a self-assembled layer (SAL) of ionized weak acids to carbon was attributed to the negatively charged hydrogen bonding (-CAHB), yet the direct visualization and characterization of this adsorption behavior have not been reported. Here, an amplitude modulation-frequency modulation atomic force microscopy (AM-FM AFM) technique was applied to discriminate the adsorption of decanoic acids (DA) on highly ordered pyrolytic graphite (HOPG). Thermodynamics calculations revealed that the adsorption of SAL was driven by the formation of -CAHB with negatively charged functional groups of HOPG. Multilayer adsorption could occur over the adsorbed ionized SAL, leading to the development of aggregates. AM-FM AFM imaging showed that the adsorption of the DA molecules forming aggregates occurred only for the HOPG-functionalized steps, while DA molecules were found to adsorb over the entire functionalized HOPG surface after water-plasma treatment, as evident from the frequency shifts identified in AFM images.
authors.affiliation: †Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Ahmed M A
authors.initials: AM
authors.lastname: Moustafa
authors.affiliation: ‡Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Jun
authors.initials: J
authors.lastname: Huang
authors.affiliation: †Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Kerry N
authors.initials: KN
authors.lastname: McPhedran
authors.affiliation: ‡Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta T6G 2V4, Canada.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Zeng
authors.affiliation: †Department of Civil and Environmental Engineering, University of Alberta, Edmonton, Alberta T6G 2W2, Canada.
authors.forename: Mohamed Gamal
authors.initials: MG
authors.lastname: El-Din
mesh_terms: D000327:Adsorption; D003652:Decanoic Acids / Q000737:chemistry*; D006108:Graphite / Q000737:chemistry*; D055595:Mechanical Phenomena; D018625:Microscopy, Atomic Force; D013499:Surface Properties; D013816:Thermodynamics
chemical_list: D003652:Decanoic Acids; C031071:decanoic acid; D006108:Graphite