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.

Activity and Reactivity of Pyrogenic Carbonaceous Matter toward Organic Compounds

“…103,104 Complexes between decanoic acid and −OH and −CO 2 H groups on functionalized highly ordered pyrolytic graphite that appear to form the CAHB have recently been imaged by atomic force microscopy. 104 The observed sorption obviously has contributions from hydrophobic effects, van der Waals, and specific interactions that may otherwise take place. 103 Ionizable compounds make up a large percentage of industrial pollutants, pesticides, personal care products, surfactants, pharmaceuticals, polyfluorinated compounds, and other compounds of emerging interest.…”

“…By contrast, the CAHB has considerable covalent character ,,, and can be upward of 37 kJ/mol. Reactions and have been shown to contribute to adsorption of weak acids ranging in p K a from 4 to 7, including aliphatic and aromatic carboxylic acids, phenols, aryl sulfonamides, and heterocyclic amines, on chars, , partially oxidized CNTs, ,, and functionalized graphite. , Complexes between decanoic acid and −OH and −CO 2 H groups on functionalized highly ordered pyrolytic graphite that appear to form the CAHB have recently been imaged by atomic force microscopy . The observed sorption obviously has contributions from hydrophobic effects, van der Waals, and specific interactions that may otherwise take place .…”

Bimodal AFM-Based Nanocharacterization of Cycling-Induced Topographic and Mechanical Evolutions of LiMn2O4 Cathode Films

“…Scanning probe microscopy (SPM), as a powerful characterization tool, has been successfully used to probe the surface topography, local mechanical property, and conductivity of the electrode materials at the nanoscale. − Among them, bimodal atomic force microscopy (AFM) (amplitude modulation–frequency modulation, AM–FM) is a particular technique that is capable of mapping the surface topography and mechanical property of the materials simultaneously . Compared with nanoindentation, the significant advantage of the bimodal AFM is nondestructive measurement due to small forces of magnitude in the order of nano-Newtons between the tip and the surface, providing an opportunity to study the evolution of the materials in their native environment and state.…”

“…16−21 Among them, bimodal atomic force microscopy (AFM) (amplitude modulation−frequency modulation, AM−FM) is a particular technique that is capable of mapping the surface topography and mechanical property of the materials simultaneously. 22 Compared with nanoindentation, the significant advantage of the bimodal AFM is nondestructive measurement due to small forces of magnitude in the order of nano-Newtons between the tip and the surface, providing an opportunity to study the evolution of the materials in their native environment and state. Moreover, the bimodal AFM guarantees the constant sensitivity across the material surface even if the surface is inhomogeneous and more quantitative data is sought.…”

Nanometer-Scale Distribution of a Lubricant Modifier on Iron Films: A Frequency-Modulation Atomic Force Microscopy Study Combined with a Friction Test

“…Hirayama et al 13 extended their method to include a hexadecane-based model lubricant that is more viscous than water. Moustafa et al 29 conducted a bimodal AFM study to visualize the lateral distribution of weakly adsorbed organic aggregates over graphite surfaces. A recent mapping study on a liquid ester lubricant with no modifier 30 reported the deposition of soft layers on a diamondlike carbon film following rubbing in a friction test, which was most likely a result of the tribochemical reactions of the lubricant.…”