FM-AFM Observation of Competitive Adsorption on Graphite Takumi Hiasa and Hiroshi Onishi
Department of Chemistry, Graduate School of Science, Kobe University In this study…

Competitive Adsorption at Solid-Liquid Interface
Solute adsorption from a solution is akey process in many phenomena suchas crystal growth. When a solution faces
to a solid surface, solute and solvent
molecules competitively adsorbed on thesurface. Interfacial liquids play a key role in adsorption process. Direct observation of interfacial liquid structure can be aneffective approach for understanding adsorption process.

          Instrument

Using an advanced FM-AFM, interfacial structuresof long-chain organic compounds were visualizedwith sub-nanometer resolution over the graphite
surface.
We focused on the interface where two components
competitively adsorbed.

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Dilute Decanol Solution of Carboxylic Acids

Our AFM is Shimadzu WETSPM 9600 modified with a low
noise optical deflection
sensing system* allowing
highly-sensitive force
detection also in solutions.

Stearic Acid (C17H35COOH: 10 mM)
f distribution perpendicular to the lamellae axis

Topography*T. Fukuma et al., Appl. Phys. Lett. 86 (2005) 193108. Cross-sectional f distribution

Decanol adlayer
Lignoceric Acid (C23H47COOH: 0.5 mM)With precise measurement of the interaction force toward the tip as a function of the tip
coordination, small force modulation appears which may be related with the sitespecific density of liquid molecules.
K. Kimura et al.: J. Chem. Phys. 132 (2010) 194705.

 T. Hiasa et al.: J. Phys. Chem. C 114 (2010) 21423.

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Decanol adlayer

Topography of Decanol Adlayer on GraphiteWide-area

Narrow-area

Model

Adlayers composed exclusively of the solvent decanol were found for the diluted solutions.
Interfacial liquid structures were totally same as of pure decanol.
(There was no sign of contribution by the solute stearic acid, or lignoceric acid.)

SaturatedCondition

Saturated Decanol Solution of Carboxylic Acids
Saturated Stearic Acid (200 mM)S. Yin et al.
Chem. Phys. Lett. 348 (2001) 321.

Topography

f distribution perpendicular to the lamellae axis

Molecular layer of decanol was developed on graphite surface.
Dimerized OH groups appeared as bright spots at the center of the lamellae.

Interfacial Structure of Decanol Liquids
(1) Perpendicular to the lamellae axis

Direction ofcross-sectional distribution

Stearic acid adlayer
Saturated Lignoceric Acid (9 mM)Topography(2) Nearly parallel to the lamellae axis

Liquid structure was epitaxial tothe adsorbed layer.
Density was enhanced on top of theadsorbed molecules.

T. Hiasa et al.: J. Phys. Chem. C 116 (2012) 26475.

Energy gain of van der Waals andhydrogen bond interactions were
maximized on top of them.

Lignoceric acid adlayer
Adlayers of the solute carboxylic acids were formed in the saturated solution.
Liquid structure at the interface was controlled by the solute concentration via thecomposition of adsorbed materials. 

Saturated condition is a key in selective adsorption of the solute carboxylic
acid and solvent decanol, not dependent to absolute concentration.
Interfacial liquids are structured epitaxial to the adlayer.
T. Hiasa and H. Onishi submitted.