Publication type: Article in scientific journal
Type of review: Peer review (publication)
Title: Solvent dependence of the activation energy of attachment determined by single molecule observations of surfactant adsorption
Authors : Honciuc, Andrei
Baptiste, Denver Jn.
Campbell, Ian P.
Schwartz, Daniel K.
DOI : 10.1021/la900307f
Published in : Langmuir
Volume(Issue) : 25
Issue : 13
Pages : 7389
Pages to: 7392
Issue Date: 2009
Publisher / Ed. Institution : American Chemical Society
ISSN: 0743-7463
Language : English
Subject (DDC) : 540: Chemistry
Abstract: Single-molecule total internal reflection fluorescence microscopy was used to obtain real-time images of fluorescently labeled hexadecanoic (palmitic) acid molecules as they adsorbed at the interface between fused silica and three different solvents: hexadecane (HD), tetrahydrofuran (THF), and water. These solvents were chosen to explore the effect of solvent polarity on the activation energy associated with the attachment rate, i.e., the rate at which molecules were transferred to the surface from the near-surface layer. Direct counting of single-molecule events, made under steady-state conditions at extremely low coverage, provided direct, model-independent measurements of this attachment rate, in contrast with conventional ensemble-averaged methods, which are influenced by bulk transport and competing detachment processes. We found that the attachment rate increased with increasing temperature for all solvents. Arrhenius analyses gave activation energies of 5+/-2 kJ/mol for adsorption from HD, 10+/-2 kJ/mol for adsorption from THF, and 19+/-2 kJ/mol for adsorption from water. These energies increased systematically with the solvent polarity and, therefore, with the expected strength of the solvent-substrate interaction. We hypothesize that the adsorption of amphiphilic solute molecules from solution can be regarded as a competitive exchange between solute molecules and surface-bound solvent. In this scenario, adsorption is an activated process, and the activation energy for attachment is associated with the solvent-substrate interaction energy.
Fulltext version : Published version
License (according to publishing contract) : Licence according to publishing contract
Departement: Life Sciences and Facility Management
Organisational Unit: Institute of Chemistry and Biotechnology (ICBT)
Appears in Collections:Publikationen Life Sciences und Facility Management

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