title: Free energy calculations in electroactive self-assembled monolayers (SAMs): impact of the chain length on the redox reaction.
abstract: The free energy approach is used to study the effect of the relative chain length of the two constituents of electroactive self-assembled monolayers (SAMs) on gold. In this study, the ferrocene groups are exposed to the electrolyte solution. This situation is achieved by using shorter diluent alkanethiol chains. To this end, the mixed monolayers formed by the self-assembly of 11-ferrocenylundecanethiol and butanethiol FcC(11)S/C(4)S and of 6-ferrocenylhexanethiol and butanethiol FcC(6)S/C(4)S onto a gold surface are studied. Calculation of enthalpy and entropy differences are also performed using molecular simulations. Additionally, the electrochemical signatures of these systems are determined to allow a direct comparison with our calculations. The thermodynamic properties are discussed in terms of enthalpy and entropy changes. Two effects account for the thermodynamic behavior. The first one involves the ion pairing between the ferrocenium group and the perchlorate anion. The second one concerns the desolvation of the first hydration shell of the anions. Finally, this work is also completed with a microscopic description associated with an energy characterization of these SAMs as a function of the surface coverage under conditions close to experiments.
authors.affiliation: Laboratoire de Thermodynamique et Interactions Moléculaires, UMR CNRS 6272, Université Blaise Pascal, 63177 Aubière Cedex, France.
authors.forename: Gaelle
authors.initials: G
authors.lastname: Filippini
authors.forename: Yael
authors.initials: Y
authors.lastname: Israeli
authors.forename: Florent
authors.initials: F
authors.lastname: Goujon
authors.forename: Benoit
authors.initials: B
authors.lastname: Limoges
authors.forename: Christine
authors.initials: C
authors.lastname: Bonal
authors.forename: Patrice
authors.initials: P
authors.lastname: Malfreyt
mesh_terms: D055664:Electrochemical Techniques; D005296:Ferrous Compounds / Q000737:chemistry; D006046:Gold / Q000737:chemistry; D056004:Molecular Dynamics Simulation; D010084:Oxidation-Reduction; D013438:Sulfhydryl Compounds / Q000737:chemistry; D013499:Surface Properties; D013816:Thermodynamics; D053835:Unilamellar Liposomes / Q000737:chemistry*
chemical_list: D005296:Ferrous Compounds; D013438:Sulfhydryl Compounds; D053835:Unilamellar Liposomes; C064804:ferrocenium; D006046:Gold; C025540:n-butyl mercaptan