Surface Hydrophilicity-Dependent Water Adsorption on Mixed Self-Assembled Monolayers of C(7)-CH(3) and C(7)-COOH Residues. A Grand Canonical Monte Carlo Simulation Study

TitleSurface Hydrophilicity-Dependent Water Adsorption on Mixed Self-Assembled Monolayers of C(7)-CH(3) and C(7)-COOH Residues. A Grand Canonical Monte Carlo Simulation Study
Publication TypeJournal Article
Year of Publication2011
AuthorsSzori M, Roeselova M, Jedlovszky P
JournalJournal Of Physical Chemistry C
Volume115
Pagination19165-19177
Date PublishedOCT 6
ISSN1932-7447
Abstract

Grand Canonical Monte Carlo (GCMC) simulations are used to study the adsorption and organization of gas-phase water molecules on two-component self-assembled monolayers (SAMs) of eight-carbon alkanethiols bound to a flat virtual carrier, as the character of the SAM surface is changing from completely hydrophobic to completely hydrophilic by randomly replacing methyl-terminated (C(7)-CH(3)) alkanethiol chains with carboxylic acid-terminated (C(7)-COOH) chains. At low chemical potentials (low relative humidity), a synergistic effect of nearby COOH functional groups on water adsorption is observed. In particular, clusters of nearby surface COOH groups are found to attract considerably more water molecule s than the same amount of COOH groups if they are isolated from each other. By promoting lateral water water interactions, such surface COOH clusters thus act as condensation nuclei for water. With increasing water chemical potential, the possibility of the formation of new water water hydrogen bonds gradually becomes an increasingly important driving force of the adsorption, in addition to the formation of new water-COOH hydrogen bonds. Further, as the relative humidity increases, the growing number of water water hydrogen bonds clearly overcompensates the effect of the decreasing average number of water-COOH hydrogen bonds per (first layer) water molecules. These findings are supported by the adsorption isotherms, by the preferential orientation of the surface COOH groups and first layer water molecules, and by the binding energy distributions of the water molecules being in direct contact with the SAM surface as obtained from the simulation. The atmospheric relevance of our results is also considered.

DOI10.1021/jp201224h