D₂O Water Interaction with Mixed Alkane Thiol Monolayers of Tuned Hydrophobic and Hydrophilic Character

Abstract

We have used temperature-programmed desorption (TPD) experiments to characterize the interaction between D 2 O water and a self-assembled monolayer (SAM) of mixed hydrophobic and hydrophilic thiols on Au(111). Two-component SAM surfaces with tuned hydrophobic and hydrophilic character have been formed by exposing gold samples to solutions of octanethiol and 6-mercaptohexanoic acid in varying millimolar concentrations. Water desorption spectra from the pure hydrophobic surface exhibit first-order desorption at low coverage with the onset of zero-order character at ∼1 Langmuir with narrow peaks at ∼145 K. In contrast, desorption of D 2 O water from the pure carboxylic acid-terminated surface exhibits broad peaks shifted to higher temperatures. Interestingly, water TPD spectra from a 50% octanethiol/50% 6-mercaptohexanoic acid surface closely resemble desorption from the purely hydrophobic octanethiol SAM. Increasing the surface acid fraction beyond 50% shifts the TPD profiles to higher temperatures with long, high-temperature tails that approach the behavior of water desorbing from the hydrophilic 6-mercaptohexanoic acid surface. We discuss the implications for water interaction with "textured" organic surfaces as well as with atmospherically relevant organic aerosol particles. In particular, the results suggest that significant surface oxidation is necessary to impact the interaction of water with organic aerosol surfaces.

Reaction of gas phase OH with unsaturated self-assembled monolayers and relevance to atmospheric organic oxidations

“…This is similar to our previous results 51,68 where oxidation of the film using O 3 or KMnO 4 only slightly enhanced the uptake of water. Possible reasons for this are hydrogen-bonding between polar groups on the surface so they are not available for interaction with water 51,[69][70][71] or the polar groups being buried inside the organic surface film in such a way that they are not available for interaction with the gas phase. 72 …”

Spectroscopic Study of Water Adsorption and Desorption on/from Oligo(ethylene glycol)-Substituted Alkanethiolate Self-Assembled Monolayers

“…On the side of experiment, a variety of different tools are used, including surface force apparatus, , optical methods (infrared and Raman spectroscopy, ellipsometry, etc. ), − classical methods of surface science such as temperature-programmed desorption (TPD), and so forth, − X-ray scattering, ,, neutron scattering, X-ray spectroscopy, − and so forth. As far as well-defined organic or biology-relevant surface is required, it is frequently mimicked by molecular self-assembly on a solid support.…”

Water adsorption on hydrophilic and hydrophobic self-assembled monolayers as proxies for atmospheric surfaces. A grand canonical Monte Carlo simulation study

“…18 In particular, SAMs have been extensively used in experimental research on water adsorption and wetting of organic surfaces. [19][20][21][22] SAMs are excellent model systems for studying the interactions between water and organic surfaces as they give us a chance to investigate the properties of water in direct contact with an interface whose microscopic structure is well characterized and whose hydrophilic/hydrophobic character can be controlled. However, despite numerous studies motivated by its scientific importance and technological implications, the interaction of water with surfaces covered by SAMs is far from being fully understood.…”