Advanced

Alcohols at the aqueous surface : Chain length and isomer effects

Walz, M. M.; Werner, J.; Ekholm, V.; Prisle, N. L.; Öhrwall, G. LU and Björneholm, O. LU (2016) In Physical Chemistry Chemical Physics 18(9). p.6648-6656
Abstract

Surface-active organic molecules at the liquid-vapor interface are of great importance in atmospheric science. Therefore, we studied the surface behavior of alcohol isomers with different chain lengths (C4-C6) in aqueous solution with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. Gibbs free energies of adsorption and surface concentrations are determined from the XPS results using a standard Langmuir adsorption isotherm model. The free energies of adsorption, ranging from around -15 to -19 kJ mol-1 (C4-C6), scale linearly with the number of carbon atoms within the alcohols with ΔGAds per -CH2- ≈ -2 kJ... (More)

Surface-active organic molecules at the liquid-vapor interface are of great importance in atmospheric science. Therefore, we studied the surface behavior of alcohol isomers with different chain lengths (C4-C6) in aqueous solution with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. Gibbs free energies of adsorption and surface concentrations are determined from the XPS results using a standard Langmuir adsorption isotherm model. The free energies of adsorption, ranging from around -15 to -19 kJ mol-1 (C4-C6), scale linearly with the number of carbon atoms within the alcohols with ΔGAds per -CH2- ≈ -2 kJ mol-1. While for the linear alcohols, surface concentrations lie around 2.4 × 1014 molecules per cm2 at the bulk concentrations where monolayers are formed, the studied branched alcohols show lower surface concentrations of around 1.6 × 1014 molecules per cm2, both of which are in line with the molecular structure and their orientation at the interface. Interestingly, we find that there is a maximum in the surface enrichment factor for linear alcohols at low concentrations, which is not observed for the shorter branched alcohols. This is interpreted in terms of a cooperative effect, which we suggest to be the result of more effective van der Waals interactions between the linear alcohol alkyl chains at the aqueous surface, making it energetically even more favorable to reside at the liquid-vapor interface.

(Less)
Please use this url to cite or link to this publication:
author
organization
publishing date
type
Contribution to journal
publication status
published
subject
in
Physical Chemistry Chemical Physics
volume
18
issue
9
pages
9 pages
publisher
The Royal Society of Chemistry
external identifiers
  • Scopus:84959155571
ISSN
1463-9076
DOI
10.1039/c5cp06463e
language
English
LU publication?
yes
id
0c968baa-f4aa-4339-ac34-29cb158575f6
date added to LUP
2016-09-21 14:14:34
date last changed
2016-09-22 03:00:02
@misc{0c968baa-f4aa-4339-ac34-29cb158575f6,
  abstract     = {<p>Surface-active organic molecules at the liquid-vapor interface are of great importance in atmospheric science. Therefore, we studied the surface behavior of alcohol isomers with different chain lengths (C4-C6) in aqueous solution with surface- and chemically sensitive X-ray photoelectron spectroscopy (XPS), which reveals information about the surface structure on a molecular level. Gibbs free energies of adsorption and surface concentrations are determined from the XPS results using a standard Langmuir adsorption isotherm model. The free energies of adsorption, ranging from around -15 to -19 kJ mol<sup>-1</sup> (C4-C6), scale linearly with the number of carbon atoms within the alcohols with ΔG<sub>Ads</sub> per -CH<sub>2</sub>- ≈ -2 kJ mol<sup>-1</sup>. While for the linear alcohols, surface concentrations lie around 2.4 × 10<sup>14</sup> molecules per cm<sup>2</sup> at the bulk concentrations where monolayers are formed, the studied branched alcohols show lower surface concentrations of around 1.6 × 10<sup>14</sup> molecules per cm<sup>2</sup>, both of which are in line with the molecular structure and their orientation at the interface. Interestingly, we find that there is a maximum in the surface enrichment factor for linear alcohols at low concentrations, which is not observed for the shorter branched alcohols. This is interpreted in terms of a cooperative effect, which we suggest to be the result of more effective van der Waals interactions between the linear alcohol alkyl chains at the aqueous surface, making it energetically even more favorable to reside at the liquid-vapor interface.</p>},
  author       = {Walz, M. M. and Werner, J. and Ekholm, V. and Prisle, N. L. and Öhrwall, G. and Björneholm, O.},
  issn         = {1463-9076},
  language     = {eng},
  number       = {9},
  pages        = {6648--6656},
  publisher    = {ARRAY(0x8710098)},
  series       = {Physical Chemistry Chemical Physics},
  title        = {Alcohols at the aqueous surface : Chain length and isomer effects},
  url          = {http://dx.doi.org/10.1039/c5cp06463e},
  volume       = {18},
  year         = {2016},
}