| AVS 62nd International Symposium & Exhibition | |
| Surface Science | Wednesday Sessions |
| Session SS-WeM |
| Session: | Environmental Interfaces, Ambient Surfaces, In-Operando Studies and Adsorption on 2D Materials |
| Presenter: | Michael Makowski, University of California Irvine |
| Authors: | M. Makowski, University of California Irvine J.M. Langford, University of California Irvine D. Tobias, University of California Irvine J.C. Hemminger, University of California Irvine |
| Correspondent: | Click to Email |
The liquid/vapor interface of aqueous 1- and 2-propanol solutions for a broad range of concentrations was studied using a liquid-jet ambient pressure X-ray Photoelectron Spectroscopy system at the Advanced Light Source synchrotron in the Lawrence Berkeley National Laboratory. At low concentrations, 1-propanol displays a clear propensity to lie at the solution surface, evidenced by an enhanced carbon 1s XPS signal for electrons of low kinetic energy. Near a concentration (mole fraction) of 0.01 mf, a surface layer of 1-propanol appears to saturate, as evidenced by the saturation of the carbon 1s to oxygen 1s XPS signal ratio. Furthermore, over increasing concentrations carbon and oxygen 1s binding energies show a sharp redshift of 1 eV, until reaching a concentration of approximately 0.01 mf. This suggests an increasing 1-propanol density at the surface, with the resulting surface dipole layer causing a shift in the observed C1s and O1s binding energies for the condensed species.
These results of aqueous 1-propanol are compared and contrasted to similarly obtained aqueous 2-propanol carbon and oxygen spectra. Moreover, experimental results were corroborated with classical molecular dynamics simulations. Density profiles relative to an instantaneous interface were calculated for aqueous 1-propanol solutions. MD simulations indicate that 1-propanol accumulates at the surface at very low concentrations an a surface layer saturates at approximately 0.01 mf in agreement with the experimental results.