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Title: Adsorption, Ordering, and Local Environments of Surfactant-Encapsulated Polyoxometalate Ions Probed at the Air–Water Interface

The continued development and application of surfactant-encapsulated polyoxometalates (SEPs) relies on understanding the ordering and organization of species at their interface and how these are impacted by the various local environments to which they are exposed. In this paper, we report on the equilibrium properties of two common SEPs adsorbed to the air–water interface and probed with surface-specific vibrational sum-frequency generation (SFG) spectroscopy. These results reveal clear shifts in vibrational band positions, the magnitude of which scales with the charge of the SEP core, which is indicative of a static field effect on the surfactant coating and the associated local chemical environment. This static field also induces ordering in surrounding water molecules that is mediated by charge screening via the surface-bound surfactants. From these SFG measurements, we are able to show that Mo132-based SEPs are more polar than Mo72V30 SEPs. Disorder in the surfactant chain packing at the highly curved SEP surfaces is attributed to large conic volumes that can be sampled without interactions with neighboring chains. Measurements of adsorption isotherms yield free energies of adsorption to the air–water interface of -46.8 ± 0.4 and -44.8 ± 1.2 kJ/mol for the Mo132 and Mo72V30 SEPs, respectively, indicating a strong propensitymore » for the fluid surface. Finally, the influence of intermolecular interactions on the surface adsorption energies is discussed.« less
Authors:
 [1] ;  [2] ;  [1]
  1. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical Sciences Division
  2. Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States). Chemical and Engineering Materials Division and Shull Wollan Center, Neutron Sciences Directorate
Publication Date:
OSTI Identifier:
1324104
Grant/Contract Number:
AC05-00OR22725
Type:
Accepted Manuscript
Journal Name:
Langmuir
Additional Journal Information:
Journal Volume: 32; Journal Issue: 32; Journal ID: ISSN 0743-7463
Publisher:
American Chemical Society
Research Org:
Oak Ridge National Laboratory (ORNL), Oak Ridge, TN (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY polyoxometalate; trioctylmethylammonium; SEP surfactant encapsulated polyoxometalate; Sum-frequency generation; symmetric stretch; asymmetric stretch