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A vibrational sum frequency spectroscopy study of the liquid-gas interface of acetic acid-water mixtures: 1: surface speciation
KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.ORCID-id: 0000-0002-8935-8070
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2005 (Engelska)Ingår i: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 109, nr 1, s. 321-328Artikel i tidskrift (Refereegranskat) Published
Abstract [en]

Aqueous acetic acid solutions have been studied by vibrational sum frequency spectroscopy (VSFS) in order to acquire molecular information about the liquid-gas interface. The concentration range 0-100% acetic acid has been studied in the CH/OH and the C-O/C=O regions, and in order to clarify peak assignments, experiments with deuterated acetic acid and water have also been performed. Throughout the whole concentration range, the acetic acid is proven to be protonated. It is explicitly shown that the structure of a water surface becomes disrupted even at small additions of acetic acid. Furthermore, the spectral evolution upon increasing the concentration of acetic acid is explained in terms of the different complexes of acetic acid molecules, such as the hydrated monomer, linear dimer, and cyclic dimer. In the C=O region, the hydrated monomer is concluded to give rise to the sum frequency (SF) signal, and in the CH region, the cyclic dimer contributes to the signal as well. The combination of results from the CH/OH and the C-O/C=O regions allows a thorough characterization of the behavior of the acetic acid molecules at the interface to be obtained.

Ort, förlag, år, upplaga, sidor
2005. Vol. 109, nr 1, s. 321-328
Nyckelord [en]
CH3COOH CH3COOD CD3COOH; AQUEOUS-SOLUTIONS; RAMAN-SPECTRA; AIR/WATER INTERFACE; CARBOXYLIC-ACIDS; IR-SPECTRA; AB-INITIO; GENERATION; MOLECULES; CORROSION
Nationell ämneskategori
Kemi
Identifikatorer
URN: urn:nbn:se:kth:diva-7699DOI: 10.1021/jp047338qISI: 000226213200048Scopus ID: 2-s2.0-12344332758OAI: oai:DiVA.org:kth-7699DiVA, id: diva2:12803
Anmärkning
QC 20100825Tillgänglig från: 2005-10-20 Skapad: 2005-10-20 Senast uppdaterad: 2017-12-14Bibliografiskt granskad
Ingår i avhandling
1. Vibrational Sum Frequency and Infrared Reflection/Absorption Spectroscopy Studies of the Air/Liquid and Liquid/Metal Interfaces
Öppna denna publikation i ny flik eller fönster >>Vibrational Sum Frequency and Infrared Reflection/Absorption Spectroscopy Studies of the Air/Liquid and Liquid/Metal Interfaces
2005 (Engelska)Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
Abstract [en]

Atmospheric corrosion, the most common form of metal corrosion, occurs within the interfacial region between a solid, and the surrounding atmosphere. In fact three phases and two interfaces are involved: the gas, a thin liquid layer, a solid, the gas/liquid and the liquid/solid interfaces. In this thesis, the vapor/liquid and liquid/metal interfaces have been studied by the in-situ techniques vibrational sum frequency spectroscopy (VSFS), and infrared reflection/absorption spectroscopy (IRAS). The main focus has been on characterization of the corrosive organic molecules formic acid, acetic acid, and acetaldehyde, at the two interfaces. Additionally, the headgroup of sodium dodecyl sulfate (SDS) has been examined at the air/water interface.

VSFS is an inherently surface sensitive laser spectroscopy technique, which provides vibrational spectra solely of the molecules residing at the surface of for example a liquid, despite the vast excess of the same molecules in the bulk. To obtain a comprehensive molecular picture of the organic compounds at the air/liquid interface, studies have been undertaken in several spectral regions, targeting the CH, C=O, C-O, OH, and SO3 stretching vibrations. Furthermore, the surrounding water molecules have been investigated in order to study hydration phenomena. Acetaldehyde has been determined to partly form a gem-diol (CH3CH(OH)2) at the air/water interface, whereas acetic acid forms various hydrogen-bonded species, with hydrated monomers at low concentrations and centrosymmetric cyclic dimers at high concentrations. Formic acid was found to form a different complex at very high concentrations, in addition to the species observed at low concentrations. Performing experiments with different polarizations of the laser beams has enabled the determination of the orientation of the interfacial molecules. The methyl group of acetic acid was concluded to be oriented close to the surface normal throughout the concentration range, whereas the tilt angle of the CH group of formic acid was determined to be ~35°. The SDS studies revealed that the headgroup orientation is constant in a wide range of concentrations, and also in the presence of sodium chloride.

IRAS has provided information regarding the composition and kinetics of the corrosion products formed upon exposure of a zinc oxide surface to the organic compounds. The importance of the water adlayer on metal surfaces has been confirmed by the faster kinetics observed at higher relative humidities. Exposure to formic acid resulted in the formation of zinc formate, whereas both acetic acid and acetaldehyde formed zinc acetate upon reaction with the zinc oxide surface. However, the kinetics were faster for acetic acid than acetaldehyde, which was explained in terms of an acetate-induced zinc dissolution process and a more complicated reaction path involved in the acetaldehyde case to form the zinc acetate surface species. Scanning electron microscopy indicated the formation of radially growing reaction products for acetic acid and filiform corrosion for acetaldehyde.

Ort, förlag, år, upplaga, sidor
Stockholm: KTH, 2005. s. vi, 57
Nyckelord
Corrosion science, laser spectroscopy, nonlinear optics
Nationell ämneskategori
Materialteknik
Identifikatorer
urn:nbn:se:kth:diva-455 (URN)91-7178-156-0 (ISBN)
Disputation
2005-10-28, M3, Brinellvägen 64, KTH, 10:00
Opponent
Handledare
Anmärkning
QC 20101029Tillgänglig från: 2005-10-20 Skapad: 2005-10-20 Senast uppdaterad: 2011-03-18Bibliografiskt granskad

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