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Study of the adsorption of sodium dodecyl sulfate (SDS) at the air/water interface: targeting the sulfate headgroup using vibrational sum frequency spectroscopy
KTH, Skolan för kemivetenskap (CHE), Kemi, Korrosionslära.
KTH, Skolan för kemivetenskap (CHE), Kemi, Ytkemi.
2005 (engelsk)Inngår i: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 7, nr 13, s. 2635-2640Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

The surface sensitive technique vibrational sum frequency spectroscopy (VSFS), has been used to study the adsorption behaviour of SDS to the liquid/vapour interface of aqueous solutions, specifically targeting the sulfate headgroup stretches. In the spectral region extending from 980 to 1850 cm(-1), only the vibrations due to the SO3 group were detectable. The fitted amplitudes for the symmetric SO3 stretch observed at 1070 cm(-1) for the polarization combinations ssp and ppp, were seen to follow the adsorption isotherm calculated from surface tension measurements. The orientation of the sulfate headgroup in the concentration range spanning from 1.0 mM to above the critical micellar concentration ( c. m. c.) was observed to remain constant within experimental error, with the pseudo-C-3 axis close to the surface normal. Furthermore, the effect of increasing amounts of sodium chloride at SDS concentrations above c. m. c. was also studied, showing an increase of approximately 12% in the fitted amplitude for the symmetric SO3 stretch when increasing the ionic strength from 0 to 300 mM NaCl. Interestingly, the orientation of the SDS headgroup was also observed to remain constant within this concentration range and identical to the case without NaCl.

sted, utgiver, år, opplag, sider
2005. Vol. 7, nr 13, s. 2635-2640
Emneord [en]
Adsorption, Air, Sodium Chloride, Sodium Dodecyl Sulfate, Spectrophotometry, Infrared, Surface Properties, Water
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-24909DOI: 10.1039/b505219jISI: 000229978300014Scopus ID: 2-s2.0-22244490701OAI: oai:DiVA.org:kth-24909DiVA, id: diva2:354188
Merknad
QC 20100930Tilgjengelig fra: 2010-09-30 Laget: 2010-09-30 Sist oppdatert: 2017-12-12bibliografisk kontrollert
Inngår i avhandling
1. Vibrational Sum Frequency and Infrared Reflection/Absorption Spectroscopy Studies of the Air/Liquid and Liquid/Metal Interfaces
Åpne denne publikasjonen i ny fane eller vindu >>Vibrational Sum Frequency and Infrared Reflection/Absorption Spectroscopy Studies of the Air/Liquid and Liquid/Metal Interfaces
2005 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
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.

sted, utgiver, år, opplag, sider
Stockholm: KTH, 2005. s. vi, 57
Emneord
Corrosion science, laser spectroscopy, nonlinear optics
HSV kategori
Identifikatorer
urn:nbn:se:kth:diva-455 (URN)91-7178-156-0 (ISBN)
Disputas
2005-10-28, M3, Brinellvägen 64, KTH, 10:00
Opponent
Veileder
Merknad
QC 20101029Tilgjengelig fra: 2005-10-20 Laget: 2005-10-20 Sist oppdatert: 2011-03-18bibliografisk kontrollert

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