Change search
ReferencesLink to record
Permanent link

Direct link
Vibrational Sum Frequency Spectroscopy Studies at the Air-Liquid Interface
KTH, School of Chemical Science and Engineering (CHE), Chemistry.
2005 (English)Doctoral thesis, monograph (Other scientific)
Abstract [en]

In this thesis the structure and hydration of small organic and amphipilic compounds adsorbed at the air-liquid interface, have been studied using the nonlinear optical technique Vibrational Sum Frequency Spectroscopy (VSFS). The second order nature of the sum frequency process makes this technique particularly surface sensitive and very suitable for interfacial studies, as molecules at the surface can be distinguished even in the presence of a vast excess of the same molecules in the bulk. Particular emphasis was given to the surface water structure and how it is affected by the presence of small model compounds such as acetic acid and formic acid, and also non-ionic surfactants with sugar based and ethylene oxide based polar headgroups. Understanding the structure of water at these interfaces is of considerable fundamental importance, and here VSFS provided unique information. Upon addition of tiny amounts of these surface active compounds, the ordered surface structure of water was found to be significantly perturbed, as revealed by the changes observed in the characteristic spectroscopic signature of the dangling OH bond of water molecules, which vibrate free in air and are present in the top monolayer. Dramatic differences between the different compounds were also observed in the bonded OH region, providing a valuable insight into the hydration of polar groups at interfaces. Additionally, by employing different polarization combinations of the laser beams involved in the sum frequency process, information about the different water species present at the surface and their average orientation were extracted. In particular an unusual state of water was found with a preferred orientation in a non-donor configuration in close proximity to the hydrophobic region formed by the hydrocarbon tails of the surfactant molecules.

The conformation and orientation of the different adsorbates were also characterized, targeting their specific vibrational frequencies. Noteworthy is the orientation of the fluorocarbon chain of ammonium perfluorononanoate (APFN), which in contrast to the hydrocarbon chains of the other surfactant molecules studied, remained constant over a wide range of surface densities. This behaviour was also observed for the anionic headgroup of sodium dodecyl sulphate (SDS). Other interesting findings were the formation of a cyclic dimer bilayer at the surface of concentrated aqueous solutions of acetic acid and the water structuring effect induced by poly(ethylene-oxide) headgroups, in spite of being themselves disordered at the air-liquid interface.

Place, publisher, year, edition, pages
Trita-YTK, ISSN 1650-0490 ; 0504
Keyword [en]
Sum Frequency Generation, SFG, VSFS, surfactant, adsorption, water, surface structure, hydration, surface tension, fluorosurfactants, liquid-air interface, poly(ethylene oxide) surfactants, surface molecular orientation, acetic acid.
National Category
Physical Chemistry
URN: urn:nbn:se:kth:diva-440ISBN: 91-7178-159-5OAI: diva2:12145
Public defence
2005-10-14, E2, Lindstedsvägen 3 Entrepl, Stockholm, 10:00
Available from: 2005-09-29 Created: 2005-09-29 Last updated: 2012-03-21

Open Access in DiVA

fulltext(1302 kB)1176 downloads
File information
File name FULLTEXT01.pdfFile size 1302 kBChecksum MD5
Type fulltextMimetype application/pdf

Search in DiVA

By author/editor
Tyrode, Eric
By organisation
Physical Chemistry

Search outside of DiVA

GoogleGoogle Scholar
Total: 1176 downloads
The number of downloads is the sum of all downloads of full texts. It may include eg previous versions that are now no longer available

Total: 833 hits
ReferencesLink to record
Permanent link

Direct link