Interfacial water structure at surfactant concentrations below and above the critical micelle concentration as revealed by sum frequency generation vibrational spectroscopy

Nguyen, Khoi Tan, Nguyen, Anh V. and Evans, Geoffrey M. (2015) Interfacial water structure at surfactant concentrations below and above the critical micelle concentration as revealed by sum frequency generation vibrational spectroscopy. Journal of Physical Chemistry C, 119 27: 15477-15481. doi:10.1021/acs.jpcc.5b04416


Author Nguyen, Khoi Tan
Nguyen, Anh V.
Evans, Geoffrey M.
Title Interfacial water structure at surfactant concentrations below and above the critical micelle concentration as revealed by sum frequency generation vibrational spectroscopy
Journal name Journal of Physical Chemistry C   Check publisher's open access policy
ISSN 1932-7455
Publication date 2015-07-09
Year available 2015
Sub-type Article (original research)
DOI 10.1021/acs.jpcc.5b04416
Open Access Status Not yet assessed
Volume 119
Issue 27
Start page 15477
End page 15481
Total pages 5
Place of publication Washington, DC United States
Publisher American Chemical Society
Language eng
Abstract Interfacial water in close proximity to an adsorbed surfactant layer plays an important role in many areas. Here, we systematically investigate the interfacial water structure at the adsorption layer of cetyltrimethylammonium bromide (CTAB) from low concentrations to its critical micelle concentration. Our sum frequency generation (SFG) spectroscopy results show that, with increasing CTAB concentration, the water SFG signals first increase, reaching maximum intensities at 0.1 mM, and then drop, whereas the ppp SFG signals of the terminal-methyl asymmetric stretch reach maximum intensities and saturate at 1 mM, which is the critical micelle concentration of CTAB. Our analysis reveals that the interfacial water layer adopts the most orderly arrangement when the interfacial potential of the adsorption layer reaches saturation and not at the surfactant concentration of adsorption saturation. Most importantly, our SFG data provide direct evidence for the antagonistic effects of the interfacial potential and thickness compression of the electrostatic field of the surfactant adsorption layer, leading to the strongest water SFG signals at 0.1 mM. Below 0.1 mM, the increased interfacial potential can have a pronounced effect on the increase of the overall dipole moment of the interfacial water layers. Above 0.1 mM, the decreased Debye screening length significantly reduces the water dipole moment. Finally, the newly proposed adsorption model cannot explain our SFG results.
Keyword Chemistry, Physical
Nanoscience & Nanotechnology
Materials Science, Multidisciplinary
Chemistry
Science & Technology - Other Topics
Materials Science
Q-Index Code C1
Q-Index Status Confirmed Code
Grant ID LE0989675
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: School of Chemical Engineering Publications
Official 2016 Collection
 
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