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Interfacial Water Features at Air-Water Interfaces as Influenced by Charged Surfactants.
Vu N T Truong1, Xuming Wang1, Liem X Dang2
1Department of Metallurgical Engineering, College of Mines and Earth Sciences , University of Utah , 135 South 1460 East , Rm 412, Salt Lake City , Utah 84112 , United States.
The Journal of Physical Chemistry. B
|February 16, 2019
Summary
Interfacial water molecules in sodium dodecyl sulfate (SDS) solutions exhibit higher order than in dodecyl amine hydrochloride (DDA) solutions. This is due to increased density, stronger hydrogen bonding, and better orientation at the SDS interface.
Area of Science:
- Physical Chemistry
- Surface Science
- Computational Chemistry
Background:
- Water molecules at air-water interfaces exhibit unique properties influenced by dissolved substances.
- Surfactants like sodium dodecyl sulfate (SDS) and dodecyl amine hydrochloride (DDA) significantly alter interfacial water structure.
- Understanding these alterations is crucial for various applications, including colloid science and materials engineering.
Purpose of the Study:
- To investigate and compare the structural features of interfacial water at air-water interfaces for anionic SDS and cationic DDA solutions.
- To elucidate the molecular-level mechanisms behind observed differences in interfacial water ordering.
- To enhance the fundamental understanding of interfacial water behavior in surfactant solutions.
Main Methods:
- Sum Frequency Generation (SFG) vibrational spectroscopy was employed to probe the structure of interfacial water.
- Molecular Dynamics Simulations (MDS) were utilized to analyze interfacial water density, hydrogen bonding, and orientation.
- Comparison of experimental SFG data with simulation results to validate findings.
Main Results:
- SFG spectra indicated significantly higher ordering of water molecules at the SDS-water interface compared to the DDA-water interface.
- MDS revealed that interfacial water in SDS solutions possesses higher number density and more robust hydrogen-bonding networks.
- Water molecules at the SDS interface demonstrated more orderly orientation relative to the surfactant head groups than at the DDA interface.
Conclusions:
- The anionic SDS interface promotes a more ordered interfacial water structure than the cationic DDA interface.
- Differences in water ordering are attributed to variations in water density, hydrogen bond connectivity, and orientation influenced by surfactant head groups.
- This study provides key insights into the distinct behaviors of interfacial water influenced by charged surfactants.
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