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Crown ethers at the aqueous solution-air interface. Part 2. Electrolyte effects, ethylene oxide hydration and
Petru Niga1, C Magnus Johnson, Jeremy G Frey
1School of Chemical Science and Engineering, Royal Institute of Technology, Stockholm, 100 44, Sweden.
Physical Chemistry Chemical Physics : PCCP
|March 30, 2011
Summary
Vibrational Sum Frequency Spectroscopy revealed how crown ethers like 4-Nitro Benzo-15-Crown-5 affect the aqueous solution-air interface. Ordered water at the surface decreases with higher salt concentrations, indicating a charged interface.
Area of Science:
- Physical Chemistry
- Surface Science
- Spectroscopy
Background:
- Crown ethers, such as 4-Nitro Benzo-15-Crown-5 (NB15C5) and Benzo-15-Crown-5 (B15C5), are known to influence solution properties.
- The aqueous solution-air interface is a critical area for chemical and physical processes.
Purpose of the Study:
- To investigate the adsorption behavior of NB15C5 and B15C5 at the aqueous solution-air interface.
- To determine the orientation of NB15C5 molecules in response to varying concentrations.
- To probe the structure of water at the interface under different conditions.
Main Methods:
- Vibrational Sum Frequency Spectroscopy (VSFS) was utilized to analyze the adsorbing films.
- VSFS peak intensity ratios of CN and NO(2) vibrational modes were used to monitor NB15C5 orientation.
- Water of hydration was studied by varying crown ether and salt concentrations, as well as temperature.
Main Results:
- The presence of crown ether species significantly impacts the solution surface.
- NB15C5 orientation changes were observed with increasing solution concentration.
- Surface water ordering diminishes with increased bulk solution ionic strength.
Conclusions:
- The aqueous solution-air interface exhibits characteristics of a charged interface when influenced by crown ethers.
- Surface-associated water structure is sensitive to ionic strength, decreasing as it rises.
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