Investigations of the Structure and Hydrogen Bonding of Water Molecules at Liquid Surfaces by Vibrational Sum Frequency Spectroscopy

1998 ◽  
Vol 102 (20) ◽  
pp. 3847-3861 ◽  
Author(s):  
D. E. Gragson ◽  
G. L. Richmond
Keyword(s):  
Hydrogen Bonding ◽  
Water Molecules ◽  
Sum Frequency ◽  
Sum Frequency Spectroscopy ◽  
Vibrational Sum Frequency Spectroscopy ◽  
Liquid Surfaces

On the Charging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy

2018 ◽  
Author(s):  
Eric Tyrode ◽  
Robert W. Corkery
Keyword(s):  
Carboxylic Acid ◽  
Langmuir Monolayers ◽  
Ion Concentration ◽  
Double Layers ◽  
Water Molecules ◽  
Diffuse Double Layer ◽  
Sum Frequency ◽  
Monovalent Ions ◽  
Sum Frequency Spectroscopy ◽  
Vibrational Sum Frequency Spectroscopy

The charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate stretching modes. The charging behaviour was found to be in excellent agreement with that predicted by Gouy-Chapman theory using a thermodynamic pKa of 5.1 ± 0.2. This resulted in an apparent pKa of ~10.8 when the only ions present in solution were those associated with adjusting the pH. Water molecules with a preferred orientation in the immediate surface region were found to primarily interact with the uncharged carboxylic acid moiety, decreasing in number as the monolayer further deprotonated. Contributions from water molecules in the diffuse double layer, partly aligned by the exponentially decaying surface electric field, closely followed the predictions of a recently proposed theoretical framework that accounts for interference and screening effects. Finally, the charging of the monolayer was experimentally found to be independent of the identity of either the monovalent cation (i.e., Li+, Na+, Rb+) or anion (i.e., F-, Cl-, I-) at low salt concentrations.

On the Charging of Carboxylic Acid Monolayers with Monovalent Ions at Low Ionic Strengths: Molecular Insight Revealed by Vibrational Sum Frequency Spectroscopy

2018 ◽  
Author(s):  
Eric Tyrode ◽  
Robert W. Corkery
Keyword(s):  
Carboxylic Acid ◽  
Langmuir Monolayers ◽  
Ion Concentration ◽  
Double Layers ◽  
Water Molecules ◽  
Diffuse Double Layer ◽  
Sum Frequency ◽  
Monovalent Ions ◽  
Sum Frequency Spectroscopy ◽  
Vibrational Sum Frequency Spectroscopy

The charging of arachidic acid Langmuir monolayers as a function of subphase pH and monovalent ion concentration below 100 mM was investigated using vibrational sum frequency spectroscopy. Molecular information was obtained by targeting the vibrational modes of the carboxylic acid headgroups, alkyl chains, and water molecules in the immediate surface and diffuse double layers. The surface charge in the monolayer was experimentally determined by monitoring the hydrated carboxylate stretching modes. The charging behaviour was found to be in excellent agreement with that predicted by Gouy-Chapman theory using a thermodynamic pKa of 5.1 ± 0.2. This resulted in an apparent pKa of ~10.8 when the only ions present in solution were those associated with adjusting the pH. Water molecules with a preferred orientation in the immediate surface region were found to primarily interact with the uncharged carboxylic acid moiety, decreasing in number as the monolayer further deprotonated. Contributions from water molecules in the diffuse double layer, partly aligned by the exponentially decaying surface electric field, closely followed the predictions of a recently proposed theoretical framework that accounts for interference and screening effects. Finally, the charging of the monolayer was experimentally found to be independent of the identity of either the monovalent cation (i.e., Li+, Na+, Rb+) or anion (i.e., F-, Cl-, I-) at low salt concentrations.

Effects of Reorientation in Vibrational Sum-Frequency Spectroscopy†

2007 ◽  
Vol 111 (25) ◽  
pp. 8902-8915 ◽  
Author(s):  
John T. Fourkas ◽  
Robert A. Walker ◽  
Suleyman Z. Can ◽  
Erez Gershgoren
Keyword(s):  
Sum Frequency ◽  
Sum Frequency Spectroscopy ◽  
Vibrational Sum Frequency Spectroscopy
Sign in / Sign up

Export Citation Format

Share Document