Quantifying Surfactant Alkyl Chain Orientation and Conformational Order from Sum Frequency Generation Spectra of CH Modes at the Surfactant-Water Interface.
We combine second-order nonlinear vibrational spectroscopy and quantum-chemical calculations to quantify the molecular tilt angle and the structural variation of a decanoic acid surfactant monolayer on water. We demonstrate that there is a remarkable degree of delocalization of the vibrational modes along the backbone of the amphiphilic molecule. A simulation-based on modeled sum frequency generation (SFG) spectra offers quantitative insights into the disorder of surfactant monolayers at the water-air interface. It is shown that an average of one gauche defect in the alkyl chain suffices to give rise to the methylene stretch intensity similar in magnitude to the methyl stretch.
Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Michael
M
Schleeger
Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Yuki
Y
Nagata
Department of Molecular Spectroscopy, Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany.
Mischa
M
Bonn
SFG; conformational order; delocalization; density functional theory; detergent; molecular tilt angle; self-assembled monolayer