Intermolecular Interactions at the Interface Quantified
by Surface-Sensitive Second-Order Fermi Resonant Signals
- Publication date
- Publisher
Abstract
Accurate determination of intermolecular
interaction forces at
the surface and the interface is essential to identify the nature
of interfacial phenomena such as absorption, interfacial assembly,
and specific ion effect, but it still represents a major technical
challenge. In this study, we proposed a novel method to deduce the
interfacial interaction forces by using surface-sensitive second-order
Fermi resonant signals, generated in sum frequency generation vibrational
spectroscopy (SFG-VS). By investigating the influence of lipid chain
length and intermolecular distance on the Fermi resonant signals of
phospholipid monolayer at the air/CaF<sub>2</sub> surface and the
air/water interface, a linear correlation between the Fermi resonant
intensity ratio and the dominated interactions in the lipid monolayer
has been observed. It implies that the amplitude of the intensity
ratio can be used as an effective <i>in situ</i> vibrational
optical ruler to characterize the total intermolecular interaction
forces at the surface and the interface. Such a relationship further
enables us to elucidate the specific ion effects on the interfacial
interactions, allowing us to identify different contributions from
van der Waals, electrostatic, and hydration interactions. This study
clearly demonstrates the power of the second-order Fermi resonant
signals for evaluating the interfacial interaction forces <i>in</i> <i>situ</i> and in real time