Research Topics

The current focus of the research group is on understanding the structure and dynamics of interfacial water. Amongst others, the properties of water adjacent to hard and soft interfaces are relevant for applications in electrochemistry, folding of macromolecules, and catalysis. In order to study selectively water molecules at interfaces, we use nonlinear optical spectroscopic techniques. In these methods no signal is generated from centrosymmetric media. At interfaces the bulk symmetry is broken. Therefore, selectively interfacial molecules can be studied. In my group we use predominantly the nonlinear method sum frequency generation (SFG) spectroscopy. Here, one of the incoming laser beams is in the infrared region.

If the infrared light is in resonance with a molecular vibration the signal is strongly enhanced. In this way the vibrational spectrum of interfacial molecules is obtained. The spectrum delivers not only information about which molecules are present, but also about their environment and orientation. In the recent years, the technique developed into phase, time, and multidimensional spectroscopy. With the phase resolved SFG method the orientation of molecules can be unraveled. Time resolved SFG delivers information about vibrational energy relaxation, rotational dynamics, and reaction pathways. Using these state of the art methods, the research group is devoted to understanding the molecular scale structure, relaxation dynamics, and reactivity of interfacial molecules. Besides our main research focus on water at interfaces, we are also interested in the structure, orientation and dynamics of molecules like surfactants, peptides, and organic acids.

Liquid interface

Part of the research in the group is devoted to the water-air interface with and without surfactants on top. We are interested in studying how for example ions change the structure and dynamics of interfacial water molecules, as physical and chemical processes occurring at aqueous interfaces have been shown to play a prominent role in a variety of fields ranging from chemistry of atmospheric aerosols and heterogeneous catalysis to biophysics and biochemistry. Knowledge of the molecular interfacial structure and dynamics of water interfaces is essential not only for a fundamental understanding of this ubiquitous liquid, but also for the many environmental and biophysical systems in which aqueous interfaces appear. In other projects we use a monolayer of surfactant molecules as model systems for cell membranes. Subsequently, we study the effect of ions on the surfactant alignment and on the water next to the surfactant headgroups. Moreover, by injecting for example peptides or dendrimers into the subphase we can monitor the interaction between these molecules and the surfactant.