Time：3:00 p.m., September 8th, 2015.
Location: Meeting Room 300, State Key Laboratory of Molecular Reaction Dynamics (36#)
Lecturer: Dr. Ellen H.G. Backus
Max Planck Institute for Polymer Research, Mainz, Germany
Biography:
Ellen Backus obtained her PhD in physical chemistry in 2005 in the group of M. Bonn and A. Kleyn at the University of Leiden in the Netherlands. Subsequently, she worked as a PostDoc in the group of P. Hamm at the University of Zurich in Switzerland, followed by an independent PostDoc in the Netherlands at the AMOLF institute (group of H. Bakker) in Amsterdam. Since February 2012 she has been working as a group leader at the Max Planck Institute for Polymer Research in the department of M. Bonn. Her current research focuses on studying the structure and dynamics of water at interfaces using (multidimensional) sum-frequency generation spectroscopy.
Abstract:
At an interface the hydrogen bonding network of water is abruptly broken. What is the effect of this on the structure and dynamics of water at interfaces? In this talk we will look at water at two different types of interfaces by using sum-frequency generation spectroscopy with an infrared and visible laser beam to obtain the vibrational spectrum of the interface.
In the first part we look at water flowing underneath a solid surface – e.g. model systems for water in riverbeds, rain drops falling on the ground, and pouring water in a glass. The influence of this motion on the structure of water at the interface is unclear. We will show for calcium fluoride and silicondioxide interfaces that flow results in a reversible change of the surface charge and thus an alignment of the water molecules present at the interface. Moreover, we show that flow can invert the orientation of water molecules at the interface [1].
In the second part, the structure and structural dynamics of water in contact with two different surfactant monolayers is explored using ultrafast time resolved 2-dimensional sum frequency generation spectroscopy (2DSFG). Water in contact with both the negatively charged industrial surfactant sodium dodecyl sulfate (SDS), and the positively charged lipid 1,2-dipalmitoyl-3-trimethylammonium-propane (DPTAP) displays remarkably fast energy transfer, as is reflected by the loss of frequency correlations on sub-picosecond timescales. Moreover, for the SDS interface two coupled types of O-H vibrations are observed; this is in marked contrast to the pure air-water interface where only one type of water has been observed. The results have given remarkable insight into how the interfacial hydrogen bonding network is influenced by the presence of a surfactant/membrane monolayer.
[1] D. Lis et al., Science 344, 1138 (2014)
Contact: Group 1102, Chuanyao Zhou (9701)