Dresden 2017 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 58: Fluids and Interfaces II
CPP 58.5: Talk
Thursday, March 23, 2017, 11:45–12:00, ZEU 255
Influence of surface charge on interfacial water arrangement — •Lisa Dreier1,2, Ellen Backus1, and Mischa Bonn1 — 1Max Planck Institute for Polymer Research, Mainz, Germany — 2Graduate School Materials Science in Mainz, Mainz, Germany
For a charged surface in contact with an aqueous solution, the decay of the electric potential towards bulk liquid has been described by various models for the electric double layer. Usually, the electrostatic behavior of charged lipid-water interfaces is interpreted in the same way, even though the charge at these interfaces is highly localized. Here, we test experimentally to what extent electric double layer models for solid-liquid interfaces are applicable for lipid-water interfaces, especially very close to the surface in these systems. We study the water organization at the water-lipid interface using the non-linear optical spectroscopy vibrational Sum-Frequency Generation (SFG). Requiring that symmetry is broken, SFG is highly surface-selective, and provides the vibrational spectrum of specifically interfacial molecules; the SFG intensity can be related to the degree of interfacial water alignment. The charge carried by the interface orients interfacial water molecules. By mixing positively and negatively charged lipids, we can vary the surface charge at constant area per lipid molecule. Surprisingly, one can change the lipid layer composition, and thus the surface charge, dramatically without substantially influencing the arrangement of the water molecules. The SFG intensity, and thus the water orientation, responds in a remarkably strong nonlinear fashion to changes in the surface charge.