Hannover 2016 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 19: Posters 4: Novelties in Molecular Physics: Femtosecond Spectroscopy, Molecular Clusters, Cold Molecules and Helium Droplets

MO 19.3: Poster

Donnerstag, 3. März 2016, 16:30–19:00, Empore Lichthof

Heterodyne-detected Sum Frequency Generation Spectroscopy of Polyacrylic Acid at the Air/Water- Interface — •Patrick Balzerowski², Konrad K. Meister¹, Jan Versluis¹, and Huib J. Bakker¹ — ¹FOM-Institute for Atomic and Molecular Physics AMOLF, Amsterdam, The Netherlands — ²Institute for Physical Chemistry II, Ruhr-Universität Bochum, Bochum, Germany

Here we present our findings on the conformational and hydration behavior of polyacrylic acid (PAA) at the air/water interface studied by heterodyne-detected vibrational sum frequency generation spectroscopy (HDVSFG). The amount of adsorption at the water/air interface and the influence of PAA on the water structure at the interface are found to be highly dependent on the degree of ionization (acid dissociation) of the carboxylic acid groups. At a low degree of ionization PAA is surface active and the spectral features suggest that PAA remains in a dense packing arrangement with intrachain hydrogen bonds. The HDVSFG spectra clearly show that the interfacial water molecules have a net orientation with their OH groups pointing towards the surface. Increasing the ionization degree of the carboxylic acid groups leads to an increase of the negative charge and to a break-up of the intrachain hydrogen bonds. This increase in negative charge comes along with an increase of the VSFG signal of the interfacial water molecules due to their enhanced orientation. At ionization degrees of α > 0.203 PAA loses its enhanced surface propensity and is well desolved in the bulk. Changing the ionic strength of the solution by addition of NaCl is observed to lead to a recurrence of PAA to the interface.