Berlin 2018 – scientific programme
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CPP: Fachverband Chemische Physik und Polymerphysik
CPP 20: Poster Session I
CPP 20.56: Poster
Monday, March 12, 2018, 17:30–19:30, Poster A
Model-Free Thickness Determination of Nanoscale Foam Films using FTIR spectroscopy — •Eric Weißenborn and Björn Braunschweig — Institut für Physikalische Chemie, Westfälische Wilhelms-Universität Münster, Corrensstraße 28/30, 48149 Münster, Germany
The thin-film-pressure balance (TFPB) technique allows to determine intermolecular forces in free standing foam films. In order to calculate the surface potential of charged air/water/air interfaces, DLVO theory is applied where the correct size of the water core is extremely important. However, in the classical approach where the thickness is determined interferometrically, models of the adsorbate layer and its thickness have to be applied. In order to address the thickness of foam films, we have extended the abilities of a classical TFPB by combining interferometric UV/Vis spectroscopy and transmission IR spectroscopy in a single setup. Particularly, the coupling of a TFPB to a FTIR spectrometer allows to record IR spectra of foam films. From IR transmission spectra, we can not only accurately determine the foam film thickness as function of disjoining pressure by looking at the water O-H absorption bands, but can also determine their composition with the help of IR vibrational bands and their attribution to specific molecular vibrations. In order to demonstrate the proof of concept, we present disjoining pressure isotherms of cetyltrimethylammonium bromide (C16TAB) foam films at 0.9 and 0.1 mM concentrations and compare the film thicknesses from both interferometric UV/Vis and infrared spectroscopy.