Water-in-oil (w/o) emulsions are of great interest in many areas including food technology and the oil and gas industry. However, the molecular mechanisms that lead to a stable emulsion are yet to be fully understood. In this article, the potential of attenuated total reflection (ATR) infrared (IR) spectroscopy for studying the influence of an emulsifier on the molecular water structure in a thin layer at the w/o interface is demonstrated. For this purpose, IR spectra from a bilberry extract w/o emulsion are analyzed. The thickness of the probed water layer is estimated to be below 0.5 μm, which is well below the droplet diameter. The IR spectra recorded in aqueous solution and the w/o emulsion reveal a strengthening of the intramolecular covalent O–H bonds in the presence of the emulsifier, which in turn indicates a change in the hydrogen bond network in terms of weakening the intermolecular interactions in the water layer at the interface.
Johannes Kiefer, Kerstin Frank, and Heike P. Schuchmann, "Attenuated Total Reflection Infrared (ATR-IR) Spectroscopy of a Water-in-Oil Emulsion," Appl. Spectrosc. 65, 1024-1028 (2011)