Liquid-vapor (especially aqueous-vapor) interfaces play a major role in atmospheric science, for example in the interaction of oceans with the atmosphere, in aqueous aerosols where they govern important chemical reactions, or in the evaporation of lakes and reservoirs. Sparely soluble, amphiphilic organic molecules (e.g. long chain fatty acids) tend to accumulate at the surface of aqueous solutions and can change dramatically the properties of the interface. One of the crucial steps towards a better understanding of the effect of surfactants is to obtain molecular-scale information on the arrangement and behavior of these molecules at the interface.<br/><br/>Here we present an investigation of long-chain fatty acids in aqueous solutions, where photoemission spectroscopy is coupled with a liquid microjet. We show how the measurement of photoelectron angular distributions (PADs, see fig. 1) in XPS (X-ray photoelectron spectroscopy), a so far little explored parameter, can provide information on the position of surfactant molecules relative to the interface. We also present UPS (Ultraviolet photoelectron spectroscopy) measurements on the same kind of solutions and show that in addition to exploring adsorption behavior of the surfactants, we can also monitor changes in water evaporation rates and the presence of surface dipoles due to the surfactants.

Investigating surfactants at the liquid-vapor interface using liquid jet photoemission spectroscopy

ACS Spring Meeting 2021

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