We utilize ambient pressure x-ray photoelectron spectroscopy (APXPS) to probe the composition of the liquid/vapor interface of a solution micro-jet (25 micron diameter).  The XPS spectra provide information on the composition and local chemical environment of the solution surface.  Experiments carried out at synchrotron sources (ALS and BESSY II) allow us to vary the photon energy used in the XPS experiment—thus providing spectra over a range of photoelectron kinetic energies.  Varying the photoelectron kinetic energy changes the “probe depth” of the experiment into the sample—thus providing information on the concentration profile of solutes into the solution.  A variety of ionic and neutral solutes have been studied in water solutions.  Highly miscible solutions (e.g. acetonitrile in water and ethanol in water) and less soluble solutes (e.g. organosulfur compounds—DMS, DMSO) have been studied.  In all cases we observe surface segregation of the organic solute at low bulk concentrations.  Details of the density profiles of a number of organic solutes in water will be presented along with MD simulations that provide insight into the solvation details that drive surface segregation in many systems.  Recent experiments in which we utilize a two channel microfluidic mixing system to mix two solutions just prior to the formation of the free jet, and thus initiating a chemical reaction, will also be described. <br/>

Composition and chemistry of liquid/vapor interfaces studied by liquid-jet x-ray photoelectron spectroscopy and molecular dynamics simulations

2019 Spring National Meeting

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