The presence and behavior of polyelectrolytes at oil-water interfaces is important to the workings of a large number of processes including environmental remediation and biological systems. An interfacial sensitive technique, vibrational sum-frequency spectroscopy (VSFS) can provide insight to how polyelectrolytes reside at oil-water interfaces. The nature of the VSFS response in experiments and the complexity of the systems involved make it impossible to directly access some specific and desired molecular information. To obtain detailed molecular information, classical molecular dynamics calculations for a set of polyelectrolytes at oil-water interfaces are performed. The veracity of the dynamics calculations is supported by calculation of VSFS spectra for direct comparison with experiment. Molecular orientations and conformations from classical molecular dynamics as well as second order linear susceptibilities from time dependent density functional theory are used to determine theoretical VSFS spectra. Previous studies have highlighted the need for inclusion of anharmonic effects, which are accounted for in the density functional theory calculations. Molecular dynamics and VSFS spectra calculations are performed for a variety of protonation states and in the presence of aqueous salts.  With this approach, a direct link is formed between experimental measurements and theoretical calculations that provide a view of specific molecular behavior that may not be probed experimentally.

Polyelectrolyte wants a surface: Modeling vibrational sum-frequency spectra of polyelectrolytes at oil-water interfaces

247th National Meeting (2014)

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