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Polymer coatings offer a means to modulate the adsorption of molecules onto solid surfaces by offering a surface functionality, charge, roughness, and hydrophobicity that is different from the underlying substrate. One application is to provide anti-fouling functions for metal surfaces. Understanding solvent-surface interactions is an essential component to gaining mechanistic insight into the adsorption process. In this work, we study the adsorption of toluene–heptane binary mixtures onto a perflurorinated polymer surface. We use a combination of IR absorption and Raman scattering spectroscopy to study the mixture in the bulk phase, and surface-specific visible-infrared sum-frequency generation to probe the surface layers. Through the use of homo- and heterospectral two-dimensional correlation spectroscopy, we conclude that the adsorption of the two solvents is reversible and that the surface structure is generally independent of the surface composition, with a small change in toluene orientation as the toluene content increases. We also find that the hydrophobic fluropolymer has very little preference for either solvent, similar to previous studies on hydrophilic surfaces. [ABSTRACT FROM AUTHOR]

Vibrational sum-frequency generation spectroscopy is a valuable probe of surface structure, particularly when the same molecules are present in one of the adjacent bulk solid or solution phases. As a result of the non-centrosymmetric requirement of SFG, the signal generated is a marker of the extent to which the molecules are ordered in an arrangement that breaks the up-down symmetry at the surface. In cases where the accompanying changes in the bulk are of interest in understanding and interpreting the surface structure, simultaneous analysis of the bulk IR absorption or bulk Raman scattering is helpful, and may be used in heterospectral surface-bulk two-dimensional correlation. We demonstrate that, in such cases, generating a new type of bulk spectrum that combines the IR and Raman amplitudes is a better candidate than the individual IR and Raman spectra for the purpose of correlation with the SFG signal. [ABSTRACT FROM AUTHOR]