Surface–Bulk Vibrational Correlation Spectroscopy

Abstract

Homo- and heterospectral correlation analysis are powerful methods for investigating the effects of external influences on the spectra acquired using distinct and complementary techniques. Nonlinear vibrational spectroscopy is a selective and sensitive probe of surface structure changes, as bulk molecules are excluded on the basis of symmetry. However, as a result of this exquisite specificity, it is blind to changes that may be occurring in the solution. We demonstrate that correlation analysis between surface-specific techniques and bulk probes such as infrared absorption or Raman scattering may be used to reveal additional details of the adsorption process. Using the adsorption of water and ethanol binary mixtures as an example, we illustrate that this provides support for a competitive binding model and adds new insight into a dimer-to-bilayer transition proposed from previous experiments and simulations.

Self-assembly of l-phenylalanine amino acid: electrostatic induced hindrance of fibril formation

“…ATR-FTIR spectroscopy is an excellent and a powerful linear vibrational spectroscopic tool to probe the structural composition of moieties present in the bulk up to a probing length in the order of a few micrometer range. 32,40,[42][43][44][45][46] The details about the mathematical formulation related to ATR correction and penetration depth of evanescent wave are provided in the ESI section and in Fig. S1.…”

“…There is a change in penetration depth of evanescent wave in sample with respect to the wavelength of radiation which may alter the relative peak heights and positions of the absorption spectrum. 40,41 In order to address this problem in the present work we have treated our data with the ATR correction factor and the details of this method are briey discussed in ESI section. †…”

Surface Structure of Acrylate Polymer Adhesives

“…Post-processing included Norton-Beer apodization, 4 levels of zerofilling, and a standard ATR correction to provide the transmission-equivalent absorption coefficient proportional to the imaginary component of the linear susceptibility χ (1) . 25 No evidence of anisotropy was found over the evanescent wave penetration depth of the mid-IR beam, so only p-polarized spectra are considered for subsequent analysis as they displayed higher absorbance. In general, the polarization of a material P may be expressed in terms of susceptibility tensor elements…”

Adsorption of heptane–toluene binary mixtures on a hydrophobic polymer surface

“…If χ (2) 2 spectra were used in the 2DCOS, artifacts from the changing interference between neighbouring modes would obscure these trends. 62,63 We have used these general principles to determine that there is only a small change in orientation of toluene as their surface composition changes, and no obvious preference for either molecule on a perfluorinated hydrophobic surface. These results, together with previous understanding of the structure at hydrophilic surfaces, provide a foundation for understanding adsorption of real and model constituents such as asphthalenes, and the further optimization of anti-fouling coatings for alkane-and aromatic-based fluids.…”

“…The homospectral correlation is generally more featurerich when applied to SFG data, as both the orientation and population of molecules at the surface contribute to the intensity of the vibrational modes. 38,[62][63][64] For example, a particular mode may have a strong IR transition dipole moment and Raman transition polarizability, but that part of the molecule may be oriented close to the plane of the surface, significantly reducing its intensity in the case of our C ∞v symmetry. The orientation and symmetry consideration is the dominant contribution to the SFG, as even molecules with strong IR and Raman transitions are SFG-silent in the bulk solution phase.…”