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Updated: May 26, 2026

Multimodal Nonlinear Hyperspectral Chemical Imaging Using Line-Scanning Vibrational Sum-Frequency Generation Microscopy
Published on: December 1, 2023
Combining gravimetric and vibrational spectroscopy measurements to quantify first- and second-shell hydration layers
Pellegrino Musto1, Giuseppe Mensitieri, Marino Lavorgna
1Institute of Chemistry and Technology of Polymers, National Research Council of Italy, Via Campi Flegrei 34, Olivetti Buildings, 80078, Pozzuoli (NA), Italy. pellegrino.musto@ictp.cnr.it
Abstract:
In-situ Fourier transform infrared (FTIR) measurements have been carried out at different relative pressures of water vapor to study the H(2)O diffusion in three polyimides differing in their molecular structure and fluorine substitution. Spectral data have been analyzed by difference spectroscopy, least-squares curve fitting, and two-dimensional (2D) correlation spectroscopy, which provided molecular level information on the diffusion mechanism. In particular, two distinct water species were identified corresponding, respectively, to the first and second-shell hydration layers. The spectroscopic analysis demonstrated that the relative population of these species is a function of the total water content in the system. A method has been devised to quantify the water concentration in the two hydration layers, based on a combination of spectroscopic and gravimetric data. The results have been compared with those from an earlier spectroscopic approach reported in the literature and based on the analysis of the carbonyl region.
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