Vibrational signatures of the water behaviour upon confinement in nanoporous hydrogels

B. Rossi; V. Venuti; A. Mele; C. Punta; L. Melone; F. D'Amico; A. Gessini; V. Crupi; D. Majolino; F. Trotta; C. Masciovecchio

doi:10.1039/C5CP07936E

Vibrational signatures of the water behaviour upon confinement in nanoporous hydrogels

B. Rossi,*^ab V. Venuti,^c A. Mele,^d C. Punta,^d L. Melone,^de F. D'Amico,^a A. Gessini,^a V. Crupi,^b D. Majolino,^b F. Trotta^f and C. Masciovecchio^a

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* Corresponding authors

^a Elettra – Sincrotrone Trieste, Strada Statale 14 km 163.5, Area Science Park, 34149 Trieste, Italy
E-mail: barbara.rossi@elettra.eu

^b Department of Physics University of Trento and INSTM Local Unit, via Sommarive 14, 38123 Povo, Trento, Italy

^c Department of Physics and Earth Sciences, University of Messina, Viale Ferdinando Stagno D'Alcontres 31, 98166 Messina, Italy

^d Department of Chemistry, Materials and Chemical Engineering “G. Natta”, Politecnico di Milano and INSTM local unit, Piazza L. da Vinci 32, Milano, Italy

^e Università degli Studi e-Campus, Via Isimbardi 10, 22060 Novedrate, Como, Italy

^f Department of Chemistry, University of Torino, Via Pietro Giuria 7, 10125 Torino, Italy

Abstract

The fundamental question of how the reorganization of the hydrogen-bond (HB) network of water is influenced by the combination of nano-confinement and hydrophobic/hydrophilic solvation effects is addressed here using a spectroscopic study of water absorbed in a model, pH-sensitive polysaccharide hydrogel. The effects of temperature, hydration level and pH on the vibrational dynamics associated with the water molecules and the polymer skeleton are disentangled and analysed by a complementary and combined use of UV-Raman scattering and IR spectroscopy. The experimental data give evidence that the solvation effects in the hydrogel matrix are essentially dominated by the hydration of more hydrophobic parts of the polymer network, while the effect of pH on the HB reorganization of confined water molecules is found to be similar to that induced by cooling of the system. A tentative explanation of these results has been provided in terms of interplay between different kinds of interactions, i.e. hydrophobic vs. hydrophilic.

Physical Chemistry Chemical Physics

Vibrational signatures of the water behaviour upon confinement in nanoporous hydrogels

Abstract

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Vibrational signatures of the water behaviour upon confinement in nanoporous hydrogels

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