FTIR ATR analysis of the H bond network of water in branched polyethyleneimine/TEMPO oxidized cellulose nano fiber xerogels
The present paper reports a detailed experimental vibrational analysis, performed by Fourier transform infrared spectroscopy in attenuated total reflectance geometry (FTIR ATR) of water confined in the pores of cellulose nano sponges (CNSs) prepared using TEMPO oxidized and ultra sonicated cellulose nano fibers (TOUS CNFs) as three dimensional scaffolds, and branched polyethyleneimine (bPEI) as the cross linking agent. The analysis was carried out by varying hydration and cross linker amount, with the aim of achieving a deep understanding of how the hydrogen bond (H bond) scheme developed by engaged water molecules can play a role in the water adsorption process already observed at macroscopic level, furnishing at the same time evidence of a nano porous network for CNSs. In particular, the combined investigation of the FTIR ATR spectra of CNSs hydrated with H2O and D2O allowed for the selective analysis of vibrational modes of entrapped water molecules, namely O H stretching and HOH bending modes. As main result, a destructuring effect of hydration on the H bond pattern of interfacial water molecules is revealed, associated to structural modifications of the bPEI/TOUS CNFs network previously detected by small angle neutron scattering (SANS) technique. It turned out to be more relevant for low bPEI amounts. In addition, a supercooled behavior of entrapped water molecules is detected, supporting the idea of a nano confinement for water in these systems. The obtained information can be very helpful in view of all the possible applications of bPEI TOCNF sponges as efficient adsorbent materials, especially for water remediation.
Cellulose