Modelling the interplay between covalent and physical interactions in cyclodextrin-based hydrogel: effect of water confinement

Abstract

The vibrational dynamics of a new class of cyclodextrin-based hydrogel is explored in depth here with the aim to clarify the intimate relationship between the structural and functional properties of these innovative polymeric materials. The thorough quantitative analysis of the FTIR-ATR and Raman spectra of the hydrogel obtained by swelling of cross-linked polymers of cyclodextrins with heavy water is performed in the wavenumber range between 1600 and 1800 cm⁻¹ by using best-fitting and deconvolution procedures. The use of D₂O instead of H₂O allowed us to separately examine in the vibrational spectra of the hydrogel the CO stretching bands assigned to the polymer network and the bending mode of engaged water molecules, giving the possibility to explore the structural changes occurring in the polymer network during the hydration process. The experimental findings were interpreted in the light of a comprehensive model which attempts to understand how physical and covalent cross-links combine to determine the macroscopic properties of the gel, like its water holding capacity and the whole rigidity of the gel network. These results shed light on the complex interplay between physical and chemical interactions which yield the formation and stabilization of the hydrogel network, opening the possibility of a rational design of these innovative soft materials for specific technological applications.