Raman and NMR spectroscopy study of liquid crystalline ionogel phase in ionic liquid/H2O mixtures: The states of water

The Raman spectra of 1-decyl-3-methyl-imidazolium bromide ([C10mim][Br]) aqueous solutions have been measured while continuously increasing the water content in the system (0-100%). Principal component (PC) and 2D Raman correlation (2DCOR) analysis has been carried out, the main attention concentrating to the region of O-H stretching vibrations at 3100-3800 cm−1. The band structure has been resolved in the loadings on PC1 and PC2 as well as in 2DCOR spectra. It indicates the presence in the studied system of several nonequivalent states of water. Various states of water have been also revealed in the 1H NMR spectra. They have been assigned to non-bonded or weakly H-bonded water molecules, those involved in the fast isotropic reorientational motion as well as in the H-bond exchange processes and finally - water in the LC ionogel structures. The last contributes the 1H NMR line shape typical for anisotropic liquids with zero biaxiality (asymmetry) of magnetic shielding and the chemical shift anisotropy of ca 0.6 ppm. The borders of the liquid crystalline (LC) ionogel phase have been determined using the concentration dependence of the integral intensities of Raman bands and the scores on PC1.