Search

23Na and 81Br NMR spin-lattice relaxation times and signal half widths (Δ1/2) have been measured in 3-methylpyridine (3MP)/H2O/NaBr mixture along T = 294 and 301 K isotherms gradually increasing the mass fractions of salt (X) up to the phase separation boundary. The extreme narrowing condition and thus 1/T1 = 1/T2 = πΔ1/2 was found to be valid in all cases. Discontinuous changes in slope of 1/T1,2 = f(X) were detected, and then corresponding points on the phase diagram (X, T) were attributed to the borderline between the molecular-ionic solution and the area of enhanced mesoscopic structuring. A very strong relaxation effect was observed for 81Br nuclei reaching relaxation rates of 14,000 s-1. 23Na and 81Br NMR relaxation data together with calculations of quantum chemistry model of electrical field gradient tensor evidence the migration of 3-methylpyridinium at increasing X from the anions hydration shells towards cations. An interchange from migration to steady distribution regimes is observed for anions and vice versa for cations at the borderline of the structured phase. [ABSTRACT FROM AUTHOR]

The temperature dependences of the narrow 1H NMR signals, in the temperature range below phase transition point from the plastic to brittle crystal for pivalic acid (PA) confined in the controlled pore size glasses with mean diameters of 7.9 and 23.9 nm have been investigated in order to determine the depression of the crystallization temperature and the pore size distribution parameters. The obtained parameters and the temperature dependences of the narrow 1H NMR signals in the solid phases of PA and other carboxylic acids (hexadecanoic (C16), heptadecanoic (C17), octadecanoic (C18), nonadecanoic (C19)) have been used for studying the pore size distributions appeared during the natural crystallization. It was found that the pore size distribution for the even-numbered acids (C16 and C18) is spread over much wider range of the sizes comparing with those for odd-numbered acids (C17 and C19). The maximal value of the pore radius R = 40.4 nm has been found at the temperature just below the melting point of C18, which is about eight times bigger than that found for C17. [ABSTRACT FROM AUTHOR]

Abstract: 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 3100–3800cm−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 0.6ppm. 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. [Copyright &y& Elsevier]