Proton NMR relaxation times allow to study molecular correlations within water-methanol solutions.
Mallamace D., Corsaro C., Fazio E., Mallamace F., Stanley H.E.
VI - Fisica applicata, acceleratori e beni culturali
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The dynamic behavior of water-methanol solutions has been studied by means of NMR spectroscopy as a function of concentration and temperature, including the supercooling regime. In particular, the thermal evolution of the longitudinal or spin-lattice and of the transverse or spin-spin relaxation times, $T_1$ and $T_2$, respectively, has been investigated at different methanol molar fractions. In such a way, the reciprocal influences of hydrophobic effects on the water properties as well as that of the hydrophilicity on the solute (through hydrogen bond interactions) have been pointed out by means of a single characteristic correlation time $\tau_c$. This is interesting taking into account that this correlation time reflects all local structural configurations and characterizes the corresponding dynamics. One of the main result of this NMR investigation shows how the temperature rise progressively reduces the lifetime of the hydrogen bond interactions with consequent decoupling in the dynamic modes of the system. Specifically, at temperatures above about 265 K, hydrophobicity becomes progressively stronger and governs the physical properties of the solutions.