Relaxation processes in water: Viscosity, self-diffusion, and spin-lattice relaxation. A kinetic model

Abstract

Experimental measurements of T1 for oxygen-17 water in n-heptane emissions were made in the supercooled region down to −31°C. The data were fit to the double exponential form of the rate equation with activation energies for the two processes of E1=11.85±0.57 and E2=3.54±0.08 kcal mole−1, respectively. Using transition state rate theory, activation entropies ΔS1*=35.3±2.3 and ΔS2*=4.63±0.25 cal deg−1 · mole−1 were calculated. It is proposed that both the low and high temperature reactions are kinetic processes. It is suggested that the large entropy term for the low temperature reaction indicates that the relaxation process involves the ``cooperative'' dissolution of a small cluster of hydrogen bonded molecules. An examination of the available data for viscosity and diffusion indicates that the high temperature relaxation process is the same as that for the rotational (T1) relaxation. It is suggested that this process involves the breaking of a single hydrogen bond. The question of whether the low temperature processes for viscous flow, diffusion, and rotational relaxation are related is discussed.

Water–Surfactant Contact Studied by19F–1H Heteronuclear Overhauser Effect Spectroscopy

“…In our analysis (see below) we shall assume that the dominant dynamical mode to cause the observed cross-relaxation is the tumbling of water molecules in the bound state for which the correlation time can be evaluated by comparing the 17 O relaxation rates (Table 1) in the micellar sample and in bulk. Assuming N ϭ 6 ''bound'' water molecules, we obtain a correlation time c of about 4.5 ps, which is about 2.5 times the value found in bulk water at 45°C (7,28).…”

The effects of magnetic fields on water molecular hydrogen bonds

“…The proton spin-lattice relaxation time T 1 is approximately related to the viscosity g. The relationship [21] T 1 / T=g / expðÀE=RTÞ; ð10Þ with a common activation energy E is expected to hold provided the rotational and translational motions are controlled by a single kinetic process.…”

Rotational dynamics in supercooled water from nuclear spin relaxation and molecular simulations

“…25 These quadrupolar nuclides have been used extensively to study rotational dynamics in water, also in the supercooled regime. [26][27][28][29][30][31] In fact, no other experimental technique can provide information about water dynamics down to the practical limit of supercooling. On the other hand, because molecular rotation even in supercooled water (at ambient pressure) is fast compared to the highest accessible NMR frequencies, the nuclear spin relaxation rate only yields the time integral of the TCF, that is, the integral rotational correlation time.…”