Site-site memory equation approach in study of density/pressure dependence of translational diffusion coefficient and rotational relaxation time of polar molecular solutions: Acetonitrile in water, methanol in water, and methanol in acetonitrile

Abstract

We present results of the theoretical study and numerical calculation of the dynamics of molecular liquids based on the combination of the memory equation formalism and the reference interaction site model (RISM). Memory equations for the site-site intermediate scattering functions are studied in the mode-coupling approximation for the first-order memory kernels, while equilibrium properties such as site-site static structure factors are deduced from RISM. The results include the temperature-density (pressure) dependence of translational diffusion coefficients D and orientational relaxation times tau for acetonitrile in water, methanol in water, and methanol in acetonitrile--all in the limit of infinite dilution. Calculations are performed over the range of temperatures and densities employing the extended simple point charge model for water and optimized site-site potentials for acetonitrile and methanol. The theory is able to reproduce qualitatively all main features of temperature and density dependences of D and tau observed in real and computer experiments. In particular, anomalous behavior, i.e, the increase in mobility with density, is observed for D and tau of methanol in water, while acetonitrile in water and methanol in acetonitrile do not show deviations from the ordinary behavior. The variety exhibited by the different solute-solvent systems in the density dependence of the mobility is interpreted in terms of the two competing origins of friction, which interplay with each other as density increases: the collisional and dielectric frictions which, respectively, increase and decrease with increasing density.

Thermodynamic dependences of slip length for nanofluidic flows over crystalline surfaces: Predictions of molecular theory of solvation

“…Further to all thermodynamic data for water in wide range of temperatures and pressures [36], molecular theory of solvation [27] equips us with the detailed knowledge about the pressure and/or temperature induced microscopic structural changes in neat water [20,21], aqueous solutions of acetonitrile and methanol [22][23][24], and tert-butyl alcohol [37]. Having that, we could not resist the temptation to check if the hydrogen bond network formation and rupture would also be responsible for such outrageous values of the slip length for water.…”

“…19, the friction coefficient is inversely proportional to viscosity, so that its tremendous decrease automatically assumes an increase of friction between the solid surface and the liquid. Another and rather little contribution to ξ w,ab comes from the fact that in compression, when hydrogen bonds are ruptured, first peak of radial distribution function for oxygen sites becomes enhanced and for hydrogen sites substantially diminished [20][21][22][23][24]. We know [19] that in case of water principal contribution to the integral (3) comes from the first solvation shell of the oxygen site, while the same contribution from the hydrogen site is negligibly small.…”

“…Another type of anomalous behavior of water and aqueous solutions of acetonitrile and methanol we studied previously can be found in Refs. [20][21][22][23][24], where we describe the anomalous pressure and temperature dependence of their molecular mobility and orientational relaxation time. In Ref.…”

Pressure and temperature dependence on the hydrogen bonding and dynamics of ammonium ion in liquid water: A molecular dynamics simulations study

“…Theoretically, Hirata and co-workers have calculated the dynamics of ions in water and other polar liquids from the molecular theory [24][25][26] based on the interaction-site model for molecular liquids and on the generalized Langevin equation combined with the mode-coupling theory. They have also provided a quantitative explanation of the pressure dependence of diffusion coefficient and orientational relaxation time of different solutes in water and some other solvents [27]. Recently, Chowdhuri and co-worker [28] have studied the importance of solvents of hydrogen bonding network on the dynamics of ions in liquid methanol and water under pressure, at 258 and 298 K. It is observed that the hydrogen-bond lifetime and structural-relaxation time of methanol are increasing monotonically with pressure and the results are more prominent at low temperatures, whereas in the case of water, an opposite trend of the hydrogen bond dynamics is observed under similar conditions.…”

Rotation of Four Small Nitroxide Probes in Supercooled Bulk Water

“…The dielectric friction is produced by the inhomogeneity in the charge density of water, caused by the density fluctuation due to the hydrogen bond. 51 In other words, the BC becomes less slip, so the hydrodynamic radius appears larger, Figure 4.…”