Inhomogeneity of Mixing in Acetonitrile Aqueous Solution Studied by Small-Angle X-ray Scattering

Abstract

Acetonitrile aqueous solution has an upper critical solution temperature (UCST) at 272 K at c ) 0.38 (c represents the mole fraction of acetonitrile). To study quantitatively how the mixing scheme of the solution changes as a function of concentration and temperature, the concentration fluctuation, the Kirkwood-Buff parameters, and individual density fluctuations for acetonitrile and water were obtained by means of smallangle X-ray scattering experiments at 273, 279, and 298 K in the range of 0.0 e c e 0.5. The values of concentration fluctuation became larger close to UCST and exhibit a maximum at c ) 0.38. The mixing scheme of acetonitrile aqueous solution is discussed from the point of view of inhomogeneity of molecular distribution.

Ab initio study of the structural properties of acetonitrile–water mixtures

“…Lastly, the x AN = 0.5 mixture is in a special regime which large clusters of water and AN are separately formed exhibiting the microheterogeneous characteristics. This agrees well with the experimental studies [9,16,55,58,59]. One should note that the unit cell side length of the x AN = 0.5 simulation was 15.452 Å.…”

X-ray Raman scattering provides evidence for interfacial acetonitrile-water dipole interactions in aqueous solutions

“…5 The mechanism of inhomogeneous mixing in the MeCN-water binary system can be understood through a variety of interactions with different strengths and origin in the mixture. 6 MeCN molecules aggregate through dipole-dipole interactions while water molecules form hydrogen bonds (H-bonds) among each other. In aqueous solution two different types of interacting configurations between water and MeCN have been proposed where the OH axis of water and the CN axis of MeCN are either in-line, forming a H-bond between the hydrogen and the nitrile nitrogen, or in side-by-side antidipole arrangement with the CN bond parallel to the plane of the water molecule.…”

NMR study of heterogeneity in pyridine-N-oxide...HCl crystal

“…Some features of NMR spectra were processed using the Microcal Origin program package. [13], [14]. It is also known, that an ionic solute in systems exhibiting this phenomenon acts as increasing pressure [15], [16] which shifts the phase separation point towards higher temperatures.…”