Methanol-water solutions: A bi-percolating liquid mixture

Abstract

An extensive series of neutron diffraction experiments and molecular dynamics simulations has shown that mixtures of methanol and water exhibit extended structures in solution despite the components being fully miscible in all proportions. Of particular interest is a concentration region (methanol mole fraction between 0.27 and 0.54) where both methanol and water appear to form separate, percolating networks. This is the concentration range where many transport properties and thermodynamic excess functions reach extremal values. The observed concentration dependence of several of these material properties of the solution may therefore have a structural origin.

Long-range specific ion-ion interactions in hydrogen-bonded liquid films

“…The failure of AN to propagate LR-SIE confirms our conjecture, but the experiments in IPA appear to contradict it. However, we consider that the latter result represents a false negative because IPA, in contrast with H 2 O and MeOH, [49][50][51][52][53][54][55][56] lacks an extensive H-bond network. Alkyl groups restrict the number of configurations amenable to hydrogen bonding, and this effect increases with the number and size of the alkyl groups surrounding O-H moieties.…”

Fluctuating micro-heterogeneity in water–tert-butyl alcohol mixtures and lambda-type divergence of the mean cluster size with phase transition-like multiple anomalies

“…However, this concept fell short in explaining the modern diffraction experiments [23][24][25][26][27]. The alternative picture proposed self-association of the amphiphilic solutes to form hydrophobic aggregates [22,28].…”

Microstructure of neat alcohols

“…Associated liquids, such as water and alcohols, for example, belong to a special class because of the particularity of the hydrogen bonding (HB) that is highly directional, and tend to enhance the structure the liquid locally. One particularly interesting example of this phenomena is the microheterogeneous nature of aqueous mixtures, which has attracted a recent upsurge of interest [1,2,3,4,5,6,7]. Perhaps the most remarkable reported fact is that watermethanol mixtures show local immiscibility at microscopic level, while being miscible at macroscopic level [1,2].…”

“…From a statistical mechanical point of view, homogeneity is expressed by the fact that the order parameter, in this case the one body density, which formally depends on both the position and orientation of a single particle 1 (as in a crystal or a liquid crystal, for example), is a constant throughout the sample: ρ (1) (1) = ρ = N/V , where N is the number of particles per volume V. As a consequence, the microscopic description of the structure of a neat liquid starts from the two-body density function ρ (2) (1, 2) = ρ (1) (1)ρ (1) (2)g(1, 2) that expresses the density correlations between particles 1 and 2, and reduces in this case to ρ 2 g(1, 2) , where g(1, 2) is the pair distribution function. Associated liquids, such as water and alcohols, for example, belong to a special class because of the particularity of the hydrogen bonding (HB) that is highly directional, and tend to enhance the structure the liquid locally.…”

“…One particularly interesting example of this phenomena is the microheterogeneous nature of aqueous mixtures, which has attracted a recent upsurge of interest [1,2,3,4,5,6,7]. Perhaps the most remarkable reported fact is that watermethanol mixtures show local immiscibility at microscopic level, while being miscible at macroscopic level [1,2]. In order to appreciate this result it is interesting to compare it to microemulsions where bicontinuous phases are usually observed, and micro-immiscibility operates with domain sizes ranging from 100 nanometers to few micrometers, while those mentioned here are around few nanometers-that is about few molecular diameters.…”