Study of proton spin–lattice relaxation in the water–dioxan system

Abstract

Measurements have been made of the spin–lattice relaxation times of the proton-containing species in the systems water–dioxan, water–deuteriodioxan, and deuterium oxide–dioxan. Analysis of the contribution of dioxan to the relaxation rate of water and vice versa suggests that at low dioxan concentrations closer contact can occur between the different species than can occur between water molecules. This is probably due to the lack of ability of the dioxan protons to form hydrogen bonds, and it is suggested that as a consequence of this the structure of the water surrounding a dioxan molecule is stabilised, and may form a ‘cage’ which encloses the dioxan molecule, but which does not form intermolecular bonds with it. Supporting this idea, the rotational correlation time of dioxan was found to be independent of concentration up to X ca. 0·2 (X= mole fraction of dioxan), whereas that of water increased linearly in the same range. A change in the system occurs near X= 0·2 and it is suggested that this reflects the transformation of the system from one of dioxan dispersed in a matrix of water to one of clusters of water molecules dispersed in a matrix of dioxan.