Molecular understanding of the viscosity variety within self-assembled hydroxyl liquids

Abstract

The paper shows how molecular self-organization within supramolecular ensembles, spontaneously formed by hydroxyl molecules, reveals in the viscosity of liquids composed of such molecules. The problem is illustrated with differently hydroxy-substituted propanes, the molecules of which form supramolecular polymers of a great diversity, although they all can be named as “chain-like”. Molecules of 1-propanol form the “wire-like” (1-D) chains which practically do not affect the viscosity of the liquid. In propanediol, the “ribbon-like” (2-D) chains are formed, causing the viscosity increase by more than one order of magnitude. Finally, an addition of the third OH group to the diol molecules leads to an increase of the viscosity of formed 1,2,3-propanetriol (glycerol) by another almost two orders of magnitude. For significantly viscous glycerol we propose a model of supramolecular polymers, in which the ribbon-type chains are additionally linked to each other by perpendicular O-H⋯O hydrogen bonds, forming in that way 3-D network.