Domain Analysis in Nanostructured Liquids: A Post-Molecular Dynamics Study at the Example of Ionic Liquids

In the present computational work, we develop a new tool for our trajectory analysis program TRAVIS to analyze the well-known behavior of liquids to separate into microphases. The dissection of the liquid into domains of different subsets, for example, in the case of fluorinated ionic liquids with anionic and cationic head groups (forming together the polar domain), fluorous, and alkyl subsets is followed by radical Voronoi tessellation. This leads to useful average quantities of the subset neighbor count, that is, the domain count that gives the amount of particular domains in the liquid, the domain volume and surface, as well as the isoperimetric quotient, which provides a measure of the deviation of the domains from a spherical shape. Thus, the newly implemented method allows analysis of the domains in terms of their numbers and shapes on a qualitative and also quantitative basis. It is a simple, direct, and automated analysis that does not need evaluation of the structure beforehand in terms of, for example, first solvent shell minima. In the microheterogeneous ionic liquids that we used as examples, the polar subsets always form a single domain in all investigated liquids. Although the fluorous side chains are also more or less connected in one or, maximally, two domains, the alkyl phases are dispersed.