Camel back shaped Kirkwood-Buff integrals

Some binary mixtures, such as specific alcohol-alkane mixtures or even water-tbutanol, exhibit two humps camel back shaped Kirkwood-Buff integrals (KBIs). This is in sharp contrast with the usual KBIs of binary mixtures having a single extremum. This extremum is interpreted as the region of maximum concentration fluctuations, usually occurs in binary mixtures presenting appreciable micro-segregation, and corresponds to where the mixture exhibits a percolation of the two species domains. In this paper, it is shown that two extrema occur in binary mixtures when one species forms meta-particle aggregates, the latter acts as a meta-species, and they have their own concentration fluctuations, hence their own KBI extremum. This meta-extremum occurs at a low concentration of the aggregate-forming species (such as alcohol in alkane) and is independent of the other usual extremum observed at mid-volume fraction occupancy. These systems are a good illustration of the concept of the duality between concentration fluctuations and micro-segregation. Published under an exclusive license by AIP Publishing.

Automated summary

Some binary mixtures exhibit a camel back shaped Kirkwood-Buff integral with two humps, which is in contrast to the usual single extremum. This occurs when one species forms meta-particle aggregates, resulting in their own concentration fluctuations and integral extremum.