Chemistry Reference
In-Depth Information
r
or
R
(Å)
0
20
40
60
1.2
1.1
1
0.9
6000
4000
2000
0
4
200
2
0
100
0
2
4
6
0
0
0.2
0.4
0.6
0.8
1
k
(1/Å)
FIGURE 7.12
Illustration of the TS approach for molecular emulsions. Top panel shows a
close-up of the water-water RDF at large distances, with red curve being the initial data from
MD, gold curve is the abrupt continuation and green curve the TS continuation. Middle panel
shows the corresponding RKBIs as a function of integration distance, and the lower panel the
structure factor with a visible domain prepeak.
(See color insert.)
7.4 CONCLUSIONS
In their introduction to nonionic aqueous mixtures, Rowlinson and Swinton state
in their topic on mixtures that these systems would require more insight than other
types of mixtures (Rowlinson and Swinton 1982). In the early days of the develop-
ments of the theory of liquids, De Gennes reminded us that according to Landau,
the great Soviet physicist, such a theory could not exist nor be useful (De Gennes
1977). Decades later, these two statements seem very much valid since the theory of
aqueous mixtures is still full of mysteries and the corresponding theory of liquids
is still in infancy. The microheterogeneity in aqueous mixtures seems a good place
to understand liquids in a deeper way. Other challenges, such as understanding the
role of water in biological systems, are appealing (Wiggins 2008), but we first need
to understand aqueous mixtures.
The principal aim of this chapter was to show that complex liquid mixtures are
characterized both by fluctuations and intrinsic microheterogeneity; the latter arises
from the natural tendency of these systems to show microsegregated domains. These
domains are not to be confused with large concentration fluctuations, such as those
arising from phase-separating systems. The Kirkwood-Buff theory shows how the for-
malism of the statistical theory of liquids can be used to relate the integral of the
