Chemistry Reference
In-Depth Information
0
-10
-20
-30
0.0
-20.0
-40.0
-60.0
-80.0
-100.0
0.0
0.1
0.2
0.3
0.4
0.5
0.6
Reduced Bulk Density
FIGURE 8.4
Solvent density dependence of
V
2
∞
(SR) and
H
r
,∞
(SR) for the attractive Lennard-
Jones pyrene (2)/CO
2
(1) system along the near-critical reduced isotherm
T
r
= 1.02. All quanti-
ties are made dimensionless using the solvent's Lennard-Jones parameters from Table 8.1.
regression purposes, for example, to estimate accurate values of
V
2
∞
at other supercrit-
ical state conditions (Gruszkiewicz and Wood 1997) based only on the corresponding
water properties, but it also suggested some relevant questions regarding the micro-
scopic mechanism underlying such a behavior for
D
21
(
T
,ρ).
To gain insights into the observed behavior of
D
21
(
T
,ρ), we carried out integral
equation (IE) calculations on model systems defined as charged hard-sphere ions
immersed in an aqueous-like solvent, described as hard spheres with embedded
point polarizabilities and permanent electrostatic multipole moments including
quadrupole and octupoles, by solving the reference hypernetted-chain (RHNC)
equations with solvent polarization effects treated at the self-consistent mean-
field (SCMF) level (Chialvo and Cummings 1994, 1999; Chialvo et al. 2000c). In
Figure 8.10, we display the IE-predicted solvent density dependence of
D
21
(
T
,ρ)
along three supercritical isotherms for infinitely dilute CsBr aqueous-like solu-
tions (Chialvo et al. 2001), in comparison with the corresponding experimental
data from Sedlbauer, Yezdimer, and Wood (1998) within the temperature and
density ranges 604 < T(K) < 717 and 0.26 < ρ (g/ cm
3
) < 0.60, respectively. The
outstanding feature of the IE results is their lack of temperature dependence for
supercritical densities, that is,
D
21
(
T
,ρ) ≅
D
21
(ρ ≥ ρ
c
), a behavior that mirrors the
experimental observations in other supercritical aqueous electrolyte and nonelec-
trolyte systems (O'Connell, Sharygin, and Wood 1996; Gruszkiewicz and Wood
1997; Sedlbauer, Yezdimer, and Wood 1998).
