  The recently developed Perturbed-Chain Statistical Associating Fluid Theory
(PC-SAFT) is investigated for a wide range of model parameters including the
parameter m representing the chain length and the thermodynamic temperature T
and pressure p. This approach is based upon the first-order thermodynamic
perturbation theory for chain molecules developed by Wertheim and Chapman et
al. and includes dispersion interactions via the second-order perturbation
theory of Barker and Henderson. We systematically study a hierarchy of models
which are based on the PC-SAFT approach using analytical model calculations and
Monte Carlo simulations. For one-component systems we find that the analytical
model in contrast to the simulation results exhibits two phase-separation
regions in addition to the common gas-liquid coexistence region: One phase
separation occurs at high density and low temperature. The second demixing
takes place at low density and high temperature where usually the ideal gas
phase is expected in the phase diagram. These phenomena, which are referred to
as "liquid-liquid" and "gas-gas" equilibria, give rise to multiple critical
points in one-component systems, as well as to critical end points (CEP) and
equilibria of three fluid phases, which can usually be found in multicomponent
mixtures only. Furthermore, it is shown that the "liquid-liquid" demixing in
this model is not a consequence of a "softened" repulsive interaction as
assumed in the theoretical derivation of the model. Experimental data for the
melt density of polybutadiene with molecular mass Mw=45000g/mol are correlated
here using the PC-SAFT equation. It is shown that the discrepancies in modeling
the polymer density at ambient temperature and high pressure can be traced back
to ...
