Wünsch, M., Wolf, B. A.

"Interfacial Tension Between Coexisting Polymer Solutions in Mixed Solvents and Its Correlation With Bulk Thermodynamics: Phase Equilibria (Liquid/Gas and Liquid/Liquid) for the System Toluene/Ethanol/Pdms"

*Polymer* **2002, ** *18, 43*, 5027-5034.

**Abstract: **Vapor pressures, phase equilibria and interfacial
tensions sigma were measured for solutions of poly(dimethylsiloxane) (PDMS, M-w =
75 kg/mol and M. = 50 kg/mol) in mixed solvents of toluene (TL) and ethanol (EtOH)
at 30, 40, 50 and 60 degreesC. The experimental ternary phase diagrams can be
modeled quantitatively from the determined concentration and temperature dependent
binary interaction parameters chi(ij) if the experimentally inaccessible composition
dependence o chi(EtOH)/(PDMS) is adjusted. The relations between o, and the
equation of state of the system differ from that applying to single solvents.
The exponents as well as the amplitude prefactors of the corresponding scaling
laws (e.g. the dependencies of o, on the length of the tie lines or on the hump
energy, i.e. on the intrusion into the two phase regime quantified in terms of
Gibbs energies) change considerably with temperature. However, this variation
can be reduced significantly by normalizing the independent variables. Dividing
the length of the tie lines by the length for the corresponding binary
subsystem proves more efficient than the distance of these tie lines
from the critical point of the ternary system relative to the maximum
distance of the binary subsystem. A combined normalization does not
improve the situation. (C) 2002 Elsevier Science Ltd. All rights reserved.

preprint number: 228