Interfacial Tension in Binary Polymer Blends and the Effects of Copolymers as Emulsifying Agents - Polymer Thermodynamics - page 220

3.0

2.5

2.0

1.5

1.0

0.5

0.0

0 1000 2000 3000

Mn

4000 5000 6000

Fig. 16 Comparison of experimental interfacial tension for PDMS/PBD 1000 at 25 C[ 20 ]
with the theory of Ermonskin Semenov [ 33 ]. The interaction parameter a = w / u was adjusted to
3.35 10 3 mol/cm 3 ( u is the effective monomer volume)

interaction parameter w emerged. It was shown again that the relationship correlat-
ing w to the Hildebrand solubility parameter ( 44 ) was not suitable for evaluating the
theoretical predictions. The theoretical interfacial tensions of Broseta et al. [ 31 ]or
Helfand et al. [ 30 ] were found to increase with increasing temperature, which is
opposite to the behavior of the experimental interfacial tension data; this discrep-
ancy was also observed earlier [ 19 ]. Alternatively, the interaction parameter was
expressed as a sum of an enthalphic and an entropic contribution, w ¼ w H /T + w S ,as
suggested earlier by Anastasiadis [ 19 ]. The two coefficients were evaluated by
fitting the interfacial tension data at two different temperatures to the expression of
Broseta (83); these coefficients were then used to predict the interfacial tension for
other temperatures and different molecular weights with moderate success. Finally,
the theoretical predictions on the effects of molecular weight polydispersity on
interfacial tension [ 31 ] are in qualitative agreement with the data.
Lee and Jo [ 34 ] proposed a square-gradient theory combined with the Flory
Orwoll Vrij equation of state theory [ 248 ]. The theory was used to calculate the
interfacial tension between PS and PBD, and between PS and PMMA. For
the PS/PBD system, they utilized an experimental cloud point curve to determine