a) b - École Polytechnique de Montréal

When PS is the matrix with PMMA and HDPE minor phases, separate dispersions of HDPE and
PMMA have the lowest interfacial free energy (Figure 2-11b). Finally, when PMMA is the major
phase and PS and PMMA are minor components, the HDPE is encapsulated in the PS phase
(Figure 2-11c).
2.1.2.2.4 Interfacially Modified Ternary Polymer Blends
As mentioned above, the Harkins theory can predict whether the morphology of a ternary blend
is complete wetting or partial wetting. This theory is based on the interfacial tension of polymer
pairs. Hence, by changing the interfacial tension between two polymers via addition of
interfacial modifier, the prediction of the morphology by Harkins can toggle between the
complete wetting case and the partial wetting case. Another effect of interfacial modifier is that
in a partial wetting case, one phase moves from one phase to the other phase, thus creating more
interfacial area. Guo et al. (Guo, Packirisamy, et al., 1997) showed that in a ternary polymer
blend of 70/10/20 HDPE/PS/PP, all three phases have interface with each other (Figure 2-12a).
This is predicted by the Harkins equation, as interfacial tension values of γPE/PS=5.9 mN/m,
γPE/PP=1.1 mN/m, and γPP/PS=5.1 mN/m show three negative spreading coefficients. A blend
without interfacial modifier represents more interfacial area between the PS phase and the PP
phase (Figure 2-12a). Addition of 0.5% PS/PE diblock copolymer shows movement of the major
part of the PS phases to HDPE (complete wetting case), and also more PS droplets at the
interface move to the HDPE phase (Figure 2-12b).
The other effect of interfacial modifier on the blend, as previously discussed, is increasing
interfacial area between phases. Therefore, addition of diblock copolymer to the blend results in
a decrease of the droplet size. Figure 2-12c shows that addition of 2% PS/PE copolymer to
70/10/20 HDPE/PS/PP results in smaller droplet sizes in both the partial and complete wetting
cases.
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