a) b - École Polytechnique de Montréal

Three examples are shown in Figure 6-14: 50/40/10 HDPE/PS/PMMA, 10/30/60
HDPE/PS/PMMA, and 50/25/25 HDPE/PS/PMMA. PMMA has a much lower viscosity than PS
which has a lower viscosity than HDPE. Also, the PS/PMMA interfacial tension is much lower
than the PS/HDPE or PMMA/HDPE one (see Table 6-2). In the case of 50/40/10
HDPE/PS/PMMA(Figure 6-14a), the PMMA phase is at a low concentration (10%), low
PMMA/PS viscosity ratio and a low PMMA/PS interfacial tension (see Tables 6-1 and 6-2). It
can be seen that the PMMA is distributed in the PS phase as numerous small PMMA droplets
leading to high interfacial area between PS/PMMA. In that same sample, PS and HDPE form a
co-continuous structure. The FIB/AFM micrographs allow for a clear identification of the small
PMMA droplet phases in the PS. The topographical heights following the trace line show the
short interval between PS and PMMA phases and the long interval for the HDPE phase. In the
ternary 50/25/25 HDPE/PS/PMMA blend, the increased concentration of PMMA results in the
coalescence of PMMA droplets resulting in the formation of large PMMA droplets. In the case
of the ternary blend comprised of 10/30/60 HDPE/PS/PMMA large droplets of HDPE are
observed in the PS phase while PS and PMMA comprise a co-continuous structure(Figure 6-
14c). These results are consistent with the low viscosity ratio and interfacial tension of
PS/PMMA and high viscosity ratio and interfacial tension of HDPE/PS.
6.5 Conclusions
Complete wetting in a ternary polymer blend is an interfacial tension driven state where one of
the components will always tend to completely separate the other two. It occurs when one of the
three possible binary spreading coefficients in the system has a positive value, as defined by
Harkins spreading theory. This work examines the complete range of morphological states
possible for such a system over the entire ternary composition diagram as prepared by melt
mixing. High-density polyethylene(HDPE), polystyrene(PS), and poly(methyl
methacrylate)(PMMA) are selected as a model system showing a positive spreading coefficient
of PS over PMMA, thus in all cases the PS phase separates HDPE and PMMA. Four subcategories
of morphologies can be identified, depending on the composition of phases, including:
a) matrix/core-shell dispersed phase; b) tri-continuous; c) bi-continuous/dispersed phase;, and d)
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