a) b - École Polytechnique de Montréal

Addition of a low concentration of HDPE to the system leads to the encapsulation of HDPE
droplets in a highly continuous PS network resulting in a bi-continuous/dispersed phase
morphology and a slight reduction of PS continuity(point b in Figure 6-11). A further increase of
HDPE phase generates a tri-continuous morphology(type II) where the coalescence of HDPE
droplets forms a continuous phase of HDPE in highly continuous PS (point c in Figure 6-11).
Note that at point c for the 30/30/40 HDPE/PS/PMMA blend, the continuity level of PS is
lowered to 68% Such a decrease in the continuity level is attributed to the entrapment of some
parts of the PS phase in the PMMA network. Point d indicates the expected drop in continuity
after the formation of the type I tricontinuous structure at point e. At point e, the 82% HDPE
volume fraction corresponds to the 50/10/40 HDPE/PS/PMMA blend. This type I tri-continuous
structure with a PS continuity of 76% represents the case where 50% HDPE and 40% PMMA
form a co-continuous structure with a thin PS layer situated at the HDPE/PMMA interface.
Finally, replacing all the PS with HDPE results in a (60%HDPE matrix/40%PMMA dispersed
phase) blend (point f in Figure 6-11).
Local maximum continuity of 78% is obtained for 48/12/40 HDPE/PS/PMMA blend from Figure
6-11. The most important observation for scheme a, where the PMMA concentration is held at
40%, is that due to the thermodynamic limitations of spreading, the system is never able to form
PS droplets even at a very low concentration of PS. PS always spreads between HDPE and
PMMA in order to separate those two components. Thus even the smallest amount of PS in
scheme a) presents a layer structure as opposed to droplets.
In scheme (b), from Figure 6-10, the concentration of the PS phase is kept constant at 10%
volume fraction and the concentration ratio of the two other phases changes. In Figure 6-12, the
continuity of the PS phase following Scheme b is examined as a function of the % concentration
of HDPE in (HDPE plus PMMA) where HDPE plus PMMA always equals 90% in the ternary
blend with PMMA. Thus, 100% HDPE refers to the 90%HDPE/10%PS blend, while 50% HDPE
in Figure 6-12 refers to the 45%HDPE/10%PS/45%PMMA blend. This scheme allows for the
study of the effect of the composition of the inner phase(HDPE) and the outer phase(PMMA)
on the morphology of the middle phase(PS). It is interesting to note that in this case, the PS
continuity curve is almost symmetric. At 0% HDPE, the continuity of PS is zero due to the
presence of PS droplets within the matrix of PMMA(point a in Figure 6-12).
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