a) b - École Polytechnique de Montréal

y Harkins theory, PS will always situate at the interface. Thus, the coalescence of the PMMA
cores directly results in the coalescence of PS shells to each other. When the concentration of the
PMMA phase becomes high enough to create a continuous network throughout the sample, the
PS phase is forced to adopt a continuous form to spread over the PMMA phase(shown by
schematic and by micrograph in Figures 6-5c and 6-5d). FIB-AFM characterization of 40/20/40
HDPE/PS/PMMA blend reveals approximately such a morphology(Figure 6-5d). This is a tri-
continuous structure or double-percolated morphology and by definition all phases are highly
continuous.
Tri-continuous structures can be classified into two categories: type I and type II. The former is
shown in Figure 6-5c) and 6-5d), as described above. In that case the PS composition is low
enough such that most of the PS situates at the interface, apart from some minor droplet
formation in the PMMA. In the Type II case, as the concentration of PS is increased, more
isolated droplets are located in the PMMA since the HDPE/PS/PMMA interface is already
saturated by PS. These droplets coalesce into elongated structures as the concentration increases
until the PS within the PMMA also forms a fully continuous interconnected phase. Such a
structure is shown by micrograph and by schematic in Figures 6-5e) and 6-5f) Note that the
structure can be described as a co-continuous morphology of PS and PMMA separated by a PS
layer from a fully continuous HDPE phase. It should be noted that this morphology is still
consistent with Harkins theory as phase B still fully separates phases A and C. In Figure 6-5f) for
30/30/40 HDPE/PS/PMMA the voids left by the selective extraction of PS can be clearly seen to
show that PS forms an interlayer between HDPE and PMMA. A fully interpenetrated network of
PS and PMMA is also visible.
Hence, tri-continuous type I is transformed to tri-continuous type II by increasing the
concentration of the phase separating the other two phases.
6.4.3 Matrix/ Two Separate Dispersed Phases Morphology
Another type of sub-morphology in the complete wetting case of HDPE/PS/PMMA is the matrix
with two separate dispersed phases morphology(shown as a schematic in Figure 6-5g). In that
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