a) b - École Polytechnique de Montréal

Figure 5-3 illustrates a comparison between binary co-continuous structures (single percolated)
and a ternary one (double percolated) and shows that continuous phases can be generated at
lower concentrations of each phase in the latter case due to the lower percolation threshold of
those phases.
In Figure 5-3a, it is shown that a double percolated HDPE/PMMA/PVDF blend, after PMMA
and PVDF extraction, can result in a porous substrate of 33% HDPE which demonstrates a
homogeneous, perfectly interconnected structure while a binary blend of 33% HDPE and 67%
PVDF yields an imperfect continuous structure of HDPE (Figure 5-3b). Extraction experiments
indicate that 98% of the PMMA and PVDF were extracted in the ternary blend proving their high
levels of continuity. In the case of the 33%HDPE/67%PVDF binary blend, extraction of PVDF
resulted in a value of 108% of material indicating a significant quantity of HDPE present as
dispersed entities within the PVDF. The fully continuous binary 50% HDPE/50% PVDF blend is
also shown for comparison (Figure 5-3c). Clearly, a double-percolated morphology is a route
towards fully continuous phases at low phase concentrations. The subsequent extraction of
PMMA and PVDF leaves behind a fully interconnected porous HDPE substrate of low surface
area. In this work, as HDPE substrates were exposed to polyelectrolyte solutions, extra-large
pores also facilitated the penetration of the solution inward to the interconnected porous area.
The addition of a fourth component to form a quaternary blend with a triple-percolated
morphology between adjacent phases is also possible providing that the spreading coefficients of
the fourth phase and the engulfed phases satisfy Harkins equations. A more detailed study of the
generation of such structures is presented in a separate paper(Ravati & Favis, 2010). A triplepercolated
morphology is particularly interesting in the present work since it provides a route
towards the generation of porous channels of highly uniform size distribution. Figure 5-4
demonstrates such a structure in which PMMA situates at the interface of PS and PVDF in an
HDPE matrix. Thus this triple-percolated morphology follows the order
HDPE/PS/PMMA/PVDF (Figures 5-4a and 5-4b). Figures 5-4a and 5-4b represent quaternary
blends with the PMMA phase extracted, yielding PS layers engulfed in an HDPE matrix while
the PVDF phase remains at the core encapsulated by extracted PMMA. The removal of the PS
phase separates HDPE/PS/PMMA/PVDF into two parts: the HDPE matrix and PMMA/PVDF
core (Figure 5-4c). These figures unambiguously show that the PS and PMMA phases are
situated between HDPE and PVDF, and a hierarchical structure of four different phases is
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