a) b - École Polytechnique de Montréal

The dispersed phase in a binary polymer blend can take the form of fibers, lamella and A-B-A
droplet-in-droplet type structures(Molau & Keskkula, 1966; Reignier & Favis, 2000). In an A/B
binary blend, the dispersed phase type structure(Figure 6-1b) is converted to a continuous type
structure through an increase in the composition. By increasing the concentration of dispersed
phase A, droplets coalesce resulting in a percolation threshold point being reached. This
percolation threshold is the first connected pathway in the blend(Figure 6-1a). Classic
percolation theory defines the percolation threshold as the onset of long-range connectivity in
random systems and it occurs at a volume fraction of 0.156 for a random mono-disperse
distribution of spheres(Scher & Zallen, 1970). Through a further increase of minor phase
concentration, levels of continuity increase until a fully-interconnected co-continuous
morphology is obtained(Figure 6-1c). Co-continuity is defined as the case where each phase is
fully continuous in the blend system. Since this often occurs over a concentration range for
binary polymer blends, this is also known as the region of dual-phase continuity. Phase inversion
is defined as the concentration point where co-continuity converts into a matrix/dispersed phase
morphology. It has been reported that the interfacial tension and the viscosity ratio can also
influence the position of the region of dual-phase continuity(Jordhamo, et al., 1986; Mekhilef &
Verhoogt, 1996).
Much less work has been carried out on the fundamental morphological states present in ternary
polymer blends comprised of significant quantities of 3 distinct phases. Recently, some papers
have described the morphological behavior of ternary systems with complex morphologies such
as A-B-C composite-droplet structures(Reignier & Favis, 2000; Reignier, et al., 2003) and
double-percolated morphology(Zhang, et al., 2007).
Complete wetting and partial wetting are two broad categories of morphological states
possible for ternary polymer blends. In an A/B/C system, complete wetting describes the case
where the most stable thermodynamic state is when one of the phases, say phase B, will always
position itself to completely separate phases A and C. In that case phases A and B completely
wet each other and phases B and C also completely wet each other. In the case of partial wetting,
the most stable thermodynamic state is when there is three-phase contact. In that case, for
example, droplets of B will situate at the A/C interface such that all three phases are in contact
with each other(Torza & Mason, 1970; Virgilio, Marc-Aurele, et al., 2009). Both complete and
partial wetting can be described by spreading theory as defined by Harkins equation. A
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