a) b - École Polytechnique de Montréal

The harmonic mean equation approach is a classic approach for estimating the interfacial tension
of polymer pairs and has been used widely in a number of studies(Wu, 1982). It can be seen
that, compared to other polymer pairs, mixtures with PANI result in exceptionally high
interfacial tensions. It thus follows from spreading theory that PANI will not be driven to
encapsulate other polymers in a multi-component blend, rather it will tend to be encapsulated by
virtually every other polymer species. For example, in a ternary HDPE/PVDF/PANI blend, a
positive spreading coefficient value of 7.3 mN/m for λPVDF/PANI predicts encapsulation of PANI
by PVDF as confirmed in Figure 4-3b. In that figure, the voids left by the extracted PVDF can be
clearly seen to show that PVDF formed an interlayer between HDPE and PANI.
By increasing the number of components in a multi-percolated structure, the percolation
threshold of all phases sharply decreases. Thus, a unique approach to achieve a low percolation
threshold conductive PANI device would be to prepare a multiple percolated blend system with
PANI as the innermost phase. In this work we will examine the progressive morphological
development of highly continuous multi-component structures by first examining the
development of multi-encapsulated ternary to quinary droplets which are referred to here as
onion morphologies. Then, the required conditions for transformation of the onion morphology
to continuous multi-percolated morphologies and the conductivity of those systems are
examined.
4.4.2 Self-Assembled Onion Morphology and the Hierarchical Ordering of
Phases
Typically, in the literature, a core/shell morphology is used to describe a droplet comprised of
one phase encapsulated by another single phase. Here, we use the term onion morphology,
schematically shown in Figure 4-4, to describe a multi-phase, multi-encapsulated dispersed
droplet structure. In other words, a polymeric droplet phase comprised of layers of different
polymers assembled concentrically. Figure 4-4 shows schematically the progression from a
matrix-droplet(Figure 4-4a) to a core/shell(Figure 4-4b) and finally two cases of onion
morphology(Figures 4-4c and 4-4d).
110