a) b - École Polytechnique de Montréal

a) b)
c) d)
e) f) g) h)
Figure 5-5. Scanning electron microscope images of the morphologies of the porous structures
showing the influence of annealing. The top row is without annealing, the bottom row is after
annealing. All components have been extracted except HDPE. a),e) Sample (A); b),f) Sample
(B); c),g) Sample (C); and d),h) Sample (D).
Double percolated HDPE/PS/PVDF and HDPE/PMMA/PVDF blends and triple-percolated
HDPE/PS/PMMA/PVDF were subjected to quiescent annealing for 15 minutes in a compression
molding press at very low contact pressures. This operation results in a substantial increase in the
average phase size. Figure 5-5 shows the morphology of the blends after annealing and
subsequent extraction of all phases except for HDPE. The phase size increase is dramatic and is
shown for sample B to increase from approximately 40μm to 500μm as exhibited
morphologically in Figures 5-5b and 5-5c. The phase increase before and after annealing for the
other samples A, C, and D is also substantial and ranges from 5 to 15 times (Figure 5-5). The
results indicate that the coalescence of a multi-percolated system occurs much faster than
coalescence in a binary blend. Yuan et al.(Zhenhua Yuan, 2005) reported that, in the best case
scenario, a binary blend requires approximately 40 minutes to coarsen from several microns to a
phase size of about 160 microns. Consequently, the required annealing time to achieve 400-500
microns is estimated at about two hours of annealing. It is proposed that geometrical restrictions
in a multi-percolated system enormously accelerate coalescence effects while still maintaining
full continuity of all components.
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