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a) b - École Polytechnique de Montréal

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CHAPTER 7 - GENERAL DISCUSSIONS AND PERSPECTIVE<br />

In the previous chapters, it was shown that a hierarchically or<strong>de</strong>red, interfacial tension driven<br />

morphology can be assembled. In this multiple-percolated structure, thermodynamic properties<br />

can <strong>de</strong>termine the number of interfaces between phases(the number of contacts between phases).<br />

In the next perspective of the work the influence of viscous forces on the morphology by<br />

changing the shape and size of the phases can be studied. For example, by increasing the shear<br />

stress in a bi-continuous/dispersed phase morphology, the size of the droplets should be<br />

<strong>de</strong>creased due to the increasing breakup rate as compared to coalescence. Moreover, due to the<br />

higher shear force, the shape of the droplets may also become more elongated. Therefore,<br />

changing the applied shear stress on the system would be expected to result mostly in the<br />

variation of the size and shape of the phases. Changing the hierarchical or<strong>de</strong>r of phases in the<br />

blend, which <strong>de</strong>pends significantly on the thermodynamic properties of the system, is almost<br />

impossible. It is well-known that the third factor affecting the morphology of multi-component<br />

blends is the composition of phases. This factor affects the morphology by imposing a<br />

geometrical restriction between phases and controls the rate of breakup and coalescence. At high<br />

concentration of one phase the droplets of that phase coalesce further with each other and<br />

therefore the rate of coalescence increases until a continuous structure is constructed. For blends<br />

comprised of more than three components, composition can also play a role in the prediction of<br />

the phase morphology. Thermodynamics plays another role in the morphology of ternary blends<br />

through the governing Harkins equation and the prediction of three-phase contact and two-phase<br />

contact morphologies as mentioned in <strong>de</strong>tail in chapter 6. In both cases of complete and partial<br />

wetting, a high interfacial tension between phases results in a <strong>de</strong>crease of the interfacial area<br />

between them leading to larger phase sizes. All the effects of these three<br />

parameters(composition, interfacial tension, and shear stress) are schematically shown for a<br />

complete wetting case of a ternary blend in Figures 7-1 and 7-2. Figures 7-1 and 7-2 illustrate<br />

various morphologies of a blend with a matrix of phase (A) <strong>de</strong>pending on the interfacial tension<br />

of B/C and the composition of phases B and C at low shear rate and high shear rate, respectively.<br />

It is shown that at low concentration of minor phases, a matrix/core-shell morphology is<br />

observed. At higher concentration of minor phases, tri-continuous and bi-continuous/dispersed<br />

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