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a) b - École Polytechnique de Montréal

a) b - École Polytechnique de Montréal

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CHAPTER 3 - ORGANIZATION OF THE ARTICLES<br />

To achieve the main objective of this work, an elegant technique to reduce the continuity<br />

and/or electrical percolation threshold of a conductive polymer is <strong>de</strong>veloped by increasing the<br />

number of continuous structures in polymer blends. Polyaniline and four other commercial<br />

polymers with specific surface tensions, polarity and interfacial tensions are precisely selected.<br />

The interfacial tensions between various components show a range from 1 mN/m for<br />

PVDF/PMMA to 26.9 mN/m for PANI/HDPE.<br />

Morphological sample characterization is performed by both SEM and FIB-AFM techniques.<br />

The polymer blends are prepared in a melt-blending process in an internal mixer at 50 rpm for 8<br />

min at 200°C. Selective solvent extraction of phases either assists in better <strong>de</strong>tection of phases in<br />

or<strong>de</strong>r to collect qualitative data, or is employed to produce porous samples. Combination of FIB<br />

treatment and AFM technique allows us to clearly distinguish the phases based on the<br />

topographical contrast formed by the difference in FIB etching rate of materials. In or<strong>de</strong>r to study<br />

the effect of viscosity ratio on the ternary blends, both low molecular weight and high molecular<br />

weight poly(methyl methacrylate) are selected. Fully interconnected porous materials are used as<br />

substrates for alternate <strong>de</strong>position of PSS and PANI.<br />

In the first step, three components, namely high <strong>de</strong>nsity polyethylene (HDPE), polystyrene<br />

(PS), and poly(methyl methacrylate) (PMMA), are carefully chosen to satisfy the<br />

thermodynamic conditions. The positive spreading coefficient of PS over PMMA predicts that<br />

the PS phase situates at the interface of the HDPE and PMMA phases, and a complete wetting<br />

case occurs. Experimental results confirms the prediction of the morphology by the spreading<br />

theory as the i<strong>de</strong>ntification of the phases can be clearly seen by the topographical heights<br />

induced by FIB etching and subsequently quantified by AFM analysis in the topographical mo<strong>de</strong>.<br />

Addition of fourth phase (PVDF) to the ternary blend with complete wetting of<br />

HDPE/PS/PMMA, provi<strong>de</strong>d that the entire set of thermodynamic spreading equations is<br />

satisfied, results in hierarchically or<strong>de</strong>red phases of HDPE|PS|PMMA|PVDF. The Harkins<br />

spreading theory predicts a hierarchically or<strong>de</strong>red structure of HDPE|PS|PMMA|PVDF|PANI by<br />

addition of PANI to a quaternary HDPE|PS|PMMA|PVDF blend. Experimental results show a<br />

very good consistency between these predictions and qualitative results.<br />

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