| Abstract
| - The type of counterion present in the Nafion component of a blend with poly(vinylidenefluoride) (PVDF) is shown to affect phase separation and the crystalline polymorphism of the PVDFcomponent. Nafion neutralized with an alkali metal counterion, Na+, results in blends displaying large-scale phase separation upon heating to temperatures above the melting point of PVDF. In contrast, whenthe Nafion counterion is changed to a larger tetrabutylammonium counterion (TBA+), the melt ishomogeneous, and with the exception of the PVDF crystallites, large-scale phase separation is not observedafter the blend is cooled to room temperature. For the blends containing Na+-form Nafion, the crystallinemorphology of the PVDF component develops in predominately the α crystal form, similar to pure PVDFcrystallized from the melt. However, for blends containing TBA+-form Nafion, the PVDF componentcrystallizes with a higher content of the β- and/or γ-crystal forms. This effect of counterion type on thephase separation behavior and crystal morphology is attributed to the strength of the electrostatic cross-links within the Nafion component. Strong electrostatic cross-links induce gelation of the Nafion componentleading to phase separation at elevated temperatures, whereas weak electrostatic cross-links provide afree-flowing melt that allows for a more favorable mixing with the PVDF component and is thus capableof influencing the crystallization process.
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