Electric Response and Conductivity Mechanism of Blended Polyvinylidene Fluoride/Nafion Electrospun Nanofibers

摘要

The electrical relaxation and polarization phenomena of electrospun PVDF (P)/Nafion (N) blended fiber mats ([P/N_(0.9)]~M and β-[P]~M) and membranes ([P/ N_(0.9)]~(MM)) are compared with those of the solvent-cast membrane of identical composition ([N]~C and [P/N_(0.9)]~C). The nature of the interactions between the two blended polymer components, that plays a pivotal role in the electrical nature of the resulting materials, is found to be governed by the fabrication method, with those materials obtained via electrospinning undergoing a "reciprocal templating" phenomenon that renders their electrical behavior (especially when in the dry state) significantly different from that of the blended membrane obtained via solvent casting. Broadband Electrical Spectroscopy (BES) demonstrates that the electric response of the blended materials is modulated by polarization phenomena and by α, β, and y dielectric relaxation events of Nafion domains supported on β-PVDF. The coupling between the relaxations of β-PVDF with those of Nafion matrix is directly correlated to the "reciprocal templating effect, which modulates the interactions between Nafion and PVDF in electrospun membranes. Two types of conductivity mechanisms characterize the H~+ migration within the polymer blends: (1) interdomain H~+ migration events by "charge-exchange" phenomena along percolation pathways and (2) H~+ exchange between delocalization bodies (DBs) at binding sites at the interface between domains with different ε, size, and morphology. The electrical response of the electrospun membranes also suggests that they do not comprise water clusters with a large size such as those typically observed in pristine Nafion. Rather, the adsorbed H_2O molecules, under wet conditions, form thin solvation shells wrapping the polar side chains of the Nafion component. At T = 80 ℃, the conductivity of the studied materials decreases in the order [N]~C (0.043 S·cm~(-1)) ≈ [P/N_(0.9)]~C (0.042 S·cm~(-1)) > [P/N_(0.9)]~M (0.031 S·cm~(-1)) > [P/N_(0.9)]~(MM) (0.011 S·cm~(-1)).