Fast proton conduction in hydrogen bonded microheterogeneous systems:Bis(2-ethylhexyl)phosphoric acid/N-methyl formamide liquid mixtures

Structural and dynamical properties of bis(2-ethylhexyl)phosphoric acid (HDEHP)/N-methyl formamide(NMF) liquid mixtures in the whole composition range have been investigated by Fourier TransformInfrared spectroscopy (FT-IR), X-rays Diffraction (XRD), and AC complex impedance spectroscopy. Drivenby hydrogen bond interactions among HDEHP PO4H group and NMF CO and NH groups, and also by stericeffects among the HDEHP alkyl chains, the system microstructure is mainly characterized by the coexistenceof spatially separated hydrophilic and hydrophobic nanodomains showing local organization andshort-range order. The evolution of this structural feature with system composition has been highlightedby FT-IR and XRD. On the other hand, the thermally activated proton mobility within these hydrophilicdomains, as pointed out by AC complex impedance measurements, emphasizes the occurrence of a percolatingbehaviour characterized by percolation threshold at zero. Due to fast proton conduction acrossthe interconnected network formed by the polar groups, some samples showed very high room-temperatureconductivity up to 10 3 S cm 1.