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 Transform Infrared spectroscopy (FT-IR), X-rays Diffraction (XRD), and AC complex impedance spectroscopy. Driven by hydrogen bond interactions among HDEHP PO(4)H group and NMF CO and NH groups, and also by steric effects among the HDEHP alkyl chains, the system microstructure is mainly characterized by the coexistence of spatially separated hydrophilic and hydrophobic nanodomains showing local organization and short-range order. The evolution of this structural feature with system composition has been highlighted by FT-IR and XRD. On the other hand, the thermally activated proton mobility within these hydrophilic domains, as pointed out by AC complex impedance measurements, emphasizes the occurrence of a percolating behaviour characterized by percolation threshold at zero. Due to fast proton conduction across the interconnected network formed by the polar groups, some samples showed very high room-temperature conductivity up to 10(-3) S cm(-1).
Calandra
Pietro
P
Istituto per i Processi Chimico-Fisici, Consiglio Nazionale delle Ricerche, Sez. di Messina Salita Sperone, C.da Papardo 98158 Faro Superiore (ME), Italy. calandra@me.cnr.it
Passarello
Marco
M
Ruggirello
Angela
A
Liveri
Vincenzo Turco
VT