Critical Behavior of the Electrical Conductivity of Concentrated Electrolytes: Ethylammonium Nitrate in n-Octanol Binary Mixture

Abstract

The electrical conductivity κ of highly concentrated binary ionic mixtures of ethylammonium nitrate in n-octanol at a critical salt mole fraction x = 0.766 and at an off-critical one x = 0.908 was measured over an extended temperature range above the critical consolute point. Far from the critical temperature T _c, the conductivity is accurately described by the Vogel–Fulcher–Tammann (VFT) law. However, in a temperature range ΔT = (T − T _c) ≤ 3 K, the conductivity exhibits a monotonous deviation from the VFT behavior. This anomaly is finite at T _c and, for the critical mixture, its amplitude is ≅ 0.23% of κ (T _c). The asymptotic behavior of the conductivity anomaly is described by a power law τ^{(1 − α)}, with τ = (T − T _c)/T _c, the reduced temperature, and α, the critical exponent of the specific heat anomaly at constant pressure. This critical anomaly is similar to the one observed in other highly concentrated critical electrolytes. The degree of dissociation of the salt for the critical mixture, α_diss ≅ 0.78 ± 0.04, is estimated from the value of the Walden product computed at T _c, and accounts for the effective free ion concentration in the reduced critical coordinates of the system.