Critical Viscosity and Ising‐to‐Mean‐Field Crossover Near the Upper Consolute Point of an Ionic Solution

Abstract

We report on shear viscosity data near the upper consolute point of the ionic system tetrabutylammonium picrate+ 1-tridecanol (T, = 341.845 K) which shows a large mean-field region in its static critical properties with crossover to Ising behavior close to the critical temperature. After suitable assessment of the non-singular background viscosity we establish that the asymptotic scaling law q 0: T -y applies in the region T < 5 x where T = (T-T,)/T, is the reduced temperature. The value of the exponent is determined to y = 0.0434+0.001 which is close to the current best value for the 3d-Ising model, y = 0.041. At higher reduced temperatures pronounced deviations from king criticality are observed. In agreement with the mean-field prediction y = 0, the critical contribution is vanishing. This crossover is discussed in the framework of current theory.= 0.051. Second-order corrections (0.018 e 2 ) also yield

A Short History of Phase Transitions in Ionic Fluids

“…The scenario of Ising behavior with deviations that indicate a crossover towards mean-field behavior was stated by measurements of the viscosity [77] and of the phase diagrams [78] on the solutions of N 4444 Pic in alcohols. An analysis of the experimental results of the various systems including the measurements on the mixtures of N 2226 B 2226 in diphenylether and N 5555 Br in water in terms of the crossover theory [56] led to a consistent description with the same crossover parameters for phase diagrams, scattering -and turbidity measurements and a continuous change of the crossover parameter with the dielectric permittivity.…”

Critical viscosity of the ionic mixture triethyl n-hexyl ammonium triethyl n-hexyl borate in diphenyl ether

“…Only two measurements of the viscosity near the critical point of a nonaqueous ionic mixture have been reported. For tetra-n-butylammonium picrate in tridecanol, Kleemeier et al 21 found a critical anomaly with the viscosity exponent yϭ0.043Ϯ0.001, where the uncertainty was due to the uncertainty in the measured value of T c . This result is consistent with the viscosity exponents found in nonionic Isingtype systems, 13,22 even though turbidity measurements 23 had found mean-field behavior in a limited range of temperature.…”

Critical viscosity near the liquid–liquid phase transition in the solution of the ionic liquid 1-methyl-3-hexylimidazolium tetrafluoroborate in 1-pentanol

“…Viscosity measurements have played a decisive role in the experiments concerning the criticality of ionic solutions regarded as Coulomb systems. [9][10][11] The observation of mean-field critical exponents by the investigation of a phase diagram 12 and of the turbidity 13 in the near-critical region of a Coulomb system suggested the possibility that in those systems the long-range Coulomb forces may generally lead to mean-field criticality. The finding of mean-field criticality in such systems was believed to be in accordance with theoretical reasoning suggesting mean-field criticality for Coulomb systems.…”

“…16 The first measurements establishing that Coulomb phase transitions belong to the Ising universality class were indeed viscosity measurements. [9][10][11] The reason for Ising criticality in the ionic fluids rests on the shielding due to charge ordering described already by the classical Debye-Hu ¨ckel theory. Therefore, long-range Coulomb interactions become effectively short-range.…”