Thermodiffusion in the Critical Region

Abstract

Abstract. Long range fluctuations of the order parameter affect thermodynamic as well as transport properties in the critical region. The values of transport coefficients near a critical point are typically enhanced compared to the values in the classical region far away from a critical point. Asymptotically close to a critical point, the critical enhancements obey power laws with universal critical exponents. The asymptotic critical region is surrounded by a large crossover region, where the enhancements are no longer asymptotic but still significant compared to the background values. In binary mixtures, this is also the region where differences are observed in the critical behavior of transport coefficients near liquid-liquid (consolute) and liquid-vapor (plait) critical points. In this contribution, we review the critical dynamics of binary fluid mixtures with a focus on thermodiffusion.

The rich phase behavior of the thermopolarization of water: from a reversal in the polarization, to enhancement near criticality conditions

“…Our results distinctly show a strong enhancement in the thermal polarization as the critical point is approached. For the closest temperature to the critical point investigated here, the TP coefficient increases by two orders of magnitude as compared with the values obtained at T ∼ 300 K. It has been discussed before in the context of binary mixtures, that the Soret coefficient diverges at the critical point 23 . Experiments of anilinecyclohexane mixtures 44 agree with the predictions from theoretical arguments, and good agreement is obtained with the asymptotic power law and the corresponding exponent.…”

“…the Soret coefficient diverges as the critical point is approached. In general, transport coefficients behave anomalously in the critical region too 22,23 . Hence, we want to investigate whether a similar enhancement behavior can be observed in the TP effect.…”

Temperature Dependence of Soret Coefficient in Aqueous and Nonaqueous Solutions of Pullulan

“…Under poor solvent conditions close to a critical temperature the Soret coefficient diverges due to the critical slowing down, but D T remains constant. [40][41][42] For aqueous solutions of polymers the Soret coefficient shows often a complicated temperature and concentration dependence. The Soret coefficient S T of poly(ethylene oxide) [PEO] in the solvent mixture ethanol/water increases with temperature, whereas the slope is positive and decreases with increasing water content.…”

Piston effect induced by cross-boundary mass diffusion in a binary fluid mixture near its liquid-vapor critical point

“…Asymptotically close to the critical point, both D s and D b tend to zero due to the strong divergences of ξ and the concentration susceptibility, respectively. According to Luettmer-Strathamann [21], asymptotically close to the critical point, the following power laws hold:…”

“…The one-dimensional model is justified since gravity is ignored (no buoyant convection and density stratification). The fluid is initially motionless at the critical density ρ c and at thermodynamic equilibrium slightly larger than its critical temperature T c (subscript c denotes the critical value [21]. The energy flux q and mass flux i are thus expressed as [23] (along the x direction)…”