On the microscopic origin of Soret coefficient minima in liquid mixtures

Abstract

Temperature gradients induce mass separation in mixtures in a process called thermodiffusion and quantified by the Soret coefficient. The existence of minima in the Soret coefficient of aqueous solutions at...

Non-monotonic Soret coefficients of aqueous LiCl solutions with varying concentrations

“…In this subsection, we follow the analysis as given in a recent paper by Gittus and Bresme, 27 who conducted simulations to study the thermodiffusion of Lennard-Jones mixtures under specific parameter settings. The basis of the analysis is the well-known expression for the Soret coefficient from irreversible-thermodynamics, which, applied to the present case of LiCL solutions, reads…”

“…In order to transform the data into a form more accessible to fitting procedures, and to be able to investigate the origin of emerging minima, we have followed the work by Gittus and Bresme 27 and analyzed the Soret coefficients in terms of their two dominant factors, i.e. a thermodynamic factor and the heat of transfer, the latter being the ratio of two Onsager coefficients .…”

“…First, we test whether a recently presented approach to discuss the minimum in S T in the context of overlapping hydration shells can be applied 18 and use an empirical equation to describe the Soret coefficient as a function of temperature and concentration. As the hydration model imposes a minimum, we followed a recent approach by Gittus and Bresme, 27 who found a correlation between the minimum of the thermodynamic factor and the Soret coefficient. As the thermodynamic data of aqueous solutions of LiCl are well known, we were able to calculate the ratio of the Onsager coefficients, which a simple function can describe.…”

“…At higher concentrations, the approach eventually breaks down, which might be related to cluster formation, which is not considered in the model. Recently, Gittus and Bresme 27 performed a Lennard-Jones simulation on a particular set of parameters and found a correlation between the minimum of the thermodynamic factor Γ and the Soret coefficient S T .…”

On the validity of some equilibrium models for thermodiffusion

“…A vast body of experimental and computational work has attempted to go beyond this picture and characterise the molecular determinants of thermodiffusion (see, e.g., [2]). While being an "old" problem, this remains a partly open question and a timely topic, with very recent work testing phenomenological thermodynamic models using molecular dynamics simulations of Lennard-Jones particles [5][6][7].…”