Thermal diffusion of ionic species in charged nanochannels

TL;DR

This study uses molecular dynamics to explore how nanoconfinement and surface charges influence thermal diffusion of ions in charged nanochannels, revealing structural factors that control the Soret coefficient and thermal diffusivity.

Contribution

It provides new insights into the effects of nanoconfinement and surface charges on ionic thermal diffusion, with a novel MD simulation approach for nanoscale heat and mass transfer.

Findings

Nanoconfinement and surface charges can make solutions more thermophilic.

The sign and magnitude of the Soret coefficient are controlled by interfacial structural modifications.

Thermal diffusion in boundary layers differs significantly from bulk solutions.

Abstract

Diffusion of ions due to temperature gradients (known as thermal diffusion) in charged nanochannels is of interest in several engineering fields, including energy recovery and environmental protection. This paper presents a fundamental investigation of the thermal diffusion of sodium chloride in charged silica nanochannels performed by molecular dynamics (MD). The results reveal the effects of nanoconfinement and surface charges on the sign and magnitude of the Soret coefficient. It is shown that the sign and magnitude of the Soret coefficient are controlled by the structural modifications of the interfacial solutions. These modifications include the ionic solvation and hydrogen bond structure induced by the nanoconfinement and surface charges. The results show that both nanoconfinement and surface charges can make the solutions more thermophilic. Furthermore, the thermal diffusion of solutions in boundary layers is significantly different from that of solutions in bulk fluid, contributing to the overall difference between the thermal diffusivity of pore fluid and that associated with bulk fluid. The findings provide further understanding of thermal diffusion in nano-porous systems. The proposed MD simulation methodology is applicable to a wider category of coupled heat and mass transfer problems in nanoscale spaces.