2013/03/21 by Mathias Dietzel, Dietzel, Mathias, Steffen Hardt +1 · 1 citation
Chemistry · Engineering · #Electrostatics and Colloid Interactions #FOS: Physical sciences #Fluid Dynamics (physics.flu-dyn) #Membrane-based Ion Separation Techniques #Nanopore and Nanochannel Transport Studies
paper · pdf · doi:10.48550/arxiv.1303.5455
openalex publication_date 2013/03/21 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
The effect of an axial temperature gradient on the flow profile and the\ninduced streaming potential of a pressure-driven symmetric electrolyte in a\nslit channel is investigated. Based on the non-isothermal Nernst-Planck\nequations as well as the Poisson equation in the lubrication approximation,\nexpressions for the ion distribution in the electric double layer (EDL) are\nderived. It is found that thermophoretic ion motion and a temperature-dependent\nelectrophoretic ion mobility increase the local EDL thickness with temperature,\nwhereas a temperature-dependent permittivity shrinks the EDL. Within the\nDebye-H "uckel approximation, the Navier-Stokes equation with the corresponding\nelectric body force terms is solved. Analytical expressions for the flow\nprofile and the induced (streaming) field under non-isothermal conditions are\nderived. It is shown that for such a situation the induced electric field is\nthe linear superposition of at least seven individual contributions. For very\nwide channels, only the thermoelectric field typically present in bulk\nelectrolytes when subjected to a temperature gradient (Soret equilibrium) as\nwell as the conventional pressure-induced streaming field are of importance.\nUnder extreme confinement, selective thermo-electro-migration driven by the\ninterplay between the temperature-dependent electrophoretic ion mobility and\nthe interaction of the ions with the surface wall charge causes a\nthermoelectric field of non-advective origin. For wider channels and besides\nthe well-known thermoosmosis due to the temperature dependence of the\ndielectric permittivity, it is demonstrated that a temperature gradient renders\nthe ion cloud in the EDL out of mechanical equilibrium. This leads to a\nthermoosmotic flow, and the ion advection affiliated with it may induce a\nthermoelectric field of similar order of magnitude as the one caused by more\nconventional thermal effects.\n