Non-equilibrium electric double layers in narrow channels

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Non-equilibrium effects in electric double layers (EDLs) inside narrow electrolyte-filled channels will be studied theoretically based on the combined Poisson, Nernst-Planck, heat transport and Stokes equations. Firstly, the effects of an axial temperature gradient on an electrolyte-filled slit-channel will be investigated. The flow field due to the thermally-induced force imbalance in the EDL will be computed based on asymptotic expansions of the underlying system of equations. The effect of a temperature dependent wall zeta potential will also be considered. Apart from the analytical treatment of the equations, numerical solutions will be employed to test the range of validity of the analytical model and to explore the parameter space beyond this regime. Secondly, the influence of chemical reactions at the channel walls on electroosmotic flow (EOF) will be explored. When fresh electrolyte is introduced into a channel via advection, the chemical equilibrium at the walls is disturbed, potentially resulting in dynamic changes of the zeta potential. This effect and its influence on EOF will be studied based on a reduced-order model obtained from averaging over the channel cross section. The description will incorporate a simple model for the wall reactions and area-averaged transport terms for the diffusion, advection and electromigration of ions. The parameter studies with this model will be accompanied by experiments in which the EOF velocity as a function of time is measured. First experiments conducted in the group of the applicant have already indicated that the wall zeta potential may be a dynamic quantity influenced by the EOF inside the channel.