The present study aims to investigate utilizing field-effect for inducing heterogeneous surface charge and consequently changing the fluid flow in a solid-state nanochannel with converging-diverging periodicity. It is shown that the combination of geometry and applied gate voltage (V_{ G}) would generate heterogeneous surface charge at the channel walls which can be modulated by V_{ G}, i.e. a moderate V_{ G} (0.7-0.9 V) causes charge inversion in diverging sections of the channel while V_{ G} > 0.9 enables charge inversion in the entire channel but it is still non-uniform in each section. The results show that zeta ({ \zeta}) potential is a function of V_{ G} which shows a linear to non-linear transition due to dilution of electrolyte in agreement with density functional theory and Monte Carlo simulations. In contrast, electrolyte symmetry has a minor effect on the variation of { \zeta} potential. It is also shown that the difference in { \zeta} potential across the channel ({ \Delta}{ \zeta}) increases by dilution of electrolyte and utilizing a more symmetric electrolyte with lower valances. For the first time, it is shown that { \Delta}{ \zeta} presents a maximum with the V_{ G}. The V_{ G} corresponding to the maximum { \Delta}{ \zeta} decreases with both dilution of electrolyte and higher anion valance. This is of practical importance to overcome leakage current problem of field-effect fluidic devices. It is also shown that the velocity field can be altered by changing both electrolyte concentration and symmetry. However, applying VG was found to be a more efficient way than electrolyte modifications. This includes generating circulation inside the channel which is of prime importance for applications such as mixing or separation/trapping.
Categories: physics.app-ph physics.comp-ph physics.flu-dyn