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Geometry effect on electrokinetic flow and ionic conductance in pH-regulated nanochannels

Sadeghi, M ; Sharif University of Technology

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  1. Type of Document: Article
  2. DOI: 10.1063/1.5003694
  3. Abstract:
  4. Semi-analytical solutions are obtained for the electrical potential, electroosmotic velocity, ionic conductance, and surface physicochemical properties associated with long pH-regulated nanochannels of arbitrary but constant cross-sectional area. The effects of electric double layer overlap, multiple ionic species, and surface association/dissociation reactions are all taken into account, assuming low surface potentials. The method of analysis includes series solutions which the pertinent coefficients are obtained by applying the wall boundary conditions using either of the least-squares or point matching techniques. Although the procedure is general enough to be applied to almost any arbitrary cross section, nine nanogeometries including polygonal, trapezoidal, double-trapezoidal, rectangular, elliptical, semi-elliptical, isosceles triangular, rhombic, and isotropically etched profiles are selected for presentation. For the special case of an elliptic cross section, full analytical solutions are also obtained utilizing the Mathieu functions. We show that the geometrical configuration plays a key role in determination of the ionic conductance, surface charge density, electrical potential and velocity fields, and proton enhancement. In this respect, the net electric charge and convective ionic conductance are higher for channels of larger perimeter to area ratio, whereas the opposite is true for the average surface charge density and mean velocity; the geometry impact on the two latest ones, however, vanishes if the background salt concentration is high enough. Moreover, we demonstrate that considering a constant surface potential equal to the average charge-regulated potential provides sufficiently accurate results for smooth geometries such as an ellipse at medium-high aspect ratios but leads to significant errors for geometries having narrow corners such as a triangle. © 2017 Author(s)
  5. Keywords:
  6. Aspect ratio ; Association reactions ; Electroosmosis ; Least squares approximations ; Surface charge ; Surface potential ; Surface reactions ; Velocity ; Electric double-layer overlap ; Electroosmotic velocity ; Elliptic cross-sections ; Geometrical configurations ; Physicochemical property ; Point matching tech-nique ; Semi-analytical solution ; Wall boundary condition ; Geometry
  7. Source: Physics of Fluids ; Volume 29, Issue 12 , 2017 ; 10706631 (ISSN)
  8. URL: https://aip.scitation.org/doi/abs/10.1063/1.5003694