Analysis of electro-kinetic pumping efficiency through finite-length nano-scale surface-charged capillaries

• Published in: Journal of electroanalytical chemistry (Lausanne, Switzerland) Switzerland), 2009-05, Vol.630 (1), p.1-9
• Main Authors: Chein, Reiyu, Chen, Hongjie, Liao, Chencheng
• Format: Article
• Language: English
• Subjects: Chemistry; Dimensionless Debye length; Electric double layer; Electro-kinetic pumping; Electrochemistry; Exact sciences and technology; General and physical chemistry; Maximum pumping efficiency; Study of interfaces; Surface charge density; Transport phenomena
• ISSN: 1572-6657; 1873-2569
• DOI: 10.1016/j.jelechem.2009.01.025

Electro-kinetic pumping efficiency using a two-dimensional axisymmetrical model is numerically investigated. A finite-length nano-scale surface-charged cylindrical capillary with reservoirs connected at the capillary ends is considered as the physical domain. The Navier–Stokes, Laplace, Poisson and Nernst–Planck equations are solved simultaneously to obtain the fluid flow, electric potential distribution and ion concentration distribution in the physical domain. The pumping efficiency predicted using a one-dimensional model assuming an infinitely long channel, Boltzmann ion distribution and equal ionic electrical mobility is also carried out and compared with the two-dimensional result. It is found that the surface charge density and dimensionless Debye length ( κa) magnitudes are the two parameters that determine the electro-kinetic pumping efficiency. The pumping efficiency is found to increase with the increase in surface charge density for κa in the 0.03–30 range. For all surface charge densities studied, higher maximum pumping efficiency can be obtained when the dimensionless Debye length ( κa) is less than 2. That is, an electrical double layer (EDL) overlap effect enhances the pumping efficiency. In this κa range, the maximum pumping efficiency predicted by the two-dimensional model is higher than that predicted by the one-dimensional model. For κa greater than 2, the maximum pumping efficiency predicted from both the one and two-dimensional models agree well. This implies that the one-dimensional model is suitable only when the EDLs are not overlapped.