Frequency Effects on Periodical Potential and Ion Concentration Oscillation in Microchannel with an AC Electric Field Perpendicular to Wall

Without any approximation, this paper presents a numerical analysis of full Poisson-Nernst-Planck equation to investigate periodical potential and ion transport in microchannel under an AC electric field perpendicular to a wall in broad frequency range. Numerical solutions indicate that behavior of periodical potential and ion concentration oscillation strongly depend on frequency. The study found the follows: (1) In low frequency regions, amplitude of potential and ion concentration oscillations retains constants that are independent of frequency. With respect to applied potential, phase angles are close to zero. Electrolyte solution is fully charged in the microchannel. (2) In moderate frequency regions, amplitude of potential increases, and the phase angle first increases and then decreases, with the frequency increase. The amplitude of ion concentration oscillation decreases, but phase angle increases, with the frequency increase. A maximum phase angle is found at a moderate frequency. Electrolyte solution in the microchannel is partially charged. (3) In high frequency regions, amplitude of potential approaches a steady maximum that is independent of frequency, phase angle of potential decreases to zero, amplitude of ion concentration oscillation approaches zero, and phase angle reaches a steady maximum. Ion concentration is almost uniform in the microchannel. Induced charge density vanishes, and potential distribution shows a linear profile in the microchannel. The electrolyte solution in the microchannel can not be charged. Moreover, a double-frequency Fourier component of ion concentration oscillation is found by spectral analysis. Supported by National Science Foundation of China, No. 10872076, No. 50805059 (1) Corresponding author : Jiankang Wu, Professor, email: [email protected] 1632 Yao Zhang, Jiankang Wu and Bo Chen