Dynamic aspects of electroosmotic flow in a cylindrical microcapillary Yuejun Kang, Chun Yang * , Xiaoyang Huang School of Mechanical and Production Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore Received 11 June 2002; accepted 7 August 2002 (Communicated by E.S. S ßUHUBI) Abstract Dynamic aspects of the electroosmotic flow (EOF) in a cylindrical capillary are analysed. An analytical solution for electrostatic potential of the double layer has been derived by solving the complete Poisson– Boltzmannequationforarbitraryzeta-potentialsunderananalyticalscheme.TransientEOFfieldinresponse to the application of time dependent electric field is obtained analytically by using GreenÕs function method. Specifically, sinusoidally alternating (AC) electric fields are used to study the effect of frequency-dependent oscillation on the EOF. Limiting cases of zero frequency and pulsed electric field are also discussed. Ó 2002 Published by Elsevier Science Ltd. Keywords: Dynamic electroosmotic flow; Oscillating microchannel flow; AC electric field; Boltzmann distribution; Cylindrical capillary 1. Introduction Electroosmosis refers to the relative motion of polar media adjacent to a charged solid surface under the application of a tangential electric field. Generally, most surfaces acquire a certain amount of electrostatic charges when they are brought into contact with a polar medium. Such surface charges, in turn, cause both counter-ions and co-ions in the liquid to be preferentially redistributed, leading to the formation of an electric double layer (EDL) [1]. Conceptually, the EDL can be divided into an inner compact layer and an outer diffuse layer. The inner layer, usually of several Angstroms, is immediately next to the charged surface and contains a layer of * Corresponding author. Tel.: +65-6790-4883; fax: +65-6791-1859. E-mail address: mcyang@ntu.edu.sg (C. Yang). 0020-7225/02/$ - see front matter Ó 2002 Published by Elsevier Science Ltd. PII:S0020-7225(02)00143-X International Journal of Engineering Science 40 (2002) 2203–2221 www.elsevier.com/locate/ijengsci