2. Theory of ICEK within microfluidics
In classic electrokinetics, the interaction between the applied electric field and the non-conducting microchannel walls results in a linear relationship between the induced zeta potential and the applied electric field (Z. Wu & Li, 2008a). However, in non-linear ICEK, such correlation behaves differently. Theoretically, upon applying an electric field (E ) around a polarizable object immersed in an electrolyte, the field lines intersect with the conducting surfaces (Todd M Squires & Bazant, 2004). Due to the electrolyte’s conductivity (σ), a current of J = σE is induced in the solution which therefore drives positive ions toward one side of the object and negative ions into the other side (Fig. 1A, i ). The ions movement continues until the field lines are expelled by the screening charge cloud around the object and the steady state condtion is achieved (Fig. 1A, ii ).
The changes in surface charge density (q ) over time for an ideal polarizable object with no electrochemical reactions at the solid/liquid interface is obtained from equation (1) (Todd M Squires & Bazant, 2004).