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).