Nonlinear Electro-Osmosis

Yamamoto and Yamamoto (1981) studied human skin tissue and found the limit current of linearity to be about 10 pA/cm at a frequency of 10 Hz. Grimnes (1983b) studied electro-osmosis in human skin in vivo and found a strong polarity-dependent nonlinearity. The effect was stronger the lower the frequency, Figure 10.17 shows the dramatic effect with 20 V and 0.2 Hz, soon leading to skin breakdown. Nonlinearity of cardiac pacemaker CC electrodes made of noble metals and intended for use with pulses has been extensively studied (Jaron et al. 1969). 

Figure 8.40 Voltage—current curves showing electro-osmosis and strong nonlinearity in human skin in vivo. From Grimnes (1983b) by permission.

AC electro-osmosis (ACEO) is a nonlinear electrokinetic phenomenon of induced-charge electro-osmotic flow around electrodes applying an alternating voltage. 

Induced-charge electro-osmosis refers to nonlinear electro-osmotic flow of a liquid electrolyte, when an electric held acts on its own induced diffuse charge near a polarizable surface. 

AC electro-osmosis (ACEO) Nonlinear electrophoretic mobility... 

The possibility of nonlinear electro-osmotic flow, varying as tt a E, seems to have been first described by Murtsovkin [1, 16], who showed that an alternating electric field can drive steady quadrupolar flow around a polarizable particle (Fig. la). This effect has recently been unified with other nonlinear electrokinetic phenomena in microfluidics [2], such as AC electro-osmotic flow (ACEO) at microelectrodes [4, 11,12] (Fig. lb), DC electrokinetic jets at dielectric comers [5] (Fig. Ic), and nonlinear flows around metal posts [3] (Fig. Id-e). These are all cases of induced-charge electro-osmosis (ICEO) -the nonlinear electro-osmotic flow resulting from the action of an electric field on its own induced diffuse charge near a polarizable surface. 

Nonlinear Electrokinetic Phencmena, Figure 2 Physical mechanism for induced-charge electro-osmosis around an ideally polarizable metal cylinder... 

The possibility of nonlinear electro-osmotic flow driven by non-equilibrium space charge at large currents was predicted by S.S. Dukhin in the 1980s [6, 13]. He coined the term electroosmosis of the second kind, to distinguish it fi om electrokinetic phenomena of the first kind (whether linear or nonlinear), which involve quasi-equiUbrium double layers and non-zero bulk concentrations. In spite of appealing to very different physical mechanisms, the maximum velocity of second-kind electro-osmosis is argued to be the same as that described above for ICEO flow (Eq. (4)) ... 

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