Counter-electroosmosis

Figure 6. A schematic of the electroosmotic flow of the medium (e.g., an electrolyte) in a capillary caused by the flow of counter ions as a plug, under the influence of the applied electric field, E UL, is the convective liquid velocity from electroosmosis. Adapted from Everett.48...

Safe and effective delivery of peptides has also been successfully demonstrated in human studies using iontophoresis, a technique that uses mild electric current to facilitate transport of molecules across the skin. ° Iontophoresis works primarily by a combination of two forces, electro-repulsion of charged drug molecule away from the electrode and into the skin, and electroosmosis, a convective solvent flow in the direction of the counter-ion transport. In general, cationic proteins and peptides are delivered more efficiently than anionic molecules because electro-osmosis works in the same direction as electro-migration for cationic species. 

The ionic species j represents both the ions migrating into the receiver from the donor including ionic species i and the oppositely charged counter-ions migrating into the donor from the receiver. In dominant electrotransport (negligible passive diffusion contribution) and combining the electroosmosis and electrophoresis terms in Eq. (6), Eq. (9) is commonly seen in the iontophoresis literature ... 

Electroosmosis. Electroosmosis occurs in systems with applied potentials and results from preferential adsorption of charges at a fixed surface, such as a column wall. This ionic adsorption results in the build-up of a charged counter layer at the surface, which migrates electrophoretically. This flux along the wall induces a convective flux in the bulk due to viscous shear. If... 

The pores form a DC current path. The sum of their conductances is so large that the capacitive effect of the membrane as a dielectric is small at low frequencies. If there are not too many pores, most of the potential difference is over the membrane pores, and the E-field strength in the pores will be high. The counter-ions of the double layer on the pore walls will migrate synchronous with the E-field, and the solution inside the pore will be pumped back and forth by electroosmosis. At higher frequencies, the membrane susceptance will shunt the pores, and voltage across the pore will be reduced. Counterion relaxation will also occur, as shown in Figure 3.11. 

This suggests that the initial curvature is driven by the pressure gradient caused in the ion gel by the electroosmosis flow. Hence, the initial curvature is a function of the ionic charge, Q, and the water transference coefficient, Xla, which describes the number of water molecules transferred per counter cation transferred. The experimentally determined initial curvature of an IPMC actuator (Naflon 117/Au) having various ionic forms could be reproduced with fidelity using the theoretical curves described by Eqs. 17, 18, and 20 (Yamaue et al. 2005). 

Figure 7.1 Schematic representation of five electrokinetic phenomena A) electrophoresis, B) electroosmosis, C) electroosmotic counter-pressure, D) streaming potential, and E) migration potential for details see text. In a clockwise as well as counterclockwise direction each one of these five electrokinetic phenomena depicted above stands in a simple relationship to its closest neighbors and indicate the polarity of an applied electric field P ...

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