Ion-specific anomalous electrokinetic effects in hydrophobic nanochannels

DM Huang and C Cottin-Bizonne and C Ybert and L Bocquet, PHYSICAL REVIEW LETTERS, 98, 177801 (2007).

DOI: 10.1103/PhysRevLett.98.177801

We show with computer simulations that anomalous electrokinetic effects, such as ion specificity and nonzero zeta potentials for uncharged surfaces, are generic features of electro-osmotic flow in hydrophobic channels. This behavior is due to the stronger attraction of larger ions to the "vapor-liquidlike" interface induced by a hydrophobic surface. We propose an analytical model involving a modified Poisson-Boltzmann description for the ion density distributions that quantitatively predicts the anomalous flow profiles. This description includes as a crucial component an ion-size-dependent hydrophobic solvation energy. These results provide an effective framework for predicting ion-specific effects, with potentially important implications for biological modeling.

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