Order Parameter Description of Electrochemical-Hydrodynamic Interactions in Nanochannels

A novel phase-field model is developed for the quantitative modeling of the complex electrochemical-hydrodynamic interactions in narrow fluidic confinements. Through an order parameter variation, this model captures the underlying excluded volume effects, solvation interactions, and preferential polarizabilities in a self-consistent fashion, without resorting to computationally prohibitive molecular dynamics simulations. Agreement with molecular dynamics predictions is found to be quantitative.

Figure 1

(Left) Comparisons with results of Qiao and Aluru [3]: (a) anion and water concentrations (continuous lines represent MD predictions [3], whereas markers show present simulation predictions), (b) velocity profiles across the channel; for channel $\mathrm{\text{width}}=3.49\mathrm{nm}$, ${\sigma }_{\mathrm{surf}}=0.12\mathrm{C}/{\mathrm{m}}^2$, $E=-0.55\mathrm{V}/\mathrm{nm}$, $T=300\mathrm{K}$. (Right) Comparisons with results of Huang et al. [2]: (c) normalized charge density profiles for anions (−), cations (+), and solvent (water) for NaI and NaCl solutions, (d) velocity profiles expressed in terms of equivalent zeta potentials, for the above solutions and different ${\sigma }_{\mathrm{surf}}$ values, with the ranges of $E$ taken between 0.05 and $0.4\mathrm{V}/\mathrm{nm}$. For other simulation data, see Huang et al. [2]. Mesoscopic description of near-wall hydrophobic interactions is implemented following the earlier studies of Chakraborty [14]. Continuous lines represent MD predictions [2], whereas markers show present simulation predictions.