Modeling of electrokinetic transport in silica nanofluidic channels

Abstract

We present a theoretical and numerical modeling study of the multiphysicochemical process in electrokinetic transport in silica nanochannels. The electrochemical boundary condition is solved by considering both the chemical equilibrium on solid-liquid interfaces and the salt concentration enrichment caused by the double layer interaction. The transport behavior is modeled numerically by solving the governing equations using the lattice Poisson-Boltzmann method. The framework is validated by good agreements with the experimental data for all range of ionic concentrations. The modeling results suggest that when the double layers interact, the bulk salt concentration enrichment results in the saturation of conductances for low ionic concentrations. Both the streaming conductance and the electrical conductance are enhanced by the double layer interaction, and such enhancements diminish when the channel size is larger than 10 times of the Debye length. The streaming conductance increases with pH almost linearly when pH<8, while the electrical conductance increases with pH exponentially.

Hydronium-dominated ion transport in carbon-dioxide-saturated electrolytes at low salt concentrations in nanochannels

“…Of particular interest is the intricate interplay among surface chemistry, electrokinetics, and fluid dynamics spanning over molecular and continuum macroscopic length scales [4,5]. It has been demonstrated that the electrokinetic properties at this scale have enabled a range of innovations including those for chemical sensing and bioanalytics [6][7][8][9][10][11][12], energy harvesting systems, [13][14][15][16][17][18], and nanofluidic ion transport [19][20][21][22][23][24][25][26], including enrichment, depletion, and rectification effects [27][28][29][30][31][32].…”

Electroviscous effect on the streaming current in a pH-regulated nanochannel

“…In contrast to previous works focused mainly on full numerical simulations [5][6][7][11][12][13][14][16][17][18] or based on the Debye-Hückel approximation (low surface potential) [15], analytical expressions are derived for the first time to predict the streaming electric field (E str ), streaming current (I str ), and streaming conductance (S str ) taking into account the electroviscous and Stern layer effects, the presence of H + and OH − ions, and surface chemistry reactions on the dielectric nanochannel wall. The developed model is applicable to any level of the surface potential in the entire pH range in nanofluidic experiments.…”

“…2b). Such apparent reduction of S str implies that neglecting the electroviscous effect on the estimation of the streaming current in nanofluidics, usually assumed in the literatures [1,[8][9][10][11][12][13]18,19], is inappropriate and might result in an incorrect estimation for relevant ion transport phenomena. Fig.…”

“…This phenomenon is typically known as the electroviscous effect because the liquid appears to have a higher viscosity in the vicinity of the charged nanochannel [14][15][16][17], resulting in a reduction in the streaming current. However, this effect was often neglected in the previous theoretical analysis of the streaming current in the nanochannel [1,[8][9][10][11][12][13]18,19]. Although this assumption dramatically simplifies the mathematical analysis, results in these studies show that under certain conditions such neglect may yield an incorrect estimation in pressure-driven ion transport phenomena [1,2,20,21].…”

“…Many experimental and theoretical studies demonstrated that the streaming current can provide a simple and effective scenario for converting hydrostatic energy to electrical power [2][3][4][5][6][7][8][9][10][11][12][13][14]. This clean energy harvesting system might open a new avenue in the exploration of new sources for renewable energy [4].…”