Mismatches in electrokinetic properties between micro- and nanochannels give rise to superposition of electroosmotic and pressure-driven flows in the microchannels. Parabolic or similar flow profiles are known to cause the so-called hydrodynamic dispersion, which under certain conditions can be formally assimilated to an increase in the solute diffusivity (Taylor-Aris model). It is demonstrated theoretically that taking into account these phenomena modifies considerably the pattern of current-induced concentration polarization of micro/nanointerfaces as compared to the classical model of unstirred boundary layer. In particular, the hydrodynamic dispersion leads to disappearance of limiting current. At essentially "over-limiting" current densities, the time-dependent profiles of salt concentration in microchannels behave like sharp concentration "fronts" moving away from the interface until they reach the reservoir end of the microchannel. Under galvanostatic conditions postulated in this study, these "fronts" move with practically constant speed directly proportional to the current density. The sharp transition from a low-concentration to a high-concentration zone can be useful for the analyte preconcentration via stacking. The pattern of moving sharp concentration "fronts" has been predicted for the first time for relatively broad microchannels with negligible surface conductance. The Taylor-Aris approach to the description of hydrodynamic dispersion is quantitatively applicable only to the analysis of sufficiently "slow" processes (as compared to the characteristic time of diffusion relaxation in the transversal direction). A posteriori estimates reveal that the condition of "slow" processes is typically not satisfied close to current-polarized micro/nanointerfaces. Accordingly, to make the description quantitative, one needs to go beyond the Taylor-Aris approximation, which will be attempted in future studies. It is argued that doing so would make even stronger the dampening impact of hydrodynamic dispersion on the current-induced concentration polarization of micro/nanointerfaces.

The mechanism of the meniscus oscillations and the stripes formation within the deposited fatty acid monolayer is theoretically analyzed on the basis of a supposition of concentration polarization within the solution during the deposition process. The concentration polarization can lead to decrease of adhesion work, dynamic contact angle, and maximum deposition speed under dynamic conditions resulting in meniscus instability. The adhesion work is evaluated from the disjoining pressure isotherm at a given subphase composition taking into account the charge regulation for a fatty acid monolayer. The relation of the proposed mechanism to the known experimental facts and observations is discussed.

A mathematical model describing the concentration polarization in the three-phase contact region during the Langmuir-Blodgett deposition process is developed. It is shown that the stationary deposition is only possible when, in additional to convective fluxes, electrodiffusion ionic fluxes and corresponding concentration gradients are developed in the system. At a sufficiently low withdrawal speed, the occurring diffusion and migration ionic fluxes restore the steady-state ionic balance. As well, electric charge is accumulated in close vicinity to the three-phase contact line to produce a stationary electric field. The concentration polarization affects the parameters of the deposition process (dynamic contact angle, work of adhesion, maximum deposition rate) as well as morphology, composition, and structure of the deposited monolayer. When the withdrawal speed exceeds a critical value, the transport of counterions becomes insufficient to compensate interfacial charge in close vicinity to the three-phase contact line. Consequently, the electrostatic repulsion between the monolayers becomes sufficiently strong to disrupt the deposition process. The latter can result in meniscus instability. The proposed mechanism correlates with some experimental observations.

A mathematical problem is formulated and numerically solved for addressing the electric field and ionic concentration distributions developing around the three-phase contact line during the Langmuir-Blodgett deposition of charged monolayers. Compared to a previous paper dealing with the same effect (J. Phys. Chem. B 2004, 108, 13449), the present analysis is not restricted to the case of low deposition rates and small concentration changes. The obtained results show that, for sufficiently high deposition rates, the subphase composition substantially changes in the immediate vicinity of the three-phase contact line. It is shown that the predicted changes in the subphase composition can drastically affect the adhesion work and the dynamic contact angle. On this basis, the influence of the concentration polarization effect on meniscus behavior is discussed.

The influence of electrical interactions on the composition of Langmuir films is theoretically studied. The overlapping electric double layers in the region close to the three-phase contact line are described on the basis of the Poisson−Boltzmann equation, taking into account the dissociation of fatty acids and the counterion binding to the surface film. It is concluded that the composition of the monolayer changes insignificantly during the deposition at the considered equilibrium constants and ionic concentrations in the solution. The results of the theory are used to discuss instability mechanisms during the Langmuir wetting process.