Distributions of Ionic Concentrations and Electric Field around the Three-Phase Contact at High Rates of Langmuir−Blodgett Deposition

Abstract

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.

Ions Redistribution and Meniscus Relaxation during Langmuir Wetting Process

“…As shown in previous studies, − the deposition of charged Langmuir monolayers is strongly dependent on ion redistribution kinetics within the thee-phase contact zone. The ion redistribution is the most important relaxation process for charged monolayers as the electrostatic interaction between the monolayer and the substrate surface is strongly affected by the ionic distributions within the solution in close vicinity to the thee-phase contact line.…”

“…The ion redistribution is the most important relaxation process for charged monolayers as the electrostatic interaction between the monolayer and the substrate surface is strongly affected by the ionic distributions within the solution in close vicinity to the thee-phase contact line. The ion redistribution during the LB deposition process is a consequence of the initial misbalance of convective ion fluxes within the solution. − This effect is very similar to the concentration polarization effect well-known in electrochemistry, membrane science and electrokinetics of disperse systems. Under the conditions of the steady-state deposition, stationary ion concentration and electric potential profiles are formed within the three-phase contact zone.…”

“…The counterions and co-ions distributed within the diffuse parts of the electrical double layers (DL) at both charged interfaces become involved in convective motion. However the convective ions transfer itself is not sufficient to support steady-state balances of the partial ions fluxes within the three-phase contact zone. − As a result, due to initial misbalance of the ion fluxes, the ion concentration and electric potential profiles form within the solution. These profiles produce electro-diffusion ion fluxes acting additionally to the convective ion fluxes.…”

“…The well-known example of striped structures formed by a receding meniscus is the self-organized patterns produced during the Langmuir−Blodgett (LB) transfer of phospholipid (DPPC) monolayers. ,, The stripes within the LB films of DPPC are formed when the surface pressure is kept close to the phase transition from the liquid-expanded to liquid-condensed phase. Other insoluble monolayers as well as their mixtures can also be used for LB-patterning on the substrate surfaces of a different kind. ,,,, A particularly interesting example is the formation of striped patterns by charged fatty acid monolayers. , In the case of charged monolayers, the film transfer process and the deposited film properties can be controlled by regulating the amounts of different counterions and co-ions within the subphase because of their effect on monolayer composition, surface charge, surface potential, and electrical double layer thickness. , As well, due to the ion-exchange mechanisms, different metal ions (or other counterions) with specific properties (electronic, magnetic, etc.) can be incorporated into the patterned films in controlled amounts, which can be important for many applications.…”

Nanoaggregate shapes at the air/water interface

“…A mathematical model allows the quantitative description of the concentration polarization around the three-phase contact zone and provides information for the optimization of essential process parameters, such as the dynamic contact angle, the adhesion work and the maximum transfer rate, and how the surface patterning can be controlled. [137][138][139][140][141][142][143][144][145] The second strategy for large-area patterning with mesostructured features uses the LB transfer process to induce phase transitions (i.e., substrate-mediated condensation) for creating patterns near the three-phase contact line from a homogeneous DPPC Langmuir monolayer at the LE phase. 127,146 As seen by AFM, the resulting mesostructured DPPC pattern consists of alternating stripes with widths of about 800 nm separated by channels of about 200 nm in width (Fig.…”