Electrokinetics of Diffuse Soft Interfaces. 2. Analysis Based on the Nonlinear Poisson−Boltzmann Equation

Abstract

In a previous study (Langmuir 2004, 20, 10324), the electrokinetic properties of diffuse soft layers were theoretically investigated within the framework of the Debye-Hückel approximation valid in the limit of sufficiently low values for the Donnan potential. In the current paper, the electrokinetics is tackled on the basis of the rigorous nonlinearized Poisson-Boltzmann equation, the numerical evaluation of the electroosmotic velocity profile, and the analytically derived hydrodynamic velocity profile. The results are illustrated and discussed for a diffuse soft interface characterized by a linear gradient for the friction coefficient and the density of hydrodynamically immobile ionogenic groups in the transition region separating the bulk soft layer and the bulk electrolyte solution. In particular, it is shown how the strong asymmetry for the potential distribution, as met for high values of the bulk fixed charge density and/or low electrolyte concentrations, is reflected in the electrokinetic features of the diffuse soft layer. The analysis clearly highlights the shortcomings of the discontinuous approximation by Ohshima and others for the modeling of the friction and electrostatic properties of soft layers exhibiting high Donnan potentials. This is in line with reported electrokinetic measurements of various soft particles and permeable gels at low electrolyte concentrations which fail to match predictions based on Ohshima's theory.

The EOF of polymer solutions

“…Many efforts have been made, however, to describe the surface potential after analytes adsorption from dilute solutions [28][29][30][31][32][33]. On the other hand, models addressed to describe electrokinetic phenomena in polymer-coated surfaces also involve simple electrolyte solutions [34][35][36]. Evidently, modelling the full problem demands additional investigation.…”

“…Robust and stable coatings are also achieved by using successive multiple ionic layers [37]. According to [34][35][36], the non-draining condition means a relatively large frictional factor for the solvent inside the polymer layer. According to [27], the solid-like condition means that the fluid viscosity in the adsorption layer is much higher than that of the central zone.…”

Electrohydrodynamic Properties of Succinoglycan as Probed by Fluorescence Correlation Spectroscopy, Potentiometric Titration and Capillary Electrophoresis

“…The inhomogeneous nature of the charged polymer segments is an important feature of this representation of the diffuse interface. [27][28] The volumic charge density, Γ°, is obtained by dividing Q o by the volume V. As such, Γ°may be viewed as an average space charge density per macromolecule. Since the electrokinetic behavior of soft particles depends on space charge densities and not on the total amount of charges carried by the particle, we choose to report in the following the quantity Γ°(or equivalently Γ°/F with F the Faraday's number) when comparing experimental and theoretical protolytic data.…”

Influence of Metallic Ions on the Aggregation of Soft Colloidal Polysaccharides

“…The metal to polymer concentration ratio corresponds to the situation in which the polymer concentration is fixed and variable amounts of metal concentration solution are added to polymer solution. In order to reduce the complexity of the problem as connected to swelling and segment distribution heterogeneity [46][47][48], the analyses are carried out for CMD suspensions in 100 mM NaNO 3 electrolyte solution. In the first step of our study, we analysed the turbidimetry of CMD macromolecules in presence of variable concentrations of divalent cations Ca 2+ and Cd 2+ .…”