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The scheme of DLVO theory and the concept of fractal structure of flocs applied to the suspension of montmorillonite have revealed out the unique nature of this clay dispersion. In this context, two major regimes are recognized. The first is the electrostatically dispersed regime. And the second is the coagulated regime. In the former, the formation of a diffusive electric double layer (EDL) characterized by reciprocal Debye length measured from the surface of the particle is distinctively important. Intrinsic viscosity with electroviscous effects and yield stress are interpreted by the steric presence of EDL. In the latter, the unit of transportation is a coagulated floc with finite cohesive strength. Sedimentation process reflecting these factors is carefully observed to recognize the turbulence generation by the formation of large flocs at the moment of gel collapse. Waiting time prior to gel collapse was found to be determined reflecting the pH-dependent charging behavior. By taking into account the effect pH-dependent charge, the DLVO based two regimes are further categorized into five. The developed tools can be extensively used for the system involved with different ionic species, pH, volume fraction and organic substances.

Investigation of electroviscous effects is of interest to technologies that exploit transport of ions through ion exchange membranes, charged capillaries, and porous media. When ions move through such media due to a hydrostatic pressure difference, they interact with the fixed charges, leading to an increased hydraulic resistance. Experimentally this is observed as an apparent increase in the viscosity of the solution. Electroviscous effects are present in all electrochemical membrane-based processes ranging from nanofiltration to fuel-cells and redox flow batteries. Direct measurements of electroviscous effects varying the applied ionic current through Nafion membranes have, to the best of the authors&rsquo, knowledge, not yet been reported in literature. In the current study, electroviscous phenomena in different Nafion ion exchange membranes are measured directly with a method where the volume permeation is measured under constant trans-membrane pressure difference while varying the ion current density in the membrane. The direct measurement of the electroviscous effect is compared to the one calculated from the phenomenological transport equations and measured transport coefficients. Within the experimental uncertainty, there is a good agreement between the two values for all membranes tested. We report here an electroviscous effect for all Nafion membranes tested to be &kappa, H?&kappa, H&minus, 1=1.15&minus, 0.052+0.035.

The electroviscous effect has been widely studied to investigate the effect of surface charge-induced electric double layers (EDL) on the pressure-driven flow in a micro/nano channel. EDL has been reported to reduce the velocity of fluid flow and increase the fluid drag. Nevertheless, the study on the combined effect of EDL with large zeta potential up to several hundred millivolts and surface charge depenedent-slip on the micro/nano flow is still needed. In this paper, the nonlinear Poisson–Boltzmann equation for electrical potential and ion distribution in non-overlapping EDL is first analytically solved. Then, the modified Navier–Stokes equation for the flow considering the effect of surface charge on the electrical conductivity of the electrolyte and slip length is analytically solved. This analysis is used to study the effect of non-overlapping EDL with large zeta potential on the pressure-driven flow in a microchannel with no-slip and charge-dependent slip conditions. The results show that the EDL leads to an increase in the fluid drag, but that slip can reduce the fluid drag. When the zeta potential is large enough, the electroviscous effect disappears for flow in the microchannel under a no-slip condition. However, the retardation of EDL on the flow and the enhancement of slip on the flow counteract each other under a slip condition. The underlying mechanisms of the effect of EDL with large zeta potential on fluid drag are the high net ionic concentration near the channel wall and the fast decay of electrical potential in the EDL when the zeta potential is large enough.

Graphical abstract, Subcutaneous delivery of highly concentrated protein formulations is paramount for reducing healthcare cost and improving patient compliance, where reducing the solution viscosity of formulations is critical for drug delivery. The objective of this paper is to provide some mechanistic understanding about the contribution of electrostatic repulsion to the viscosity of protein solutions at high concentrations, along with the effect of excipients such as salts on relative viscosity. Proteins are treated as charged colloids in this paper. At high concentrations, the electrical double layer starts to overlap, and secondary electroviscous effect becomes significant in addition to primary electroviscous effect. In other words, the hydrodynamic volume of proteins plays a great role in influencing their solution viscosity because of the excluded volume effect. Currently, it is hypothesized that the high viscosity of concentrated protein solutions is attributed to formation of clusters due to either electrostatic attraction or hydrophobic interactions, especially for monoclonal antibodies, in which anybody molecules in high concentration formulations may form networks. Consequently, viscosity reduction in the presence of inorganic or organic salts in these formulations is due to breaking up of these networks. In this review, authors hope to provide another point of view based on the effect of the electrostatic repulsion on the excluded volume-hydrodynamic volume. Finally, authors hope the proposed theoretical framework can be used to guide excipient selection in the product development of highly concentrated proteins.

The water and ion transport through a mesoporous γ-alumina membrane and a microporous organosilica membrane was simulated using the extended Nernst Planck equation combined with models for Donnan, steric and dielectric interfacial exclusion mechanisms. Due to the surface charge within the pore, the electroviscous effect was introduced in the model. The modified model fits well the rejection and permeability data for both membranes. The organosilica membrane shows a higher selectivity compared to the γ-alumina membrane, but the permeate flux is lower. At low ionic strength the electroviscous effect lowers the water flux through the γ-alumina membrane. The electroviscous effect is negligible for the organosilica membrane because its absolute surface potential ( 20 mV) is low compared to the γ-alumina membrane ( 60 mV). The simulation shows that the electroviscous effect should be included for the membranes with high surface potential (420 mV) and a pore size below 2–5 times of the electroviscous double layer thickness.