A COMPARATIVE THEORETICAL STUDY OF POTENTIAL DISTRIBUTION AND CONDUCTIVITY IN CATION- AND ANION-EXCHANGE NANOPOROUS MEMBRANES FILLED WITH TERNARY ELECTROLYTES

Determination of Critical Dimensions of Microchannels to Ensure the Electrokinetic Biomolecule Preconcentration: Analytical and Numerical Studies

Preconcentration of biomolecules based on ion concentration polarization (ICP) has been splendidly applied to various biomedical and chemical processes. However, in many circumstances, biomolecule preconcentration could not occur due to the lack of full studies on the preconcentration mechanism, especially on the effect of microchannel dimensions. In this work, we provide analytical studies on the critical dimensions (minimum and maximum) of microchannels for the preconcentration of biomolecules. These formulas are verified with the numerical results by fully solving the coupled governing equations: Poisson-Nernst-Planck and Navier-Stokes experiments with appropriate boundary conditions and assumptions. In addition, we examine the impact of operational parameters, such as electric potentials and critical external pressures, on the formation of the preconcentration. Moreover, two important results are provided for the first time, including the position of the preconcentrated biomolecule region and the concentration enhancement factor of the biomolecules. These analytical and numerical results are consistent with experimental observations and, therefore, could provide sharp insight into the mechanism of biomolecule preconcentration and give useful guidelines to better design and optimize ICP-based microfluidic preconcentration devices.

Ion current rectification properties of non-Newtonian fluids in conical nanochannels

Ionic current rectification generated by the geometric asymmetry of conical nanochannels has gradually attracted attention, but most studies have been limited to Newtonian fluids. In this study, the ionic current rectification characteristics in conical nanochannels filled with non-Newtonian fluids are investigated by numerical simulations. Electroosmotic flow and ion transport in Sisko fluids are solved using the Poisson-Nernst-Planck equations and the Navier-Stokes equations. The effects of the Debye parameter, power-law indexes and applied voltage on the ionic current, axial potential, ion concentration, radial velocity and rectification ratio in the nanopores are investigated. When κRt = 1, the current rectification ratio increases with the increase of the power-law index. However, when κRt = 6, the current rectification ratio first increases and then decreases with the increase of the power law index, reaching the maximum value at n = 1.0. These findings have positive implications for the construction of some nanodevices such as nanofluidic diodes.

Ion and Water Transport in Ion-Exchange Membranes for Power Generation Systems: Guidelines for Modeling

Artificial ion-exchange and other charged membranes, such as biomembranes, are self-organizing nanomaterials built from macromolecules. The interactions of fragments of macromolecules results in phase separation and the formation of ion-conducting channels. The properties conditioned by the structure of charged membranes determine their application in separation processes (water treatment, electrolyte concentration, food industry and others), energy (reverse electrodialysis, fuel cells and others), and chlore-alkali production and others. The purpose of this review is to provide guidelines for modeling the transport of ions and water in charged membranes, as well as to describe the latest advances in this field with a focus on power generation systems. We briefly describe the main structural elements of charged membranes which determine their ion and water transport characteristics. The main governing equations and the most commonly used theories and assumptions are presented and analyzed. The known models are classified and then described based on the information about the equations and the assumptions they are based on. Most attention is paid to the models which have the greatest impact and are most frequently used in the literature. Among them, we focus on recent models developed for proton-exchange membranes used in fuel cells and for membranes applied in reverse electrodialysis.

Modelling of Ion Transport in Electromembrane Systems: Impacts of Membrane Bulk and Surface Heterogeneity

Artificial charged membranes, similar to the biological membranes, are self-assembled nanostructured materials constructed from macromolecules. The mutual interactions of parts of macromolecules leads to phase separation and appearance of microheterogeneities within the membrane bulk. On the other hand, these interactions also cause spontaneous microheterogeneity on the membrane surface, to which macroheterogeneous structures can be added at the stage of membrane fabrication. Membrane bulk and surface heterogeneity affect essentially the properties and membrane performance in the applications in the field of separation (water desalination, salt concentration, food processing and other), energy production (fuel cells, reverse electrodialysis), chlorine-alkaline electrolysis, medicine and other. We review the models describing ion transport in ion-exchange membranes and electromembrane systems with an emphasis on the role of micro- and macroheterogeneities in and on the membranes. Irreversible thermodynamics approach, “solution-diffusion” and “pore-flow” models, the multiphase models built within the effective-medium approach are examined as the tools for describing ion transport in the membranes. 2D and 3D models involving or not convective transport in electrodialysis cells are presented and analysed. Some examples are given when specially designed surface heterogeneity on the membrane surface results in enhancement of ion transport in intensive current electrodialysis.