arXiv subjects

Bowen Ai

Publications and source records attributed to Bowen Ai.

5 recordsLinked to original sources

arXiv2025

Characteristics of mono-, di-, and trivalent cations in electric double layers: a molecular dynamic investigation

Ionic behaviors, including ion distributions and hydration characteristics at solid-liquid interfaces, are important research interests in many important applications, such as electric double-layer capacitors and water lubrication. Here, we systematically investigated the concentration distributions, hydration numbers, and screening properties of Li+, Na+, K+, Ca2+, Mg2+, and La3+ ions inside electric double layers (EDLs) at various charge densities. For the surface charge density weaker than -0.16 C m-2, monovalent cations mainly accumulate in the outer Helmholtz plane (OHP). As the charge density magnitude increases, monovalent cations start to dehydrate and migrate to the inner Helmholtz plane (IHP), following the order of K+, Na+, and Li+. This size-dependent behavior arises from the lower hydration energy of larger ions. While for the di- and trivalent ions, no obvious IHP appears. Based on ion distributions, the screening effect of counterions on surface charges is evaluated by analyzing the net charge distributions. As the charge density changes from 0 to -0.32 C m-2, due to the stronger accumulation of cations in EDLs, the location of the neutral plane changes from ~1.2 to ~0.4 nm. When the charge density reaches a threshold, excessive accumulation of cations can induce charge inversion. The threshold value and the maximum reversed charge are found to correlate with the ion size, cation valence, and concentration.

physics.chem-ph↗

arXiv2025

Ion transport through differently charged nanoporous membranes: from a single nanopore to multi-nanopores

Nanoporous membranes, leveraging their high-throughput characteristics, have been widely applied in fields such as molecular separation and energy conversion. Due to interpore interactions, besides the applied voltage and solution environment, the ion transport properties in porous membranes are influenced by the pore number and spacing. Here, to understand and control the transport properties of nanopore arrays, we systematically investigate the ion transport characteristics through membranes with different charge properties, pore numbers, and interpore distances. Using numerical simulations, we analyzed local ionic concentrations and electric potential in nanopore arrays containing nanopores with uniformly charged walls as well as unipolar diodes i.e., pores containing a junction between a charged zone and a neutral zone, and showed significant ion concentration polarization (ICP) for all studied cases. As the number of pores increased and the interpore spacing decreased, the enhanced interpore interactions through ICP led to a greater deviation of the total ionic current from the linear superposition of single-pore currents. Conversely, in bipolar nanopores whose walls contain a junction between positively and negatively charged zones ICP becomes negligible, and interpore interactions are substantially reduced. Furthermore, for membranes with various charge properties, the total current through nanopore arrays presents different quantitative dependence on the pore number under varying pore spacings. Our findings clarify the mechanism of interpore interactions in modulating ion transport through porous membranes, providing critical insights for designing nanofluidic devices based on nanopore arrays, such as nanopore-array sensors.

cond-mat.soft↗

arXiv2025

Ionic current rectification under concentration gradients and its application in evaluating surface charge properties of micropores

Ionic current rectification (ICR) induced by electroosmotic flow (EOF) under concentration gradients can find many applications in micro/nanofluidic sensing and ionic circuits. Here, we focused on the cases with micropores of moderate length-diameter ratios, through experimental research and systematical simulations, the EOF-induced ICR was found to exhibit voltage-dependent ratios. In the considered cases with a weak EOF or strong ionic diffusion, a large deviation appears between the ion concentration inside the micropore and the bulk value, which fails the prediction by solution conductivity gradients. Based on our simulation results, effective equations were developed for the theoretical description of ion concentration distributions along the micropore axis under coupled concentration gradient and electric field. With the predicted ion distributions inside micropores, the ICR ratio can be conveniently calculated with the derived electrical resistance of the microfluidic system, which applies to micropores of 200 to 1000 nm in diameter. Because the surface charge density is the only unknown input parameter, our developed equations can be used to evaluate the surface charge density of micropores with the measured EOF-induced ICR ratio under concentration gradients.

physics.chem-ph↗

arXiv2024

Detection of Nanopores with the Scanning Ion Conductance Microscopy: A Simulation Study

During the dielectric breakdown process of thin solid-state nanopores, the application of high voltages may cause the formation of multi-nanopores on one chip, which number and sizes are important for their applications. Here, simulations were conducted to mimic the investigation of in situ nanopore detection with scanning ion conductance microscopy (SICM). Results show that SICM can provide accurate nanopore location and relative pore size. Detection resolution is influenced by the dimensions of the applied probe and separation between the probe and membranes, which can be enhanced under large voltages or a concentration gradient.

physics.chem-ph↗

arXiv2024

Ion Transport through Short Nanopores Modulated by Charged Exterior Surfaces

Short nanopores find extensive applications capitalizing on their high throughput and detection resolution. Ionic behaviors through long nanopores are mainly determined by charged inner-pore walls. When pore lengths decrease to sub-200 nm, charged exterior surfaces provide considerable modulation to ion current. We find that the charge status of inner-pore walls affects the modulation of ion current from charged exterior surfaces. For 50-nm-long nanopores with neutral inner-pore walls, charged exterior surfaces on the voltage (surfaceV) and ground (surfaceG) sides enhance and inhibit ion transport by forming ion enrichment and depletion zones inside nanopores, respectively. For nanopores with both charged inner-pore and exterior surfaces, continuous electric double layers enhance ion transport through nanopores significantly. The charged surfaceV results in higher ion current by simultaneously weakening ion depletion at pore entrances and enhancing the intra-pore ion enrichment. The charged surfaceG expedites the exit of ions from nanopores, resulting in a decrease in ion enrichment at pore exits. Through adjustment in the width of charged-ring regions near pore boundaries, the effective charged width of the charged exterior is explored at ~20nm. Our results may provide a theoretical guide for further optimizing the performance of nanopore-based applications, like seawater desalination, biosensing, and osmotic energy conversion.

physics.chem-ph↗