Session: 14-10-02: Micro/Nanofluidics 2025 II

Paper Number: 166638

Voltage Independent Diffusion Coefficients of Ions in Polymer Nanochannels by Transient Current Measurement 

The ion diffusion coefficient in a nanochannel represents the rate at which ions migrate through a nanoscale channel from higher concentration to lower concentration regions. This parameter, indicative of ion mobility, is governed by factors such as the channel's dimensions, geometry, surface charge, and the ionic strength of the solution. Particularly in nanochannels, the surface charge properties of the channel walls play a critical role in ionic transport, especially under low salt concentrations where the electric double layer thickness becomes larger. The slow equilibration of surface charge can have a pronounced impact on ion diffusion behavior within these confined environments.

One method to estimate the diffusion coefficients of ions in nanochannels is to measure transient current (conductance) while the concentration of the connecting microchannels varies. However, a significant challenge in this measurement arises from the potential influence of the applied voltage on ion mobility. An external electric field can enhance ion movement, leading to a diffusion coefficient that reflects both natural diffusion and voltage-driven effects.

In this study, we aim to measure the effective diffusion coefficient of ions in a polymeric straight nanochannel by applying Fick's law. The experimental procedure begins by filling the nanochannel with a low-concentration ionic solution, followed by introducing a high-concentration solution at the ends of the channel. This concentration gradient initiates diffusion within the nanochannel. To capture the dynamics of this process, a brief voltage pulse is applied to induce ionic motion, and the ionic current is measured over time. The resulting current-time data is analyzed by fitting it to Fick’s law, enabling the calculation of the diffusion coefficient. To address the influence of the applied voltage, we conducted a series of experiments using different voltage levels, specifically 20 mV, 35 mV, 50 mV, and 100 mV. For each voltage condition, the diffusion coefficient was calculated and analyzed. By comparing these results, we were able to isolate the intrinsic diffusion coefficient, which is independent of any voltage-driven contributions. Then, we will have voltage-independent diffusion coefficients of Ions in polymer nanochannels by transient current measurement 

The findings of this study provide insights into the fundamental mechanisms governing ion transport in nanoscale polymeric channels. Our approach highlights the importance of carefully accounting for external driving forces when measuring diffusion coefficients in confined systems. Additionally, the methodology developed in this research offers a reliable framework for characterizing ionic diffusion in various nanochannel systems, paving the way for applications in fields such as biosensing, and nanofluidics.

Presenting Author: Hooman Abdolvand Luoisiana State University

Presenting Author Biography: I am a third-year Ph.D. student at Louisiana State University (LSU), specializing in biosensing of biomolecules using in-plane polymeric nanopores. My research focuses on the development and application of advanced nanopore technologies for precise molecular detection, with potential applications in medical diagnostics and biotechnology.

My work integrates nanotechnology, polymer science, and biosensing, aiming to enhance the sensitivity and efficiency of nanopore-based detection systems. My contributions to the field include experimental and theoretical advancements in nanopore design and characterization.

Authors:

Hooman Abdolvand Luoisiana State University
Halle Davis Louisiana state university
Ramin Riahipour Louisiana state university
Sunggook Park Louisiana state university