Multiscale Computation of Fluid and Ion Transport in Nanochannels: The Effect of Partial Charges

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We demonstrate a hierarchical multiscale methodology to solve ion transport in nanoscale channels and show that the partial charges from quantum calculations significantly alter transport properties and I-V plots for electrolytes in confined geometries. Effects of nanoscale confinement on the transport properties of ions and water need to be resolved for the characterization and design of nanochannel based devices. Though atomic scale simulations can be used to explicitly treat the finite size of ions and water, it is possible that in nanoscale channels the contribution of the quantum effects on the electrostatic interactions of the wall, such as the bond polarization effects can influence fluid transport properties. We employed a hierarchical multiscale approach that takes into account the quantum effects, by first calculating the atomic partial charges using the DFT, and then using these as inputs for the MD simulations to calculate the diffusion coefficient and mobility, and finally using these values in the continuum Poisson-Nernst-Planck equations to calculate the current-voltage characteristics. Contributions of the wall–electrolyte interactions are substantial in channel widths of the order of 1-2 nm. Electroosmotic flow is observed in uncharged channels because of the oscillations in ion density, which creates a local net charge density.

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Journal: TechConnect Briefs
Volume: 1, Technical Proceedings of the 2005 NSTI Nanotechnology Conference and Trade Show, Volume 1
Published: May 8, 2005
Pages: 601 - 604
Industry sector: Sensors, MEMS, Electronics
Topic: Micro & Bio Fluidics, Lab-on-Chip
ISBN: 0-9767985-0-6