skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Ionic current driven by a viscosity gradient
Gradients of voltage, pressure, temperature, and salinity can transport objects in micro- and nanofluidic systems by well-known mechanisms. This paper explores the dynamics of particles in a viscosity gradient with numerical simulations. The different stochastic rules used to integrate the random motion of Brownian particles affect the steady-state distribution of particles in a diffusivity gradient. Importantly, the simulations illuminate the important role that the boundary conditions play, disallowing a steady-state flux when the boundary conditions mimic those of a closed container, but allowing flux when they mimic electrodes. These results provide an interpretation for measurements of a steady ionic current flowing between electrodes separated by a nanofluidic channel with a liquid viscosity gradient.  more » « less
Award ID(s):
1904511
PAR ID:
10472688
Author(s) / Creator(s):
;
Publisher / Repository:
The Royal Society of Chemistry
Date Published:
Journal Name:
Faraday Discussions
Volume:
246
ISSN:
1359-6640
Page Range / eLocation ID:
47 to 59
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; (, arxiv_25_d)
    Many viscous liquids behave effectively as incompressible under high pressures but display a pronounced dependence of viscosity on pressure. The classical incompressible Navier-Stokes model cannot account for both features, and a simple pressure-dependent modification introduces questions about the well-posedness of the resulting equations. This paper presents the first study of a second-gradient extension of the incompressible Navier-Stokes model, recently introduced by the authors, which includes higher-order spatial derivatives, pressure-sensitive viscosities, and complementary boundary conditions. Focusing on steady flow down an inclined plane, we adopt Barus' exponential law and impose weak adherence at the lower boundary and a prescribed ambient pressure at the free surface. Through numerical simulations, we examine how the flow profile varies with the angle of inclination, ambient pressure, viscosity sensitivity to pressure, and internal length scale. 
    more » « less
  2. ; (, Journal of the Atmospheric Sciences)
    Abstract Recent studies have demonstrated the sensitivity of simulated tropical cyclone (TC) intensity to horizontal diffusion in numerical models. It is unclear whether such sensitivity comes from the horizontal diffusion in or above the boundary layer. To address this issue, both an Ooyama-type model and a full-physics model are used to conduct sensitivity experiments with reduced or enlarged horizontal mixing length (lh) in the boundary layer and/or in the free atmosphere. Results from both models show that enlarging (reducing)lhthroughout the model domain considerably reduces (increases) the TC intensification rate and quasi-steady intensity. A new finding is that changinglhabove the boundary layer imposes a much greater influence than that in the boundary layer. Largelhabove the boundary layer is found to effectively reduce the radial gradient of tangential wind inside the radius of maximum tangential wind and thus the inward flux of absolute vorticity, reducing the positive tangential wind tendency and the TC intensification rate and the steady-state intensity. In contrast, although largerlhin the boundary layer reduces the boundary layer tangential wind tendency, it also leads to the more inward-penetrated inflow and thus enhances the inward flux of absolute vorticity, which offsets part of the direct negative contribution by horizontal diffusion, making the net change in tangential wind tendency not obvious. Results from three-dimensional simulations also show that the resolved eddies contribute negatively to TC spinup whenlhis small, while its effect weakens whenlhis enhanced either in or above the boundary layer. 
    more » « less
  3. ; ; (, Dryad)
    This dataset stores the data of the article The effect of Pliocene regional climate changes on silicate weathering: a potential amplifier of Pliocene-Pleistocene cooling P. Maffre, J. Chiang & N. Swanson-Hysell, Climate of the Past). This study uses a climate model (GCM) to reproduce an estimate of Pliocene Sea Surface Temperature (SST). The main GCM outputs of this modeling (with a slab ocean model) are stored in "GCM_outputs_for_GEOCLIM/", as well as the climatologies from ERA5 reanalysis. The other GCM outputs that were used in intermediary steps (coupled ocean-atmosphere, and fixed SST simulations) are stored in "other_GCM_outputs/". The forcing files (Q-flux) and other boundary conditions to run the "main" GCM simulations can be found in "other_GCM_outputs/Q-flux_derivation/", as well as the scripts used to generate them. Secondly, the mentioned study uses the GCM outputs in "GCM_outputs_for_GEOCLIM/" as inputs for the silicate weathering model GEOCLIM-DynSoil-Steady-State (https://github.com/piermafrost/GEOCLIM-dynsoil-steady-state/tree/PEN), to investigate weathering and equilibrium CO2 changes due to Pliocene SST conditions. The results of these simulations are stored in "GEOCLIM-DynSoil-Steady-State_outputs/". The purpose of this dataset is to provide the raw outputs used to draw the conclusions of Maffre et al. (2023), and to allow the experiments to be reproduced, by providing the scripts to generate the boundary conditions. 
    more » « less
  4. ; ; (, arxiv_25_b)
    We introduce second-gradient models for incompressible viscous fluids, building on the framework introduced by Fried and Gurtin. We propose a new and simple constitutive relation for the hyperpressure to ensure that the models are both physically meaningful and mathematically well-posed. The framework is further extended to incorporate pressure-dependent viscosities. We show that for the pressure-dependent viscosity model, the inclusion of second-gradient effects guarantees the ellipticity of the governing pressure equation, in contrast to previous models rooted in classical continuum mechanics. The constant viscosity model is applied to steady cylindrical flows, where explicit solutions are derived under both strong and weak adherence boundary conditions. In each case, we establish convergence of the velocity profiles to the classical Navier-Stokes solutions as the model's characteristic length scales tend to zero. 
    more » « less
  5. ; ; (, Journal of Rheology)
    Discrete-particle simulations of bidisperse shear thickening suspensions are reported. The work considers two packing parameters, the large-to-small particle radius ratio ranging from [Formula: see text] (nearly monodisperse) to [Formula: see text], and the large particle fraction of the total solid loading with values [Formula: see text], 0.5, and 0.85. Particle-scale simulations are performed over a broad range of shear stresses using a simulation model for spherical particles accounting for short-range lubrication forces, frictional interaction, and repulsion between particles. The variation of rheological properties and the maximum packing fraction [Formula: see text] with shear stress [Formula: see text] are reported. At a fixed volume fraction [Formula: see text], bidispersity decreases the suspension relative viscosity [Formula: see text], where [Formula: see text] is the suspension viscosity and [Formula: see text] is the suspending fluid viscosity, over the entire range of shear stresses studied. However, under low shear stress conditions, the suspension exhibits an unusual rheological behavior: the minimum viscosity does not occur as expected at [Formula: see text], but instead decreases with further increase of [Formula: see text] to [Formula: see text]. The second normal stress difference [Formula: see text] acts similarly. This behavior is caused by particles ordering into a layered structure, as is also reflected by the zero slope with respect to time of the mean-square displacement in the velocity gradient direction. The relative viscosity [Formula: see text] of bidisperse rate-dependent suspensions can be predicted by a power law linking it to [Formula: see text], [Formula: see text] in both low and high shear stress regimes. The agreement between the power law and experimental data from literature demonstrates that the model captures well the effect of particle size distribution, showing that viscosity roughly collapses onto a single master curve when plotted against the reduced volume fraction [Formula: see text]. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email