Academic literature on the topic 'Diffusio-Osmotic'

Diffusion of colloidal particles in microchannels has been extensively investigated, where the channel wall is either a no-slip or a slip-passive boundary. However, in the context of active fluids, driving boundary walls are ubiquitous and are expected to have a substantial effect on the particle dynamics. By mesoscale simulations, we study the diffusion of a chemically active colloidal particle in composite channels, which are constructed by alternately arranging the no-slip and diffusio-osmotic boundary walls. In this case, the chemical reaction catalyzed by the active colloidal particle creates a local chemical gradient along the channel wall, which drives a diffusio-osmotic flow parallel to the wall. We show that the diffusio-osmotic flow can significantly change the spatial distribution and diffusion dynamics of the colloidal particle in the composite channels. By modulating the surface properties of the channel wall, we can achieve different patterns of colloidal position distribution. The findings thus propose a novel possibility to manipulate colloidal diffusion in microfluidics, and highlight the importance of driving boundary walls in dynamics of colloidal particles in microchannels.

Flow control is a highly relevant topic for micromanipulation of colloidal particles in microfluidic applications. Here, we report on a system that combines two-surface bound flows emanating from thermo-osmotic and diffusio-osmotic mechanisms. These opposing flows are generated at a gold surface immersed into an aqueous solution containing a photo-sensitive surfactant, which is irradiated by a focused UV laser beam. At low power of incoming light, diffusio-osmotic flow due to local photo-isomerization of the surfactant dominates, resulting in a flow pattern oriented away from the irradiated area. In contrast, thermo-osmotic flow takes over due to local heating of the gold surface at larger power, consequently inducing a flow pointing toward the hotspot. In this way, this system allows one to reversibly switch from outward to inward liquid flow with an intermittent range of zero flow at which tracer particles undergo thermal motion by just tuning the laser intensity only. Our work, thus, demonstrates an optofluidic system for flow generation with a high degree of controllability that is necessary to transport particles precisely to desired locations, thereby opening innovative possibilities to generate advanced microfluidic applications.

We employ the moderate-Péclet-number macroscale model developed in part 2 of this sequence (Schnitzer et al., J. Fluid Mech., vol. 704, 2012, pp. 109–136) towards the calculation of electroviscous forces on charged solid particles engendered by an imposed relative motion between these particles and the electrolyte solution in which they are suspended. In particular, we are interested in the kinematic irreversibility of these forces, stemming from the diffusio-osmotic slip which accompanies the salt-concentration polarisation induced by that imposed motion. We illustrate the electroviscous irreversibility using two prototypic problems, one involving side-by-side sedimentation of two spherical particles, and the other involving a force-free spherical particle suspended in the vicinity of a planar wall and exposed to a simple shear flow. We focus on the pertinent limit of near-contact configurations, where use of lubrication approximations provides closed-form expressions for the leading-order lateral repulsion. In this approximation scheme, the need to solve the advection–diffusion equation governing the salt-concentration polarisation is circumvented.

An inhomogeneous catalyst surface leads to concentration gradients along this surface, which can generate diffusio-osmotic flows. The magnitude of this surface flow and the extent to which it impacts the...

The emergence of new nanoporous materials, based, e.g., on 2D materials, offers new avenues for water filtration and energy. There is, accordingly, a need to investigate the molecular mechanisms at the root of the advanced performances of these systems in terms of nanofluidic and ionic transport. In this work, we introduce a novel unified methodology for Non-Equilibrium classical Molecular Dynamic simulations (NEMD), allowing to apply likewise pressure, chemical potential, and voltage drops across nanoporous membranes and quantifying the resulting observables characterizing confined liquid transport under such external stimuli. We apply the NEMD methodology to study a new type of synthetic Carbon NanoMembranes (CNM), which have recently shown outstanding performances for desalination, keeping high water permeability while maintaining full salt rejection. The high water permeance of CNM, as measured experimentally, is shown to originate in prominent entrance effects associated with negligible friction inside the nanopore. Beyond, our methodology allows us to fully calculate the symmetric transport matrix and the cross-phenomena, such as electro-osmosis, diffusio-osmosis, and streaming currents. In particular, we predict a large diffusio-osmotic current across the CNM pore under a concentration gradient, despite the absence of surface charges. This suggests that CNMs are outstanding candidates as alternative, scalable membranes for osmotic energy harvesting.

Abstract We consider sedimented at a solid wall particles that are immersed in water containing small additives of photosensitive ionic surfactants. It is shown that illumination with an appropriate wavelength, a beam intensity profile, shape and size could lead to a variety of dynamic, both unsteady and steady state, configurations of particles. These dynamic, well-controlled and switchable particle patterns at the wall are due to an emerging diffusio-osmotic flow that takes its origin in the adjacent to the wall electrostatic diffuse layer, where the concentration gradients of surfactant are induced by light. The conventional nonporous particles are passive and can move only with already generated flow. However, porous colloids actively participate themselves in the flow generation mechanism at the wall, which also sets their interactions that can be very long ranged. This light-induced diffusio-osmosis opens novel avenues to manipulate colloidal particles and assemble them to various patterns. We show in particular how to create and split optically the confined regions of particles of tunable size and shape, where well-controlled flow-induced forces on the colloids could result in their crystalline packing, formation of dilute lattices of well-separated particles, and other states. Graphic Abstract

Pour lutter efficacement contre le réchauffement climatique, il est nécessaire d'augmenter la production d'énergies propres et renouvelables. L'énergie solaire, l'énergie éolienne, l’hydroélectrique et l'énergie marémotrice sont des technologies matures. L'augmentation de la production d'énergie renouvelable nécessite l'utilisation de sources d'énergie peu ou pas exploitées, comme l’énergie bleue. Cette forme d’énergie correspond à l’énergie générée lors du mélange d'eau douce et d'eau salée. Cependant, les procédés actuels d’extraction d'énergie à partir de gradients de sel restent inefficaces, principalement parce que les membranes sélectives commerciales sont peu performantes comme le cas de l’électrodialyse inverse ou l’Osmose à pression retardée qui ne sont toujours pas économiquement rentable. Les espoirs de membranes non sélectives dotées de canaux nanofluidiques chargés qui ont été conçus pour réduire la résistance interne de la cellule semblent être vains. Une nouvelle solution est proposée qui consiste à augmenter le potentiel de circuit ouvert de la membrane en y attachant des électrodes capacitives avec des groupements fonctionnels chargés négativement qui permet l’adsorption des ions, essentiellement les ions positifs. Une telle configuration nous permet de doubler le potentiel du circuit ouvert de la cellule sans trop modifier la résistance ohmique globale et donc de multiplier par 4 la puissance brute potentiellement récupérable.Après une étude approfondie réalisée dans le but de caractériser le procédé et une optimisation de la consommation énergique due aux pertes de charge, nous présentons un dispositif de quelques centimètres carrés avec une seule membrane récoltant une densité de puissance nette de 2 Watts par mètre carré de membrane (densité de puissance potentielle nette estimée à 5.4 W.m-2, ce qui rend le système économiquement viable
To effectively combat global warming, it is necessary to increase the production of clean, renewable energy. Solar, wind power, hydroelectric dams and tidal power plants are mature technologies. Increasing the production of this energy requires the use of energy sources that are little or not exploited like the blue energy which is the a less-known source with enormous potential that can be generated directly from the mixing of fresh and salt water. However, current processes for energy harvesting from salt gradients remain inefficient mainly because commercial selective membranes have poor performance as in the reverse electrodialysis or in the pressure retarded osmosis and still not economically viable. Hopes for nonselective membranes with charged nanofluidic channels which have been designed to reduce the internal resistance of the cell seem to be in vain. Here we present a novel solution that involves increasing the open circuit potential of the membrane by attaching tailored capacitive layers with negatively charged functional groups on the surface that adsorb ions, mainly the positive ones. Such a configuration allows us to double the potential of the open circuit of the cell without modifying too much the global ohmic resistance and thus to multiply by 4 the potentially recoverable power.After a thorough study carried out in order to characterize the process and an optimization of the energy consumption caused by the hydraulic pressure drop, we display a device of a few squared centimeters with only one membrane harvesting a net power density of 2 Watts per square meter of the membrane (estimated net potential power density 5.4 W.m−2 ) which makes the system economically viable