scholarly journals Light-induced manipulation of passive and active microparticles

2021 ◽  
Vol 44 (4) ◽  
Author(s):  
Pooja Arya ◽  
Maren Umlandt ◽  
Joachim Jelken ◽  
David Feldmann ◽  
Nino Lomadze ◽  
...  
Keyword(s):  
Steady State ◽  
Colloidal Particles ◽  
Solid Wall ◽  
Ionic Surfactants ◽  
Concentration Gradients ◽  
Profile Shape ◽  
Osmotic Flow ◽  
Flow Generation ◽  
Controlled Flow ◽  
Shape And Size

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

Diffusiophoresis in ionic surfactants: effect of micelle formation

Soft Matter ◽  
2019 ◽  
Vol 15 (2) ◽  
pp. 278-288 ◽  
Author(s):  
Patrick B. Warren ◽  
Sangwoo Shin ◽  
Howard A. Stone
Keyword(s):  
Self Assembly ◽  
Surfactant Concentration ◽  
Colloidal Particles ◽  
Micelle Formation ◽  
Ionic Surfactants ◽  
Ionic Surfactant ◽  
Association Model ◽  
Concentration Gradients ◽  
Chemical Association

We explore the consequences of micelle formation for diffusiophoresis of charged colloidal particles in ionic surfactant concentration gradients, using a quasi-chemical association model for surfactant self assembly.

Non-steady state behaviour of heavy metals in contaminated freshwater sediments

1998 ◽  
Vol 37 (6-7) ◽  
pp. 39-46 ◽  
Author(s):  
Gerard A. van den Berg ◽  
J. P. Gustav Loch ◽  
John J. G. Zwolsman ◽  
Lambertus M. van der Heijdt
Keyword(s):  
Heavy Metals ◽  
Heavy Metal ◽  
Steady State ◽  
Surface Water ◽  
Metal Mobility ◽  
Pore Waters ◽  
Concentration Gradients ◽  
River Meuse ◽  
State Behaviour ◽  
Diffusive Fluxes

The behaviour of heavy metals has been investigated in contaminated sediments of the river Meuse, The Netherlands. Due to temporal changes in temperature and degradability of organic matter, the depths of the redox boundaries fluctuate. This contributes to a non-steady state. As a result of oxidation processes, a distinct peak in heavy metal concentrations in pore water is measured at the sediment-water interface. Because the studied anoxic sediments contain low levels of sulphide, other solid phases are expected to be of importance in the binding of heavy metals. Furthermore, heterogeneity of the sediment and complexation with dissolved organic compounds may result in supersaturation of the anoxic pore waters with respect to discrete heavy metal sulphides, thus influencing heavy metal mobility. Calculations using concentration gradients of heavy metals indicate that diffusive fluxes between the sediment and the surface water contribute to concentrations in the surface water, although significant effects may be confined to specific locations.

Energetics of sugar transport by isolated intestinal epithelial cells: effects of cytochalasin B

1979 ◽  
Vol 237 (1) ◽  
pp. C56-C63 ◽  
Author(s):  
G. A. Kimmich ◽  
J. Randles
Keyword(s):  
Steady State ◽  
Epithelial Cells ◽  
Transport System ◽  
Cytochalasin B ◽  
Intestinal Epithelial Cells ◽  
Sugar Accumulation ◽  
Facilitated Diffusion ◽  
Intestinal Epithelial ◽  
Passive System ◽  
Concentration Gradients

The capability of isolated intestinal epithelial cells to establish concentration gradients of 3-O-methylglucose (3-OMG) by a Na+-dependent transport system is limited by concomitant function of a Na+-independent, facilitated diffusion transport system. Monosaccharides accumulated by the active system are continuously lost via the passive system, which acts to lower steady-state sugar gradients maintained by the cell. Cytochalasin B is a potent inhibitor of the passive system and allows the cells to establish a sugar gradient that is much higher than normal. When extracellular [3-;OMG] is 1 mM, cytochalasin induces sugar accumulation ratios of 30-;fold (+/- phlorizin) in contrast to control ratios of approximately 10-;fold. When [3-;OMG] is 0.1 mM, cytochalasin (0.1 mM) induces 40-;fold accumulation ratios. When changes in extracellular sugar concentration are considered, steady-state concentration gradients observed are 70-;fold. For a Na:sugar coupling stoichiometry of 1:1, gradients of this magnitude represent the approximate theoretical maximum for a transport system driven exclusively by the transmembrane electrochemical potential for Na+.

Osmosis in small pores: a molecular dynamics study of the mechanism of solvent transport

2005 ◽  
Vol 461 (2053) ◽  
pp. 273-296 ◽  
Author(s):  
K. S. Kim ◽  
I. S. Davis ◽  
P. A. Macpherson ◽  
T. J. Pedley ◽  
A. E. Hill
Keyword(s):  
Molecular Dynamics ◽  
Flow Rate ◽  
Low Flow ◽  
Transport Parameters ◽  
Concentration Gradients ◽  
Cylindrical Pore ◽  
Osmotic Flow ◽  
Energy Gradient ◽  
Pressure Flows ◽  
Asymmetric Pores

Osmosis through semi–permeable pores is a complex process by which solvent is driven by its free energy gradient towards a solute–rich reservoir. We have studied osmotic flow across a semi–permeable cylindrical pore using hard–sphere molecular dynamics which simulates osmosis in the absence of attractive forces between solute and solvent. In addition, we recorded the rates of pressure–driven solvent flow and the diffusive flow of labelled solvent under concentration gradients. It is apparent that there are differences, which are radius dependent, between viscous and diffusive solvent permeabilities in small pores. The osmotic flow rate is decreased by allowing solute entry into part of the pore, an effect which is not due to solute obstruction. The flow rate is dependent on the structure of the pore, which for asymmetric pores leads, surprisingly, to flow asymmetry or osmotic rectification. In the absence of any possible viscous rectification at these very low flow rates the effect correlates with changes between diffusive and pressure flows created by the presence of solute, an effect which has been predicted from thermodynamic arguments. The geometry of a semi–permeable pore in relation to the solute size is therefore required to predict the osmotic flow rate, a departure from the classical picture. Finally, by extracting transport parameters from simulations with pure solvent, we examine the departure of observed flow rate from that predicted by continuum mechanics, obtaining drag coefficients which we compare with those derived from hydrodynamics alone.

A macrotransport equation for the particle distribution in the flow of a concentrated, non-colloidal suspension through a circular tube

2013 ◽  
Vol 734 ◽  
pp. 219-252 ◽  
Author(s):  
Arun Ramachandran
Keyword(s):  
Cross Section ◽  
Colloidal Particles ◽  
Particle Distribution ◽  
Circular Tube ◽  
Colloidal Suspension ◽  
Classical Problem ◽  
Taylor Dispersion ◽  
Concentration Gradients ◽  
Concentrated Suspension ◽  
The Cross

AbstractA two-time-scale perturbation expansion is used to derive a cross-section-averaged convection–dispersion equation for the particle distribution in the flow of a concentrated suspension of neutrally buoyant, non-colloidal particles through a straight, circular tube. Since the cross-streamline motion of particles is governed by shear-induced migration, the Taylor-dispersion coefficient ${\mathscr{D}}_{eff} $ scales as ${U}^{\prime } {R}^{3} / {a}^{2} $, ${U}^{\prime } $, $R$ and $a$ being the characteristic velocity scale, the tube radius and the particle radius, respectively. Here ${\mathscr{D}}_{eff} $ is found to decrease monotonically with an increase in the particle concentration. The linear dependence of ${\mathscr{D}}_{eff} $ on ${U}^{\prime } $ implies that changes in the cross-section averaged axial concentration profile are dependent only on the total axial strain experienced by the suspension. This stipulates that the spatial evolution of a fluctuation in the concentration of particles in the flowing suspension, or the width of the mixing zone between two regions of different concentrations in the tube will be independent of the suspension velocity in the tube. A second interesting feature in particulate dispersion is that the effective velocity of the particulate phase is concentration-dependent, which, by itself (i.e. without considering Taylor dispersion), can produce either sharpening or relaxation of concentration gradients. In particular, shocks with positive concentration gradients along the flow direction can asymptotically evolve into time-independent distributions in an appropriately chosen frame of reference, and concentration pulses relax asymmetrically. These trends are contrasted with those expected from the classical problem of Taylor dispersion of a passive tracer in the same geometry. The results in this paper are especially relevant for suspension flows through microfluidic geometries, where the induction lengths for shear-induced migration are short.

Experimental Investigation on the Electrokinetic Motions of Colloidal Particles at an Interfacial Boundary Between Solid and Liquid

2019 ◽  
Author(s):  
Katsuaki Shirai ◽  
Shoichiro Kaji ◽  
Shigeo Hosokawa ◽  
Tsuyoshi Kawanami ◽  
Shigeki Hirasawa
Keyword(s):  
Heat Transfer ◽  
Experimental Investigation ◽  
Electric Fields ◽  
Spatial Resolution ◽  
Measurement System ◽  
Colloidal Particles ◽  
Solid Wall ◽  
Wall Region ◽  
And Performance ◽  
Solid Liquid

Abstract We investigate electrokinetic behavior of colloidal particles in the vicinity of a solid-liquid interface. Colloidal liquids are expected to be used as thermal transport media for heat transfer applications such as nanofluids and phase change emulsions. They contain submicrometer-sized particles in liquid, and electrokinetic behavior of the solute particles should play an important role in the heat transfer between solid-liquid interfacing boundaries. However, experimental investigation of the behavior remains difficult due to the required spatial resolution beyond diffraction limit. We developed a measurement system based on laser Doppler principle using an interference of evanescent waves generated at total internal reflections of incident lasers at a solid wall. The system was developed for the measurement of velocities of colloidal particles at an interfacing boundary of colloidal liquid and a solid wall. The system has a unique advantage of a high spatial resolution in the direction perpendicular to the boundary due to the short penetration depth of an evanescent wave in the range of a few hundred nanometers. The principle and performance of the measurement system were investigated using a scanning probe in the measurement volume. We experimentally confirmed the validity of the measurement and characterized the uncertainty of velocity measurement. The system was further applied in a series of measurements of alumina particles dispersed in water in a square-shaped cell under induced electric fields. The measured velocities are proportional to the field strengths at different particle concentrations. The linear relationship is consistent with theoretical predictions, which demonstrates the feasibility of the system for the measurement of velocities of colloidal particles in the near wall region.

scholarly journals Preferential Pathways for Fluid and Solutes in Heterogeneous Groundwater Systems: Self-Organization, Entropy, Work

2021 ◽  
Author(s):  
Erwin Zehe ◽  
Ralf Loritz ◽  
Yaniv Edery ◽  
Brian Berkowitz
Keyword(s):  
Fluid Flow ◽  
Steady State ◽  
Hydraulic Conductivity ◽  
Solute Transport ◽  
Energy Input ◽  
Self Organization ◽  
Saturated Porous Media ◽  
Concentration Gradients ◽  
Transport Pathways ◽  
Preferential Pathways

Abstract. Patterns of distinct preferential pathways for fluid flow and solute transport are ubiquitous in heterogeneous, saturated and partially saturated porous media. Yet, the underlying reasons for their emergence, and their characterization and quantification, remain enigmatic. Here we analyze simulations of steady state fluid flow and solute transport in two-dimensional, heterogeneous saturated porous media with a relatively short correlation length. We demonstrate that the downstream concentration of solutes in preferential pathways implies a downstream declining entropy in the transverse distribution of solute transport pathways. This reflects the associated formation and downstream steepening of a concentration gradient transversal to the main flow direction. With an increasing variance of the hydraulic conductivity field, stronger transversal concentration gradients emerge, which is reflected in an even smaller entropy of the transversal distribution of transport pathways. By defining "self-organization" through a reduction in entropy (compared to its maximum), our findings suggest that a higher variance and thus randomness of the hydraulic conductivity coincides with stronger macroscale self-organization of transport pathways. While this finding appears at first sight striking, it can be explained by recognizing that emergence of spatial self-organization requires, in light of the second law of thermodynamics, that work be performed to establish transversal concentration gradients. The emergence of steeper concentration gradients requires that even more work be performed, with an even higher energy input into an open system. Consistently, we find that the energy input necessary to sustain steady-state fluid flow and tracer transport grows with the variance of the hydraulic conductivity field as well. Solute particles prefer to move through pathways of very high power, and these pathways pass through bottlenecks of low hydraulic conductivity. This is because power depends on the squared spatial head gradient, which is in these simulations largest in regions of low hydraulic conductivity.

Sign in / Sign up

Export Citation Format

Share Document