Rapid Brownian and Gravitational Coagulation

The influence of a high electric field applied on both fluid flow and particle velocities is quantified at large Peclet numbers. The experiments involved simultaneous particle image velocimetry and flow rate measurements. These are conducted in polydimethylsiloxane channels with spherical nonconducting polystyrene particles and DI water as the background flow. The high electric field tests produced up to three orders of magnitude higher electrokinetic velocities than any previous reports. The maximum electroosmotic velocity and electrophoretic velocity measured were 3.55 and 2.3 m/s. Electrophoretic velocities are measured over the range of 100 V/cm < E < 250 000 V/cm. The results are separated according to the different nonlinear theoretical models, including low and high Peclet numbers, and weak and strong concentration polarization. They show good agreement with the models. Such fast velocities could be used for flow separation, mixing, transport, control, and manipulation of suspended particles as well as microthrust generation among other applications.

Section: Introductionmentioning

confidence: 84%

E^{^{3} /_{2}}

. In the case of strong concentration polarization, due to the complexity of the phenomena, an analytical solution is only available for the electroosmotic velocity.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast electrokinetics

Youssefi

Díez

2016

“…If the thickness of the double layer surrounding a particle is comparable to its linear size, then its diffusiophoretic behavior is governed mainly by two locally induced electric fields, E DLP and E diffusivity . The former comes from the asymmetry of the double layer, known as chemiphoresis or double‐layer polarization (DLP).…”

Section: Introductionmentioning

confidence: 99%

“…Two types of DLP are present: type I DLP occurs inside the double layer, yielding a local electric field E DLPI , driving the particle toward the high concentration side, and type II DLP occurs immediately outside the double layer, yielding a local electric field E DLPII , driving the particle toward the low concentration side , , , . E diffusivity is the background electric field coming from the difference in ionic diffusivities , , , , . Note that because a charged particle is surrounded by a double layer, which is rich in counterions, E DLPI , E DLPII , and E diffusivity , all drive the nearby fluid to flow in a direction opposite to the direction of diffusiophoresis, yielding hydrodynamic retardation forces acting on the particle.…”

Section: Introductionmentioning

confidence: 99%

Diffusiophoresis of a polyelectrolyte in a salt concentration gradient

Liu

Hsu

et al. 2012

The diffusiophoresis of a polyelectrolyte subject to an applied salt concentration gradient is modeled theoretically. The entirely porous type of particle is capable of simulating entities such as DNA, protein, and synthetic polymeric particles. The dependence of the diffusiophoretic behavior of the polyelectrolyte on its physical properties, and the types of ionic species and their bulk concentrations are discussed in detail. We show that in addition to the effects coming from the polarization of double layer and the difference in the ionic diffusivities, the polarization of the condensed counterions inside the polyelectrolyte might also be significant. The last effect, which has not been reported previously, reduces both the electric force and the hydrodynamic force acting on the polyelectrolyte. Both the direction and the magnitude of the diffusiophoretic velocity of the polyelectrolyte are found to highly depend upon its physical properties. These results provide valuable references for applications such as DNA sequencing and catalytic nano- or micromotors.

“…For the last 60 years, since the pioneering contribution of Levich , most studies on induced‐charge electrokinetics of polarizable particles have dealt with homogeneous (mainly spherical) geometries. In this context, we mention the seminal contributions of the Ukrainian school and the more recent works by Squires and Bazant . The nonlinear electrokinetic phenomena described are currently widely used in various branches of modern nano/microtechnologies and microfluidic devices to drive, separate, and manipulate both latex and metallic colloids.…”

Section: Introductionmentioning

confidence: 99%

Dipolophoresis of Janus nanoparticles in a microchannel

Miloh

2013

A nonlinear dipolophoretic analysis is applied to analytically explain the counterintuitive experimental results of Gangwal et al. that an uncharged micro/nanosize dielectric Janus particle is attracted to the wall of a microchannel when exposed to an AC-uniform electric field in the direction parallel to the no-slip boundaries. We employ the so-called "weak" field assumption and consider a metallodielectric Janus colloid comprising two semispheres of distinct dielectric properties subject to an oscillating-uniform electric field with moderate frequency (below the Maxwell-Wagner limit). The Debye scale (ratio of electric double layer thickness to particle size) is considered unrestricted. Under the low Reynolds number hypothesis, Faxén's theorem and the Green's function (Stokeslet) method of singularities, including appropriate images with respect to the no-slip boundary, are applied under the remote-field approximation to determine the dynamics and trajectory of a small colloid moving near a wall. When assuming maximum dielectric contrasts between hemispheres and relatively low Debye scale (compared to particle radius), a rather simple relation for the equilibrium position of the colloid (i.e. tilt angle and distance from the wall) is obtained and found to be in qualitative good agreement with the experimental observations of Gangwal et al. and the predictions of Kilic and Bazant.