pH-Responsive Microrods Produced by Electric-Field-Induced Aggregation of Colloidal Particles

2007 ◽  
Vol 19 (11) ◽  
pp. 1523-1527 ◽  
Author(s):  
D. R. E. Snoswell ◽  
R. K. Brill ◽  
B. Vincent
Keyword(s):  
Electric Field ◽  
Colloidal Particles ◽  
Ph Responsive ◽  
Induced Aggregation

Assembly of Colloidal Particles into Microwires Using an Alternating Electric Field

Langmuir ◽  
2005 ◽  
Vol 21 (11) ◽  
pp. 4874-4880 ◽  
Author(s):  
Simon O. Lumsdon ◽  
David M. Scott
Keyword(s):  
Electric Field ◽  
Colloidal Particles ◽  
Alternating Electric Field

scholarly journals Bidirectional rotation control of a carbon fiber in nematic liquid crystal using AC electric field

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Jun-Yong Lee ◽  
Jeong-Seon Yu ◽  
Jong-Hyun Kim
Keyword(s):  
Free Energy ◽  
Liquid Crystal ◽  
Electric Field ◽  
Colloidal Particles ◽  
Colloidal System ◽  
Wide Angle ◽  
Local Minima ◽  
Free Energies ◽  
Rotation Direction ◽  
Ac Electric Field

Abstract Colloidal particles dispersed in nematic liquid crystals are aligned along the orientation that minimizes the elastic free energy. Through applying an electric field to a nematic colloidal system, the orientation of the director can change. Consequently, colloidal particles realign to minimize the total free energy, which is the sum of the elastic and electric free energies. Herein, we demonstrate that if the preferred rotation directions given by the electric and elastic free energies are different during realignment, the rotation direction of the particle can be controlled by how we apply the electric field. When the strength of the electric field gradually increases, the particles rotate in the same direction as the rotation of the director. However, when a sufficiently high electric field is suddenly applied, the particles rotate in the opposite direction. In this study, we analyzed the effect of free energy on the bidirectional rotation behavior of the particles using a theoretical model. This study provides an effective approach to control the rotational behavior of colloidal particles over a wide-angle range between two orientational local minima.

Using Shear and DC Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

2014 ◽  
Author(s):  
Minami Yoda ◽  
Necmettin Cevheri
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Poiseuille Flow ◽  
Lift Force ◽  
Colloidal Particles ◽  
Solid Surfaces ◽  
Electric Field Magnitude ◽  
Field Magnitude ◽  
Combined Flow ◽  
Lift Forces

Manipulating suspended neutrally buoyant colloidal particles of radii a = O(0.1 μm–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the DLVO theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ̇ near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125 nm–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ̇, a scaling consistent with hydrodynamic, vs. electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field or in Poiseuille flow for the same γ̇. Initial results also imply that this force, when repulsive, scales as γ̇1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

Dielectrophoretic Mixing With Novel Electrode Geometry

2009 ◽  
Author(s):  
G. Naga Siva Kumar ◽  
Sushanta K. Mitra ◽  
Subir Bhattacharjee
Keyword(s):  
Electric Field ◽  
Cell Activation ◽  
Colloidal Particles ◽  
Colloidal Suspension ◽  
Three Dimensional ◽  
Colloidal Suspensions ◽  
Navier Stokes ◽  
Mixing Efficiency ◽  
Computational Domain ◽  
Element Analysis

Electrokinetic mixing of analytes at micro-scale is important in several biochemical applications like cell activation, DNA hybridization, protein folding, immunoassays and enzyme reactions. This paper deals with the modeling and numerical simulation of micromixing of two different types of colloidal suspensions based on principle of dielectrophoresis (DEP). A mathematical model is developed based on Laplace, Navier-Stokes, and convection-diffusion-migration equations to calculate electric field, velocity, and concentration distributions, respectively. Mixing of two colloidal suspensions is simulated in a three-dimensional computational domain using finite element analysis considering dielectrophoretic, gravitational and convective (advective)–diffusive forces. Phase shifted AC signal is applied to the alternating electrodes for achieving the mixing of two different colloidal suspensions. The results indicate that the electric field and DEP forces are maximum at the edges of the electrodes and become minimum elsewhere. As compared to curved edges, straight edges of electrodes have lower electric field and DEP forces. The results also indicate that DEP force decays exponentially along the height of the channel. The effect of DEP forces on the concentration profile is studied. It is observed that, the concentration of colloidal particles at the electrodes edges is very less compared to elsewhere. Mixing of two colloidal suspensions due to diffusion is observed at the interface of the two suspensions. The improvement in mixing after applying the repulsive DEP forces on the colloidal suspension is observed. Most of the mixing takes place across the slant edges of the triangular electrodes. The effect of electrode pairs and the mixing length on degree of mixing efficiency are also observed.

Electric field induced charging of colloidal particles in a nonpolar liquid

2018 ◽  
Vol 515 ◽  
pp. 248-254 ◽  
Author(s):  
Caspar Schreuer ◽  
Stijn Vandewiele ◽  
Filip Strubbe ◽  
Kristiaan Neyts ◽  
Filip Beunis
Keyword(s):  
Electric Field ◽  
Colloidal Particles ◽  
Nonpolar Liquid

Numerical Study on Electrokinetic Interaction Between a Pair of Cylindrical Colloidal Particles

2009 ◽  
Author(s):  
Dolfred Vijay Fernandes ◽  
Sangmo Kang ◽  
Yong Kweon Suh
Keyword(s):  
Flow Field ◽  
Electric Field ◽  
Colloidal Particles ◽  
Stokes Equations ◽  
Separation Efficiency ◽  
Numerical Study ◽  
Interaction Force ◽  
Surface Element ◽  
Immersed Boundary ◽  
Interaction Forces

Electrophoresis is the motion of dispersed particles relative to a fluid under the influence of an electric field. Presently this phenomenon of electrokinetics is widely used in biotechnology for the separation of proteins, sequencing of polypeptide chains etc. The separation efficiency of these biomolecules is affected by their aggregation. Thus it is important to study the interaction forces between the molecules. In this study we calculate the electrophoretic motion of a pair of colloidal particles under axial electric field. The hydrodynamic and electric double layer (EDL) interaction forces are calculated numerically. The EDL interaction force is calculated from electric field distribution around the particle using Maxwell stress tensor and the hydrodynamic force is calculated from the flow field obtained from the solution of Stokes equations. The continuous forcing approach of immersed boundary method is used to obtain flow field around the moving particles. The EDL distribution around the particles is obtained by solving Poisson-Nernst-Planck (PNP) equations on a hybrid grid system. The EDL interaction force calculated from numerical solution is compared with the one obtained from surface element integration (SEI) method.

Using Shear and Direct Current Electric Fields to Manipulate and Self-Assemble Dielectric Particles on Microchannel Walls

2014 ◽  
Vol 5 (3) ◽  
Author(s):  
Necmettin Cevheri ◽  
Minami Yoda
Keyword(s):  
Electric Field ◽  
Electric Fields ◽  
Poiseuille Flow ◽  
Lift Force ◽  
Colloidal Particles ◽  
Solid Surfaces ◽  
Electric Field Magnitude ◽  
Field Magnitude ◽  
Combined Flow ◽  
Lift Forces

Manipulating suspended neutrally buoyant colloidal particles of radii a = O (0.1–1 μm) near solid surfaces, or walls, is a key technology in various microfluidics devices. These particles, suspended in an aqueous solution at rest near a solid surface, or wall, are subject to wall-normal “lift” forces described by the Derjaguin–Landau–Verwey–Overbeek (DLVO) theory of colloid science. The particles experience additional lift forces, however, when suspended in a flowing solution. A fundamental understanding of such lift forces could therefore lead to new methods for the transport and self-assembly of particles near and on solid surfaces. Various studies have reported repulsive electroviscous and hydrodynamic lift forces on colloidal particles in Poiseuille flow (with a constant shear rate γ· near the wall) driven by a pressure gradient. A few studies have also observed repulsive dielectrophoretic-like lift forces in electroosmotic (EO) flows driven by electric fields. Recently, evanescent-wave particle tracking has been used to quantify near-wall lift forces on a = 125–245 nm polystyrene (PS) particles suspended in a monovalent electrolyte solution in EO flow, Poiseuille flow, and combined Poiseuille and EO flow through ∼30 μm deep fused-silica channels. In Poiseuille flow, the repulsive lift force appears to be proportional to γ·, a scaling consistent with hydrodynamic, versus electroviscous, lift. In combined Poiseuille and EO flow, the lift forces can be repulsive or attractive, depending upon whether the EO flow is in the same or opposite direction as the Poiseuille flow, respectively. The magnitude of the force appears to be proportional to the electric field magnitude. Moreover, the force in combined flow exceeds the sum of the forces observed in EO flow for the same electric field and in Poiseuille flow for the same γ·. Initial results also imply that this force, when repulsive, scales as γ·1/2. These results suggest that the lift force in combined flow is fundamentally different from electroviscous, hydrodynamic, or dielectrophoretic-like lift. Moreover, for the case when the EO flow opposes the Poiseuille flow, the particles self-assemble into dense stable periodic streamwise bands with an average width of ∼6 μm and a spacing of 2–4 times the band width when the electric field magnitude exceeds a threshold value. These results are described and reviewed here.

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