Nonlinear Electrophoresis of Colloids Controlled by Anisotropic Conductivity and Permittivity of Liquid-Crystalline Electrolyte

Paladugu, Sathyanarayana; Conklin, Christopher; Viñals, Jorge; Lavrentovich, Oleg D.

doi:10.1103/physrevapplied.7.034033

Cited by 15 publications

(16 citation statements)

References 36 publications

(41 reference statements)

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“…4c,d essentially reverses the direction of the flow, confirming the observation that the velocity in LCEO should be proportional to the difference between these quantities at leading order [12]. This reversal is also in agreement with the recent experiments and 2D director-based numerical simulations [60] performed for a liquid crystal in which the sign of λ σ − λ ε can be reversed by a suitable choice of composition or temperature.…”

Section: Flow Profilesupporting

confidence: 89%

Q-tensor model for electrokinetics in nematic liquid crystals

et al. 2017

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We use a variational principle to derive a mathematical model for a nematic electrolyte in which the liquid crystalline component is described in terms of a second-rank order parameter tensor. The model extends the previously developed director-based theory and accounts for presence of disclinations and possible biaxiality. We verify the model by considering a simple but illustrative example of liquid crystal-enabled electro-osmotic flow around a stationary dielectric spherical particle placed at the center of a large cylindrical container filled with a nematic electrolyte. Assuming homeotropic anchoring of the nematic on the surface of the particle and uniform distribution of the director on the surface of the container, we consider two configurations with a disclination equatorial ring and with a hyperbolic hedgehog, respectively. The computed electro-osmotic flows show a strong dependence on the director configurations and on the anisotropies of dielectric permittivity and electric conductivity of the nematic, characteristic of liquid crystal-enabled electrokinetics. Further, the simulations demonstrate space charge separation around the dielectric sphere, even in the case of isotropic permittivity and conductivity. This is in agreement with the induced-charge electro-osmotic effect that occurs in an isotropic electrolyte when an applied field acts on the ionic charge it induces near a polarizable surface.

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Section: Flow Profilesupporting

confidence: 89%

Q-tensor model for electrokinetics in nematic liquid crystals

et al. 2017

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“…Rather, confinement effects in the third dimension may have to be resolved to provide even a qualitative understanding of flows and particle motion. Although we have generally found that the direction of the force of electrokinetic origin on a spatially fixed particle in two dimensions agrees with the observed direction of motion of free particles in a variety of experiments with similar parameter values [27,31,36], surprisingly, the observed electroosmotic flow around a particle, presented for example in Ref. [13], is qualitatively different than the two-dimensional numerical velocity field shown in Fig.…”

Section: Single Particle Electrokineticssupporting

confidence: 64%

“…The nematic is assumed to be a linear dielectric medium, with dielectric tensor ij = ⊥ δ ij + ∆ n i n j , with ∆ = − ⊥ , where and ⊥ are the dielectric constants parallel and perpendicular to n, respectively. Dielectric anisotropy reinforces or counteracts the effects introduced by mobility anisotropy in electrokinetic flows, leading to novel effects such as flow reversals upon composition or temperature changes of the nematic [27]. For reference, and when feasible, we retain both mobility and dielectric anisotropies in our approximate analytical calculations.…”

Section: Model and Configurations Of Interestmentioning

confidence: 99%

“…The electric potential and the normal component of the dielectric displacement are also continuous across the particle boundary. The experiments on particle transport involve particles with diameter 2R ∼ 5 − 50 µm placed in a cell of thickness h ∼ 50 − 100 µm and lateral size L ∼ 10 mm[13,27,31]. However, the patterned area with nonuniform director field is much smaller, a square of side a few hundred microns, up to a millimeter.…”

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confidence: 99%

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Electrokinetic effects in nematic suspensions: Single-particle electro-osmosis and interparticle interactions

et al. 2018

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Electrokinetic phenomena in a nematic suspension are considered when one or more dielectric particles are suspended in a liquid crystal matrix in its nematic phase. The long-range orientational order of the nematic constitutes a fluid with anisotropic properties. This anisotropy enables charge separation in the bulk under an applied electric field, and leads to streaming flows even when the applied field is oscillatory. In the cases considered, charge separation is seen to result from director field distortions in the matrix that are created by the suspended particles. We use a recently introduced electrokinetic model to study the motion of a single-particle hyperbolic hedgehog pair. We find this motion to be parallel to the defect-particle center axis, independent of field orientation. For a two-particle configuration, we find that the relative force of electrokinetic origin is attractive in the case of particles with perpendicular director anchoring, and repulsive for particles with tangential director anchoring. The study reveals large scale flow properties that are respectively derived from the topology of the configuration alone and from short scale hydrodynamics phenomena in the vicinity of the particle and defect.

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“…In ICEP, the structural dipole of Janus spheres can adopt any orientation perpendicular to the electric field and its trajectory is hard to control [10]. As will be shown below, the polarity of LCEP trajectories can be controlled by changing the anisotropy sign of conductivity and dielectric permittivity [36]. …”

Section: Lc-enabled Electrophoresismentioning

confidence: 99%

Liquid Crystals-Enabled AC Electrokinetics

Peng

Lavrentovich

2019

Micromachines

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Phenomena of electrically driven fluid flows, known as electro-osmosis, and particle transport in a liquid electrolyte, known as electrophoresis, collectively form a subject of electrokinetics. Electrokinetics shows a great potential in microscopic manipulation of matter for various scientific and technological applications. Electrokinetics is usually studied for isotropic electrolytes. Recently it has been demonstrated that replacement of an isotropic electrolyte with an anisotropic, or liquid crystal (LC), electrolyte, brings about entirely new mechanisms of spatial charge formation and electrokinetic effects. This review presents the main features of liquid crystal-enabled electrokinetics (LCEK) rooted in the field-assisted separation of electric charges at deformations of the director that describes local molecular orientation of the LC. Since the electric field separates the charges and then drives the charges, the resulting electro-osmotic and electrophoretic velocities grow as the square of the applied electric field. We describe a number of related phenomena, such as alternating current (AC) LC-enabled electrophoresis of colloidal solid particles and fluid droplets in uniform and spatially-patterned LCs, swarming of colloids guided by photoactivated surface patterns, control of LCEK polarity through the material properties of the LC electrolyte, LCEK-assisted mixing at microscale, separation and sorting of small particles. LC-enabled electrokinetics brings a new dimension to our ability to manipulate dynamics of matter at small scales and holds a major promise for future technologies of microfluidics, pumping, mixing, sensing, and diagnostics.

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Nonlinear Electrophoresis of Colloids Controlled by Anisotropic Conductivity and Permittivity of Liquid-Crystalline Electrolyte

Cited by 15 publications

References 36 publications

Q-tensor model for electrokinetics in nematic liquid crystals

Q-tensor model for electrokinetics in nematic liquid crystals

Electrokinetic effects in nematic suspensions: Single-particle electro-osmosis and interparticle interactions

Liquid Crystals-Enabled AC Electrokinetics

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