8 research outputs found
Nonlinear electrophoresis of dielectric and metal spheres in a nematic liquid crystal
Electrophoresis is a motion of charged dispersed particles relative to a
fluid in a uniform electric field. The effect is widely used to separate
macromolecules, to assemble colloidal structures, to transport particles in
nano- and micro-fluidic devices and displays. Typically, the fluid is isotropic
(for example, water) and the electrophoretic velocity is linearly proportional
to the electric field. In linear electrophoresis, only a direct current (DC)
field can drive the particles. An alternate current (AC) field is more
desirable because it allows one to overcome problems such as electrolysis and
absence of steady flows. Here we show that when the electrophoresis is
performed in a nematic fluid, the effect becomes strongly non-linear with a
velocity component that is quadratic in the applied voltage and has a direction
that generally differs from the direction of linear velocity. The new
phenomenon is caused by distortions of the LC orientation around the particle
that break the fore-aft (or left-right) symmetry. The effect allows one to
transport both charged and neutral particles, even when the particles
themselves are perfectly symmetric (spherical), thus enabling new approaches in
display technologies, colloidal assembly, separation, microfluidic and
micromotor applications.Comment: 15 pages, 4 figure
Electrically Controlled Negative Refraction in a Nematic Liquid Crystal
The authors demonstrate electrically controlled negative refraction at the interface between an isotropic material and a uniaxial nematic liquid crystal, in which the optic axis is designed to make a large angle with the interface. Depending on the applied voltage, the refracted beam is either on the opposite side of the interface normal as compared to the incident beam (positive refraction) or on the same side (negative refraction).</p
Inelastic Collisions and Anisotropic Aggregation of Particles in a Nematic Collider Driven by Backflow
We design a nematic collider for controlled out-of-equilibrium anisotropic
aggregation of spherical colloidal particles. The nematic surrounding imparts
dipolar interactions among the spheres. A bidirectional backflow of the nematic
liquid crystal (NLC) in a periodic electric field forces the spheres to collide
with each other. The inelastic collisions are of two types, head-to-tail and
head-to-head. Head-to-tail collisions of dipoles result in longitudinal
aggregation while head-to-head collisions promote aggregation in the
transversal direction. The frequency of head-to-head collisions is set by the
impact parameter that allows one to control the resulting shape of aggregates,
their anisotropy and fractal dimension