18 research outputs found
Drop Behavior in Uniform DC Electric Field
Drop deformation in uniform electric fields is a classic problem. The
pioneering work of G.I.Taylor demonstrated that for weakly conducting media,
the drop fluid undergoes a toroidal flow and the drop adopts a prolate or
oblate spheroidal shape, the flow and shape being axisymmetrically aligned with
the applied field. However, recent studies have revealed a nonaxisymmetric
rotational mode for drops of lower conductivity than the surrounding medium,
similar to the rotation of solid dielectric particles observed by Quincke in
the 19th century. This fluid dynamics video demonstrates three behavioral
modes. I) toroidal recirculation inside the drop in weak fields II)
nonaxisymmetric fluid rotation in strong fields and III) drop breakup in strong
fields.Comment: APS DFD Gallery of Fluid Motion 200
A Colloid Model System for Interfacial Sorption Kinetics
Particle
adsorption to an interface may be a complicated affair,
motivating detailed measurements of various processes involved, to
discover better understanding of the role of particle characteristics
and solution conditions on adsorption coverage and rate. Here we use
micron size colloids with a weak interfacial interaction potential
as a model system to track particle motion and measure the rates of
desorption and adsorption. The colloid-interface interaction strength
is tuned to be less than 10 <i>k</i><sub>B</sub><i>T</i> so that it is comparable to many nanoscale systems of
interest such as proteins at interfaces. The tuning is accomplished
using a combination of depletion, electrostatic, and gravitational
forces. The colloids transition between an entropically trapped adsorbed
state and a desorbed state through Brownian motion. Observations are
made using an light-emitting diode (LED)-based total internal reflection
microscopy (TIRM) setup. The observed adsorption and desorption rates
are compared to theoretical predictions based on the measured interaction
potential and near-wall particle diffusivity. The results demonstrate
that diffusion dynamics play a significant role when the barrier energy
is small. This experimental system will allow for the future study
of more complex dynamics such as nonspherical colloids and collective
effects at higher concentrations