DIELECTROPHORETIC ASSEMBLY OF COLLOIDS IN TOGGLED AC FIELDS
Date
2017-05
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
The dielectrophoretic directed self-assembly of colloidal particles is a rapid, tunable,
and simple method for the production of materials with phononic and photonic
band gaps. However, under the application of a constant AC electric fi eld, particles
become kinetically trapped in non-equilibrium structures containing numerous defects
which interfere with the desired phononic and photonic properties. This problem is
ampli ed by anisotropic particles as they must translationally and rotationally align
to assemble into equilibrium structues. To resolve this limitation of dielectrophoretic
self-assembly, a method to anneal kinetically trapped con gurations to an equilibrium
state is needed.
Before exploring an approach to improve the order of structures formed by dielectrophoretic directed self-assembly, a well-documented method for producing planar
electrodes, and their use in the construction of a dielectrophoretic sample cell is presented.
Furthermore, the high voltage circuit used to generate the applied AC electric
fi eld is introduced and thoroughly characterized.
This experimental setup is then used to investigate the use of toggled AC electric
elds to assemble polystyrene colloids into crystalline structures free of defects. The
time evolution of the macroscopic structures and the long-time microscopic structures
formed under the influence of toggled AC electric fi elds are discussed for three colloidal
suspensions: 1 m polystyrene spheres dispersed in a density mismatched H2O-based
medium, in a density matched H2O/D2O-based medium, and polystyrene dicolloids
in a density mismatched H2O-based medium. The rst of these suspensions suggests
toggling is not necessary to construct equilibrium structures from isotropic particles
with weak interactions. When the 1 m particles are suspended in a density matched
solution, only localized ordering is observed indicating gravity is an integral force in
the formation of macroscopic colloidal crystals through dielectrophoretic self-assembly.
Finally, the dicolloidal suspension exhibits an increase in order when a toggled eld is
applied at a frequency of 0.1 Hz rather than a constant eld. This suggests toggled
elds make it possible to improve the order of these particles, which are particular
difficult to assemble due to their anisotropy.
Description
Keywords
Chemical Engineering, DIELECTROPHORETIC, COLLOIDS, AC FIELDS