29 research outputs found
Controlling the interfacial and bulk concentrations of spontaneously charged colloids in non-polar media
Stabilization and dispersion of electrical charge by colloids in non-polar
media, such as nano-particles or inverse micelles, is significant for a variety
of chemical and technological applications, ranging from drug delivery to
e-ink. Many applications require knowledge about concentrations near the
solid|liquid interface and the bulk, particularly in media where colloids
exhibit spontaneous charging properties. By modification of the mean field
equations to include the finite size effects that are typical in concentrated
electrolytes along with disproportionation kinetics, and by considering high
potentials, it is possible to evaluate the width of the condensed double layers
near planar electrodes and the bulk concentrations of colloids at steady state.
These quantities also provide an estimate of the minimum initial colloid
concentration that is required to support electroneutrality in the dispersion
bulk, and thus provide insights into the quasi-steady state currents that have
been observed in inverse micellar media.Comment: 13 pages, 5 figure
Front propagation and global bifurcations in a multi-variable reaction-diffusion model
We study the existence and stability of propagating fronts in Meinhardt's
reaction-diffusion model of branching in one spatial dimension. We identify a
saddle-node-infinite-period (SNIPER) bifurcation of fronts that leads to
episodic front propagation in the parameter region below propagation failure
and show that this state is stable. Stable constant speed fronts exist only
above this parameter value. We use numerical continuation to show that
propagation failure is a consequence of the presence of a T-point corresponding
to the formation of a heteroclinic cycle in a spatial dynamics description.
Additional T-points are identified that are responsible for a large
multiplicity of different traveling front-peak states. The results indicate
that multivariable models may support new types of behavior that are absent
from typical two-variable models but may nevertheless be important in
developmental processes such as branching and somitogenesis.Comment: 18 pages, 12 figure
Pattern formation aspects of electrically charged tri-stable media with implications to bulk heterojunction in organic photovoltaics
A common thread in designing electrochemically-based renewable energy devices
comprises materials that exploit nano-scale morphologies, e.g.,
supercapacitors, batteries, fuel cells, and bulk heterojunction organic
photovoltaics. In these devices, however, Coulomb forces often influence the
fine nano-details of the morphological structure of active layers leading to a
notorious decrease in performance. By focusing on bulk heterojunction organic
photovoltaics as a case model, a self-consistent mean-field framework that
combines binary (bi-stable) and ternary (tri-stable) morphologies with
electrokinetics is presented and analyzed, i.e., undertaking the coupling
between the spatiotemporal evolution of the material and charge dynamics along
with charge transfer at the device electrodes. Particularly, it is shown that
tri-stable composition may stabilize stripe morphology that is ideal bulk
heterojuction. Moreover, since the results rely on generic principles they are
expected to be applicable to a broad range of electrically charged
amphiphilic-type mixtures, such as emulsions, polyelectrolytes, and ionic
liquids.Comment: 8 pages, 4 figure