Clustering of latex particles 4−10 μm in diameter during and
after electrophoretic deposition of the
particles onto flat electrodes has been reported by Böhmer
(Langmuir
1996, 12, 5747). The
particles
interacted over length scales comparable to their size in the formative
stages of the clusters. Combinations
of two or more clusters already deposited approached each other to form
larger agglomerates. A model
based on electroosmotic flow about charged particles near surfaces is
developed here to explain these
observations. A charged, nonconducting particle near or on a flat
conducting surface creates flow in the
adjacent fluid due to electroosmosis about the particle's surface.
Fluid is drawn laterally toward the
particle near the electrode and pushed outward from the particle
farther away from the electrode above
the particle. Another particle near the electrode will be drawn
toward the central particle by this convection.
We first solve for the flow field about a single particle and then
compute the rearrangement of neighboring
particles in response to the flows. The clustering times for
different initial configurations of sets of particles
(e.g., regular versus irregular spacing) are calculated. The
average clustering times for irregular
configurations are greater than those for regular arrays. The
qualitative and quantitative features of the
experimental observations are captured by this model if the hindrance
effect of the solid wall is taken into
account. For example, the model correctly predicts the observed
declustering (separation) of particles
when the polarity of the electric field is reversed as well as the
observed cluster-to-cluster motion.
The motion of particles deposited on an electrode by electrophoresis is governed by electrokinetics, electrohydrodynamics, and Brownian diffusion. Under a dc electric field, the particles attract each other through their electroosmotic flows, but Brownian diffusion tends to randomize the distribution. Here, we develop a mathematical model for the time evolution of the probability of separation between two deposited particles. Predictions from the model for the mean separation versus time and the standard deviation about the mean separation are compared with experimental data for pairs of polystyrene latex particles deposited on thin-film metallic electrodes. The good agreement in the absence of adjustable parameters indicates that the convective-diffusion analysis based on electrokinetics is the mechanism behind particle aggregation during electrophoretic deposition under dc field conditions, that is, electroosmotic convection drives the particles together and the Brownian motion of the particles tends to separate them.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.