Particle Clustering and Pattern Formation during Electrophoretic Deposition:  A Hydrodynamic Model

Abstract

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.

Electrochemical Polarization-Induced Changes in the Growth of Individual Cells and Biofilms of Pseudomonas fluorescens (ATCC 17552)

“…7b). The maximum thickness observed at this potential was 16 Ϯ 2 m. The changes in microcolony features and distribution can be explained if the synergic influence of the modified growth of individual cells, the electrophoretic effects on charged bacteria, and the electro-osmotic induction of cell clustering (2,13,15) is considered. All these processes are thought to contribute to the formation of tightly packed microcolonies under positive polarization ( Fig.…”

Colloidal electroconvection in a thin horizontal cell. II. Bulk electroconvection of water during parallel-plate electrolysis

“…[1][2][3] These flows exert hydrodynamic forces on the spheres, and their motions, in turn, redirect the flows. [2][3][4][5] We previously reported 6,7 that the interplay of microscopic electrohydrodynamic flows around individual spheres can give rise to large-scale convective instabilities characterized by highly organized flow patterns involving thousands of spheres. These colloidal electroconvective patterns form at biases just above the threshold for steady electrolysis, and their structure depends on the properties and concentration of the colloidal spheres.…”

Dynamic Self-Assembly and Patterns in Electrostatically Driven Granular Media

“…Phase transitions and clustering instability of the electrostatically driven granular gas were found. The studies of self-assembly of colloidal particles in aqueous solutions revealed the importance of self-induced electrohydrodynamic (EHD) convective flows on the formation of various precipitate states [4,7,8,9,10]. Ordered clusters of particles vibrated in liquid were studied in Ref.…”