Self-assembly and vortices formed by microparticles in weak electrolytes.

We carried out experimental studies of the self-assembly of metallic micron-size particles in poorly conducting liquid subject to a constant electric field. Depending on the experimental conditions, the particles self-assemble into long chains directed along the electric field lines and form vortices and other structures. The vortices perform Brownian-type random motion due to self-induced chaotic hydrodynamic flows. We measured the diffusivity constant of the vortices and the conductivity and mechanical stiffness of the chains.

Dynamic self-assembly and patterns in electrostatically driven granular media.

We show that granular media, consisting of metallic microparticles immersed in a poorly conducting liquid in a strong dc electric field, self-assemble into a rich variety of novel phases. These phases include static precipitates: honeycombs and Wigner crystals; and novel dynamic condensates: toroidal vortices and pulsating rings. The observed structures are explained by the interplay between charged granular gas and electrohydrodynamic convective flows in the liquid.

Phase-sensitive detection in potential-modulated in situ absorption and probe beam deflection techniques: theoretical considerations.

A mathematical framework is presented for the quantitative analysis of in situ potential modulation spectroelectrochemical techniques based on phase-sensitive detection for the study of solution-phase redox systems under strict diffusion control. In the case of arrangements in which the probing beam is parallel to the electrode surface, the phase of the optical signal with respect to the applied potential, assuming negligible double-layer charging currents, was found to be proportional to y(omega/2D)(1/2), where y is the distance normal to the electrode, omega is the frequency of the perturbating signal, and D is the diffusion coefficient of the species responsible for absorption or refraction. Good agreement was found between theoretical predictions and the few available experimental results for both absorption and probe beam deflection-type experiments. In particular, in the case of solutions containing the chromophore trianisylamine and nonabsorbing p-benzoquinone, the phase angle difference between absorption and diffraction calculated from theory and measured experimentally yielded a common value of approximately 30 degrees.