Berlin 2008 – scientific programme

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CPP: Fachverband Chemische Physik und Polymerphysik

CPP 20: POSTERS Driven Soft Matter

CPP 20.36: Poster

Wednesday, February 27, 2008, 16:00–18:30, Poster A

Colloids in AC fields: Edge localized instabilities in dielectrophoretic bottles — Jinyu Zhao, •Günter K. Auernhammer, and Doris Vollmer — MPI Polymerforschung, Mainz, Germany

Dielectric colloids dispersed in a dielectric liquid experience a body force in gradients of AC fields. This force is due to the contrast in the dielectric properties between the colloids and the surrounding liquid. It allows to tune the concentration of colloids in the dielectrophoretic bottle by changing the applied field.

We investigate the process of filling the dielectrophoretic bottle, i.e., directly after turning the field on. Our system consists of sterically stabilized PMMA colloids in a density-matching mixture of decaline and cyclohexyl bromide. At high frequencies of the applied field (100 kHz to 1MHz), we find that the spatially homogeneous migration of the colloids can be unstable against localized colloidal flows. Our experiments indicate a critical value of the driving force for the instability. The onset is at a field of ≈ 0.5 V/µ m in the dielectrophoretic bottle. We analyze this instability in analogy to the Rayleigh-Taylor instability. In contrast to the standard Rayleigh-Taylor instability, the driving body force is not due to gravity but due to the applied field gradient.