Berlin 2018 – wissenschaftliches Programm

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DY: Fachverband Dynamik und Statistische Physik

DY 68: Poster: Complex Fluids, Glasses, Granular

DY 68.8: Poster

Donnerstag, 15. März 2018, 15:30–18:00, Poster A

Electro-osmotic pumping for structured coatings — •raheema muhammad aslam, ran niu, and thomas palberg — Institute of Physics, JGU Mainz, Germany

We assemble charged colloidal spheres at deliberately chosen locations on a charged unstructured glass substrate utilizing ion exchange based micro-pumps. The pump uses trace amounts of ions to generate electroosmotic fluid flows. We show experimentally that our pump operates in almost deionized water for periods exceeding 24 h and induces fluid flows in micrometer per second over hundreds of micrometers. This flow displays a far-field, power-law decay which is characteristic of two-dimensional (2D) flow when the system is strongly confined and of three-dimensional (3D) flow when it is not. Experimentally, we systematically explore the control parameters of crystal assembly at and by micro-pumps and the mechanisms through which they depend on the experimental boundary conditions. We demonstrate that crystal quality depends crucially on the assembly distance of the colloids. This is understood as resulting from the competition between inward transport by the electro-osmotic pump flow and the electro-phoretic outward motion of the colloids. Optimized conditions include substrates of low and colloids of large electro-kinetic mobility. Then a sorting of colloids by size is observed in binary mixtures with larger particles assembling closer to the ion exchanger beads. Moreover, mono-sized colloids form defect free single domain crystals which grow outside a colloid-free void with facetted inner crystal boundaries centred on the ion exchange particle.