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Autonomous colloidal crystallization in a galvanic microreactor
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Image of FIG. 1.
FIG. 1.

Guided colloidal aggregation using galvanic microreactor arrays. (a)Schematic of the microreactor (not to scale). See text for details. (b-c)In situ images of PS particles aggregating preferentially at the edges (b) or near the centers (c) of triangular copper electrodes (enhanced online). In (c) the onset of double layer formation can be seen as dark structures covering parts of the colloidal crystals. After termination of the experiment and rinsing, however, only the first layer of colloidal particles remains cemented to the electrode. (d) 2D colloidal crystals on triangular electrodes after termination of the experiment and rinsing with DI water. Inset: larger area view. Around each particle-covered electrode, a dark halo can be seen which we attribute to the deposition of reaction products on the gold cathode (see below). Scalebars: 50 μm. [URL: http://dx.doi.org/10.1063/1.4755807.1] [URL: http://dx.doi.org/10.1063/1.4755807.2]doi: 10.1063/1.4755807.1.

doi: 10.1063/1.4755807.2.

Image of FIG. 2.
FIG. 2.

Particle cementation and crystallinity of aggregates. (a) PS particles aggregated on top of a reaction product layer. Scale bar 2 μm. (b-c) SEM images of a 20 μm triangle from an array of triangles with (b) 80 μm and (c)40 μm separation used in an aggregation experiment after sonication. Scale bar 10 μm. Insets: Optical dark-field images before sonication. (d) Section of the result presented in Fig. 1(d) (40 μm triangles with a separation of 60 μm), (e) colloidal particles aggregated on 40 μm triangles with a separation of 80 μm (experiment conducted at reduced particle volume fraction of 0.06%). Values of the calculated order parameter ψ 6 are displayed next to the respective triangular electrodes. (f) Schematic showing different stages of the particle aggregation process (see text).

Image of FIG. 3.
FIG. 3.

(a) Separation of PS (dark) and silica (bright) particles during dissolution of a copper line electrode on gold. The x-axis indicates positions relative to right edge of copper electrode. (b) Velocity of silica particles: negative velocities correspond to a motion towards the copper anode while positive velocities indicate motion away from the copper. The x-axis corresponds to the axis shown in (a). (c) Spatially resolved dissolution rate of a 50 μm wide copper anode (for 950 μm electrode spacing).

Image of FIG. 4.
FIG. 4.

(a) Schematic of bulk electrolyte flow. (b) Cross sections of dissolution rate at different electrode spacing s. (c) Velocity of silica particles located on the gold cathode (y = 0 μm) for different electrode spacing s.



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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Autonomous colloidal crystallization in a galvanic microreactor