(a) Schematic drawing of the electric bottle. The thick glass slides (light gray) and the very thin electrodes (dark gray) are not drawn to scale. The respective directions of gravity and the (ac) electric field when the cell was mounted on the stage of the microscope are indicated with arrows. (b) Schematic side view of the cell, with an artistic impression of the contour lines of the electric field. The dotted line indicates the position, halfway the height of the sample space, for which the profile in panel (c) was drawn up. (c) Electric field profile calculated at an applied voltage . The dashed lines indicate the position of the slit edges (see text for all the relevant parameters).
Bragg reflection images showing the crystallization induced by dielectrophoretic compression at [refer to Fig. 1(c) for the corresponding electric field strength at the different positions in the sample cell]. The bright reflections set the crystals apart from the more diffusively scattering colloidal fluid. The symbols in the images at and indicate the positions of the confocal images shown in Figs. 3 and 5. All photographs were taken in transmission using white-light illumination.
Confocal microscopy images before and after of compression at . The numbers correspond to different positions along the particle-density profile, as indicated in Fig. 2. The arrows indicate the three equivalent close-packed directions of the hexagonal lattice.
The change in the particle volume fraction during dielectrophoretic compression at three different positions in the sample cell. Curve I was the center of the slit (position 0), curve II was just inside the slit , and curve III was just outside the slit . The lines connecting the data points are meant as a guide to the eye. The vertical dashed lines indicate the course of the experiment, after turning on at . (1) Field raised to ; (2) field increased further to . The volume fraction of the first crystals (at the arrow) is also indicated (horizontal dotted line). All error bars are based on three repeat measurements.
Confocal microscopy images showing the simultaneous growth and motion of the crystalline bands (at ). (a) Inner edge (slit center at the top side), and (b) outer edge (electrodes at the bottom side), as was indicated in Fig. 2. The dashed lines highlight the circumference of a bleached patch, which served as a landmark.
Comparison of the experimental and calculated particle-density profiles after of compression at . Black dots: Experimental volume fractions mapped onto a hard-sphere suspension (see text); gray line: Calculated density profile for hard spheres. The scaled initial volume fraction is indicated with a solid black line and the position of the slit edges with vertical dashed lines. The experimental data were obtained from particle tracking; the estimated error is .
Bragg reflection image showing the crystal that was formed by of compression at in an electric bottle with a square geometry of the electrode-free area.
(a) Confocal micrograph of one of the outer edges of the melting crystal after at zero field. The slit edge ran parallel to the top side of the image. (b) The change in the particle volume fraction at three different positions in the sample cell after switching off the electric field . Curve I is the center of the slit (position 0), Curve II is just inside the slit , and Curve III is just outside the slit . The lines connecting the data points are a guide to the eye. The original volume fraction of the first crystals is also indicated. All error bars are based on three repeat measurements.
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