Controlled assembly of single colloidal crystals using electro-osmotic micro-pumps

Niu, Ran; Oğuz, Erdal C.; Müller, H.; Reinmüller, Alexander; Botin, Denis; Löwen, Hartmut; Palberg, Thomas

doi:10.1039/c6cp07231c

Cited by 35 publications

(45 citation statements)

References 60 publications

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“…The sorting by size is inversed as compared to that observed under low flow conditions. 35 Here, the assembly distance appears to be limited by the dashed line denoting the solvent flow as traced by near buoyant PS2 and also found in simulations of solvent flow at a stationary IEX45 29 Rotation about an axis perpendicular to the propulsion direction and parallel to the substrate can also be seen for Janus-type cargo particles.…”

Section: Discussionsupporting

confidence: 65%

Assembly and Speed in Ion-Exchange-Based Modular Phoretic Microswimmers

et al. 2017

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We report an experimental study on ion-exchange-based modular microswimmers in low-salt water. Cationic ion-exchange particles and passive cargo particles assemble into self-propelling complexes, showing self-propulsion at speeds of several micrometers per second over extended distances and times. We quantify the assembly and speed of the complexes for different combinations of ion-exchange particles and cargo particles, substrate types, salt types and concentrations, and cell geometries. Irrespective of the experimental boundary conditions, we observe a regular development of the assembly shape with increasing number of cargo. Moreover, the swimming speed increases stepwise upon increasing the number of cargo and then saturates at a maximum speed, indicating the active role of cargo in modular swimming. We propose a geometric model of self-assembly to describe the experimental observations in a qualitative way. Our study also provides some constraints for future theoretical modeling and simulation.

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Section: Discussionsupporting

confidence: 65%

Assembly and Speed in Ion-Exchange-Based Modular Phoretic Microswimmers

et al. 2017

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“…35 To obtain high quality crystals, we further coated the negatively charged substrate with positively charged surfactants, which decreases the surface charge and thus the flow strength. 36 The competition between the counterbalancing electrophoretic and electroosmotic flows leads to the sorting of colloidal particles according to their size. Furthermore, it was proved that a finite assembly distance between the colloidal crystal and the IEX is crucial for the formation of high quality crystals.…”

Section: Introductionmentioning

confidence: 99%

Seedless assembly of colloidal crystals by inverted micro-fluidic pumping

Niu

Palberg

2018

Soft Matter

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We propose a simple seedless approach to assemble millimeter sized monolayer single colloidal crystals with desired orientations at predetermined locations on an unstructured charged substrate. This approach utilizes the millimeter-ranged fluid flow on the bottom glass substrate induced by an ion exchange resin (IEX) fixed on top of the closed sample cell. The fluid flow increases with decreasing height of the sample cell and increasing radius R of the IEX. For a single inverted pump, millimeter sized monolayer single crystals of hexagonal close packing can be obtained. For two closely spaced (D ∼ 4R) pumps, the formed crystals have a predefined orientation along the line connecting the two IEX. By patterning IEX into different structures, colloidal crystals of different complex patterns form. The present method paves a convenient way for fabricating high quality monolayer colloidal crystals for a variety of applications.

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“…It spontaneously starts moving when both components bind, typically leaving a pronounced exclusion zone in between. While observed in various experiments [35], only the attraction between resin and colloids has been explained [39][40][41]. However, both the formation of an exclusion zone and the very fact that the modules can self-propel remains elusive, even qualitatively.…”

Section: Introductionmentioning

confidence: 99%

Unraveling modular microswimmers: From self-assembly to ion-exchange-driven motors

et al. 2018

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Active systems contain self-propelled particles and can spontaneously self-organize into patterns making them attractive candidates for the self-assembly of smart soft materials. One key limitation of our present understanding of these materials hinges on the complexity of the microscopic mechanisms driving its components forward. Here, by combining experiments, analytical theory and simulations we explore such a mechanism for a class of active system, modular microswimmers, which self-assemble from colloids and ion-exchange resins on charged substrates. Our results unveil the self-assembly processes and the working mechanism of the ion-exchange driven motors underlying modular microswimmers, which have so far been illusive, even qualitatively. We apply these motors to show that modular microswimmers can circumvent corners in complex environments and move uphill. Our work closes a central knowledge gap in modular microswimmers and provides a facile route to extract mechanical energy from ion-exchange processes. arXiv:1807.10175v2 [cond-mat.soft]

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Controlled assembly of single colloidal crystals using electro-osmotic micro-pumps

Cited by 35 publications

References 60 publications

Assembly and Speed in Ion-Exchange-Based Modular Phoretic Microswimmers

Assembly and Speed in Ion-Exchange-Based Modular Phoretic Microswimmers

Seedless assembly of colloidal crystals by inverted micro-fluidic pumping

Unraveling modular microswimmers: From self-assembly to ion-exchange-driven motors

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