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Active structuring of colloidal armour on liquid drops.

Dommersnes P, Rozynek Z, Mikkelsen A, Castberg R, Kjerstad K, Hersvik K, Otto Fossum J - Nat Commun (2013)

Bottom Line: Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal 'ribbons', electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface.In addition, we demonstrate the size control of 'pupil'-like openings in colloidal shells.We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for 'smart armoured' droplets.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Norwegian University of Science and Technology, Hoegskoleringen 5, N-7491 Trondheim, Norway.

ABSTRACT
Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal 'ribbons', electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of 'pupil'-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for 'smart armoured' droplets.

No MeSH data available.


Actively contracting and expanding pupil armour.This is shown in the series of ten images on the top. The drop is viewed along the E-field direction, as indicated by the crosses. At 200 Vmm−1, the drop (of a radius about 1 mm) is partially covered by a clay ribbon, and at 500 Vmm−1 the drop is nearly fully covered. The timescale of switching is seconds (see also Supplementary Movie 3). This is a reversible process as displayed in the bottom panel, where we plot the area of the pupil opening versus time (following changes of the electric field strength). The cartoons in the inset display a perspective view of the process.
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f6: Actively contracting and expanding pupil armour.This is shown in the series of ten images on the top. The drop is viewed along the E-field direction, as indicated by the crosses. At 200 Vmm−1, the drop (of a radius about 1 mm) is partially covered by a clay ribbon, and at 500 Vmm−1 the drop is nearly fully covered. The timescale of switching is seconds (see also Supplementary Movie 3). This is a reversible process as displayed in the bottom panel, where we plot the area of the pupil opening versus time (following changes of the electric field strength). The cartoons in the inset display a perspective view of the process.

Mentions: The above observations suggest that such colloidal films can be actively controlled by electric fields. As a simple illustration of this, we have performed experiments in which we switch between two different field strengths, one that induces a narrow ribbon formation, and a higher field that actively stretches the ribbon and covers the drop, see Fig. 6. Seen through the electrodes, this has the appearance of an expanding and contracting ‘pupil’. The fact that the film rapidly covers the surface at higher field strength cannot be attributed to clay wetting dynamics at the interface (Marangoni), as turning the field off does not lead to rapid coating. There must therefore be an electrically induced force that actively stretches the film armour. The clay itself will modify the electric field, as clay is more conductive than both oils. Thus, there will be free charge accumulation at the edge of the ribbon, and the electric field acting on these charges could induce electro-stretching of the film. A drop fully covered with dense colloidal armour of conducting colloidal particles can be considered as a Faraday cage screening the internal electric field23, and hence removing the necessary conditions for Taylor–Melcher flow.


Active structuring of colloidal armour on liquid drops.

Dommersnes P, Rozynek Z, Mikkelsen A, Castberg R, Kjerstad K, Hersvik K, Otto Fossum J - Nat Commun (2013)

Actively contracting and expanding pupil armour.This is shown in the series of ten images on the top. The drop is viewed along the E-field direction, as indicated by the crosses. At 200 Vmm−1, the drop (of a radius about 1 mm) is partially covered by a clay ribbon, and at 500 Vmm−1 the drop is nearly fully covered. The timescale of switching is seconds (see also Supplementary Movie 3). This is a reversible process as displayed in the bottom panel, where we plot the area of the pupil opening versus time (following changes of the electric field strength). The cartoons in the inset display a perspective view of the process.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4355650&req=5

f6: Actively contracting and expanding pupil armour.This is shown in the series of ten images on the top. The drop is viewed along the E-field direction, as indicated by the crosses. At 200 Vmm−1, the drop (of a radius about 1 mm) is partially covered by a clay ribbon, and at 500 Vmm−1 the drop is nearly fully covered. The timescale of switching is seconds (see also Supplementary Movie 3). This is a reversible process as displayed in the bottom panel, where we plot the area of the pupil opening versus time (following changes of the electric field strength). The cartoons in the inset display a perspective view of the process.
Mentions: The above observations suggest that such colloidal films can be actively controlled by electric fields. As a simple illustration of this, we have performed experiments in which we switch between two different field strengths, one that induces a narrow ribbon formation, and a higher field that actively stretches the ribbon and covers the drop, see Fig. 6. Seen through the electrodes, this has the appearance of an expanding and contracting ‘pupil’. The fact that the film rapidly covers the surface at higher field strength cannot be attributed to clay wetting dynamics at the interface (Marangoni), as turning the field off does not lead to rapid coating. There must therefore be an electrically induced force that actively stretches the film armour. The clay itself will modify the electric field, as clay is more conductive than both oils. Thus, there will be free charge accumulation at the edge of the ribbon, and the electric field acting on these charges could induce electro-stretching of the film. A drop fully covered with dense colloidal armour of conducting colloidal particles can be considered as a Faraday cage screening the internal electric field23, and hence removing the necessary conditions for Taylor–Melcher flow.

Bottom Line: Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal 'ribbons', electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface.In addition, we demonstrate the size control of 'pupil'-like openings in colloidal shells.We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for 'smart armoured' droplets.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Norwegian University of Science and Technology, Hoegskoleringen 5, N-7491 Trondheim, Norway.

ABSTRACT
Adsorption and assembly of colloidal particles at the surface of liquid droplets are at the base of particle-stabilized emulsions and templating. Here we report that electrohydrodynamic and electro-rheological effects in leaky-dielectric liquid drops can be used to structure and dynamically control colloidal particle assemblies at drop surfaces, including electric-field-assisted convective assembly of jammed colloidal 'ribbons', electro-rheological colloidal chains confined to a two-dimensional surface and spinning colloidal domains on that surface. In addition, we demonstrate the size control of 'pupil'-like openings in colloidal shells. We anticipate that electric field manipulation of colloids in leaky dielectrics can lead to new routes of colloidosome assembly and design for 'smart armoured' droplets.

No MeSH data available.