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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.


Silicone oil drop covered simultaneously with PE beads and metallic-coated glass beads.The applied electric field strength is 250 Vmm−1. The E-field direction is horizontal in the plane of the panels, as indicated by the arrow. The PE beads only form equatorial ribbons, and the metallic-coated particles only form chain-like structures. The dynamic ‘pupil effect’ observed for clay particles (see Fig. 6) cannot be realized for any of these cases in the present experiments. The drop radius is about 1 mm.
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f8: Silicone oil drop covered simultaneously with PE beads and metallic-coated glass beads.The applied electric field strength is 250 Vmm−1. The E-field direction is horizontal in the plane of the panels, as indicated by the arrow. The PE beads only form equatorial ribbons, and the metallic-coated particles only form chain-like structures. The dynamic ‘pupil effect’ observed for clay particles (see Fig. 6) cannot be realized for any of these cases in the present experiments. The drop radius is about 1 mm.

Mentions: We have shown that electric fields can induce structural assembly of colloidal armour on oil drops, including ‘equatorial’ ribbons and ‘longitudinal’ dipolar chains. Electrohydrodynamic circulation flows inside the drop and dipole interaction between particles can account for the observations. The armour width can be actively controlled by the strength of the electric field and we have shown that this effect is intimately linked to the magnitude of polarizability contrast between particles and the drop oil and colloidal particle conductivity (Supplementary Table S1). Thus in the present experiments, the ‘pupil effect’ can only be observed with the clay particles, as our insulating beads only form equatorial ribbons, and metallic-coated particles only form chain-like structures. This is illustrated in Fig. 8, where we observe a drop covered simultaneously with insulating beads and metallic-coated glass beads. It would be interesting to extend this study to mixtures of different particles, which could lead to more advanced electrically controlled self-assembled surface structures. Solidification of these structures can be induced by UV light or heating to produce anisotropic functional colloidosomes11. The method we have demonstrated here is easily transportable to microfluidic devices that include use of electric fields39. Soft matter is characterized by being easily deformable by external fields or forces. The observed electro-stretching of the clay armour on drops is an example of 2D soft matter. To our knowledge, this is the first realization of a Winslow electro-rheological type system3132 confined to a 2D surface. In 3D space, it is well established that electro-rheological chains often attract and form large bundles40. In our case, we did not observe bundling on drop surfaces, rather the chains repel each other, and are regularly spaced in a stable configuration.


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)

Silicone oil drop covered simultaneously with PE beads and metallic-coated glass beads.The applied electric field strength is 250 Vmm−1. The E-field direction is horizontal in the plane of the panels, as indicated by the arrow. The PE beads only form equatorial ribbons, and the metallic-coated particles only form chain-like structures. The dynamic ‘pupil effect’ observed for clay particles (see Fig. 6) cannot be realized for any of these cases in the present experiments. The drop radius is about 1 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f8: Silicone oil drop covered simultaneously with PE beads and metallic-coated glass beads.The applied electric field strength is 250 Vmm−1. The E-field direction is horizontal in the plane of the panels, as indicated by the arrow. The PE beads only form equatorial ribbons, and the metallic-coated particles only form chain-like structures. The dynamic ‘pupil effect’ observed for clay particles (see Fig. 6) cannot be realized for any of these cases in the present experiments. The drop radius is about 1 mm.
Mentions: We have shown that electric fields can induce structural assembly of colloidal armour on oil drops, including ‘equatorial’ ribbons and ‘longitudinal’ dipolar chains. Electrohydrodynamic circulation flows inside the drop and dipole interaction between particles can account for the observations. The armour width can be actively controlled by the strength of the electric field and we have shown that this effect is intimately linked to the magnitude of polarizability contrast between particles and the drop oil and colloidal particle conductivity (Supplementary Table S1). Thus in the present experiments, the ‘pupil effect’ can only be observed with the clay particles, as our insulating beads only form equatorial ribbons, and metallic-coated particles only form chain-like structures. This is illustrated in Fig. 8, where we observe a drop covered simultaneously with insulating beads and metallic-coated glass beads. It would be interesting to extend this study to mixtures of different particles, which could lead to more advanced electrically controlled self-assembled surface structures. Solidification of these structures can be induced by UV light or heating to produce anisotropic functional colloidosomes11. The method we have demonstrated here is easily transportable to microfluidic devices that include use of electric fields39. Soft matter is characterized by being easily deformable by external fields or forces. The observed electro-stretching of the clay armour on drops is an example of 2D soft matter. To our knowledge, this is the first realization of a Winslow electro-rheological type system3132 confined to a 2D surface. In 3D space, it is well established that electro-rheological chains often attract and form large bundles40. In our case, we did not observe bundling on drop surfaces, rather the chains repel each other, and are regularly spaced in a stable configuration.

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.