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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.


Drop deformation as a function of the square of the electric field strength.Pure silicone drops are oblate (drop deformation D<0) and the measurements for weak deformations (−0.04<D<0) quite accurately follow the prediction of Taylor–Melcher perturbation theory. Drops with low clay concentration almost follow the same curve as drops without clay. However, with higher clay concentrations the behaviour is qualitatively different: at low field strengths the drop is oblate, but as the field strength increases the drop deformation reverses from oblate to prolate (D>0). This behaviour coincides with the nonlinear electric response of clay particles, at high field strengths clay form increasingly longer conductive dipolar chains that effectively can short-circuit the silicone drop. The three images at the bottom show how a drop with clay concentration in the medium to high regime (that is, 1–1.5 wt%) deforms reversibly as the electric field strength is increased and decreased. The drop radius is about 1 mm. The E-field direction is horizontal in the plane of the panels, as indicated by the arrows.
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f5: Drop deformation as a function of the square of the electric field strength.Pure silicone drops are oblate (drop deformation D<0) and the measurements for weak deformations (−0.04<D<0) quite accurately follow the prediction of Taylor–Melcher perturbation theory. Drops with low clay concentration almost follow the same curve as drops without clay. However, with higher clay concentrations the behaviour is qualitatively different: at low field strengths the drop is oblate, but as the field strength increases the drop deformation reverses from oblate to prolate (D>0). This behaviour coincides with the nonlinear electric response of clay particles, at high field strengths clay form increasingly longer conductive dipolar chains that effectively can short-circuit the silicone drop. The three images at the bottom show how a drop with clay concentration in the medium to high regime (that is, 1–1.5 wt%) deforms reversibly as the electric field strength is increased and decreased. The drop radius is about 1 mm. The E-field direction is horizontal in the plane of the panels, as indicated by the arrows.

Mentions: At higher clay concentrations, the ribbon width increases when the electric field is increased, as shown in Fig. 5. This is opposite to what can be expected within the Taylor–Melcher model for a particle-free pure oil drop where the EHD flow increases with field strength, which should result in increased compression of the ring and not stretching. We have previously observed that Fh chain formation in silicone oil gives non-ohmic response and strongly enhanced conductivity34, and in the present case, this should diminish the charge buildup on the drop, and thereby suppress the EHD flow. A similar effect is seen in the drop deformation: At high fields and high clay concentrations, the drop deformation can change from oblate to prolate as shown in Fig. 5, indicating that the EHD Taylor flow is suppressed or reversed28.


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)

Drop deformation as a function of the square of the electric field strength.Pure silicone drops are oblate (drop deformation D<0) and the measurements for weak deformations (−0.04<D<0) quite accurately follow the prediction of Taylor–Melcher perturbation theory. Drops with low clay concentration almost follow the same curve as drops without clay. However, with higher clay concentrations the behaviour is qualitatively different: at low field strengths the drop is oblate, but as the field strength increases the drop deformation reverses from oblate to prolate (D>0). This behaviour coincides with the nonlinear electric response of clay particles, at high field strengths clay form increasingly longer conductive dipolar chains that effectively can short-circuit the silicone drop. The three images at the bottom show how a drop with clay concentration in the medium to high regime (that is, 1–1.5 wt%) deforms reversibly as the electric field strength is increased and decreased. The drop radius is about 1 mm. The E-field direction is horizontal in the plane of the panels, as indicated by the arrows.
© Copyright Policy - open-access
Related In: Results  -  Collection

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

f5: Drop deformation as a function of the square of the electric field strength.Pure silicone drops are oblate (drop deformation D<0) and the measurements for weak deformations (−0.04<D<0) quite accurately follow the prediction of Taylor–Melcher perturbation theory. Drops with low clay concentration almost follow the same curve as drops without clay. However, with higher clay concentrations the behaviour is qualitatively different: at low field strengths the drop is oblate, but as the field strength increases the drop deformation reverses from oblate to prolate (D>0). This behaviour coincides with the nonlinear electric response of clay particles, at high field strengths clay form increasingly longer conductive dipolar chains that effectively can short-circuit the silicone drop. The three images at the bottom show how a drop with clay concentration in the medium to high regime (that is, 1–1.5 wt%) deforms reversibly as the electric field strength is increased and decreased. The drop radius is about 1 mm. The E-field direction is horizontal in the plane of the panels, as indicated by the arrows.
Mentions: At higher clay concentrations, the ribbon width increases when the electric field is increased, as shown in Fig. 5. This is opposite to what can be expected within the Taylor–Melcher model for a particle-free pure oil drop where the EHD flow increases with field strength, which should result in increased compression of the ring and not stretching. We have previously observed that Fh chain formation in silicone oil gives non-ohmic response and strongly enhanced conductivity34, and in the present case, this should diminish the charge buildup on the drop, and thereby suppress the EHD flow. A similar effect is seen in the drop deformation: At high fields and high clay concentrations, the drop deformation can change from oblate to prolate as shown in Fig. 5, indicating that the EHD Taylor flow is suppressed or reversed28.

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.