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Emergence of reconfigurable wires and spinners via dynamic self-assembly.

Kokot G, Piet D, Whitesides GM, Aranson IS, Snezhko A - Sci Rep (2015)

Bottom Line: The energy injection rate, and properties of the environment are important control parameters that influence the outcome of dynamic self-assembly.The spinners emerge via spontaneous breaking of the uniaxial symmetry of the energizing magnetic field.Demonstration of the formation and disaggregation of particle assemblies suggests strategies to form new meso-scale structures with the potential to perform functions such as mixing and sensing.

View Article: PubMed Central - PubMed

Affiliation: Complex Matter Department, Jozef Stefan Institute, Jamova 39, 1000 Ljubliana, Slovenia.

ABSTRACT
Dissipative colloidal materials use energy to generate and maintain structural complexity. The energy injection rate, and properties of the environment are important control parameters that influence the outcome of dynamic self-assembly. Here we demonstrate that dispersions of magnetic microparticles confined at the air-liquid interface, and energized by a uniaxial in-plane alternating magnetic field, self-assemble into a variety of structures that range from pulsating clusters and single-particle-thick wires to dynamic arrays of spinners (self-assembled short chains) rotating in either direction. The spinners emerge via spontaneous breaking of the uniaxial symmetry of the energizing magnetic field. Demonstration of the formation and disaggregation of particle assemblies suggests strategies to form new meso-scale structures with the potential to perform functions such as mixing and sensing.

No MeSH data available.


Dynamic self-assembled structures at the air-liquid interface.(a) Schematics of the experiment. A uni-axial alternating magnetic field is applied parallel to the air-liquid interface. (b) Phase diagram illustrating different states of magnetic dispersion (~102 −103 particles) versus the amplitude and frequency of the applied magnetic field. Region 1 depicts pulsating clusters. Region 2 corresponds to a gas of spinners. Region 3 delineates phase boundaries of the perpendicular cloud phase. Region 4 corresponds to dynamic wires. Particles form dense static clusters in Region 5. Regions marked with diagonal lines pattern indicate a wide hysteretic domain where neighboring structures co-exist. (c) Loose pulsating cluster observed at 20 Hz, 27 Oe magnetic field. Scale bar is 2 mm. (d) Dynamic particle-thick wire formed at 180 Hz, 40 Oe magnetic field. Scale bar is 2 mm. (e) Snapshot of a perpendicular cloud consisting of continuously rearranging short chains. The cloud is extended perpendicular to the axis of the applied magnetic field (40 Hz, 40 Oe) in striking contrast to the cluster phase or dynamic wires. Scale bar is 2 mm. (f) Dynamics of a single spinner within one period of the driving alternating magnetic field (29 Oe, 50 Hz). Length of the spinner is 460 μm. (g) Spinner phase formed at 50 Hz, 29 Oe magnetic field. Short chains of particles rotate in either direction with the frequency of the applied magnetic field. Clock- and anti-clock-wise spinners are illustrated by arrows. Scale bar is 1 mm.
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f1: Dynamic self-assembled structures at the air-liquid interface.(a) Schematics of the experiment. A uni-axial alternating magnetic field is applied parallel to the air-liquid interface. (b) Phase diagram illustrating different states of magnetic dispersion (~102 −103 particles) versus the amplitude and frequency of the applied magnetic field. Region 1 depicts pulsating clusters. Region 2 corresponds to a gas of spinners. Region 3 delineates phase boundaries of the perpendicular cloud phase. Region 4 corresponds to dynamic wires. Particles form dense static clusters in Region 5. Regions marked with diagonal lines pattern indicate a wide hysteretic domain where neighboring structures co-exist. (c) Loose pulsating cluster observed at 20 Hz, 27 Oe magnetic field. Scale bar is 2 mm. (d) Dynamic particle-thick wire formed at 180 Hz, 40 Oe magnetic field. Scale bar is 2 mm. (e) Snapshot of a perpendicular cloud consisting of continuously rearranging short chains. The cloud is extended perpendicular to the axis of the applied magnetic field (40 Hz, 40 Oe) in striking contrast to the cluster phase or dynamic wires. Scale bar is 2 mm. (f) Dynamics of a single spinner within one period of the driving alternating magnetic field (29 Oe, 50 Hz). Length of the spinner is 460 μm. (g) Spinner phase formed at 50 Hz, 29 Oe magnetic field. Short chains of particles rotate in either direction with the frequency of the applied magnetic field. Clock- and anti-clock-wise spinners are illustrated by arrows. Scale bar is 1 mm.

Mentions: Surface tension confines the ferromagnetic microparticles (~90 μm) with intrinsically pinned magnetic moments (see Methods) to the surface of the water-air interface. An alternating magnetic field applied parallel to the interface (Fig. 1a) exerts torque on them. The torque is dissipated locally in the liquid and generates hydrodynamic flows around each particle. Consequently, the particles interact by two temporally related, but physically distinct types of forces: magnetic (dipole-dipole interactions) and hydrodynamic. Dynamic self-assembly reflects the interplay between magnetic interactions and hydrodynamic flows. The relative contributions of these two primary interactions are modulated by the parameters of the energizing alternating magnetic field. As a result, the system exhibits a remarkable diversity of quasi-stable dynamic states. The phase diagram in Fig. 1b delineates these various self-assembled phases as a function of the frequency and amplitude of the applied magnetic field. All the states are dynamic, and exist only while energy is supplied by the a.c. magnetic field. Fig. 1c-g illustrates major distinctive phases.


Emergence of reconfigurable wires and spinners via dynamic self-assembly.

Kokot G, Piet D, Whitesides GM, Aranson IS, Snezhko A - Sci Rep (2015)

Dynamic self-assembled structures at the air-liquid interface.(a) Schematics of the experiment. A uni-axial alternating magnetic field is applied parallel to the air-liquid interface. (b) Phase diagram illustrating different states of magnetic dispersion (~102 −103 particles) versus the amplitude and frequency of the applied magnetic field. Region 1 depicts pulsating clusters. Region 2 corresponds to a gas of spinners. Region 3 delineates phase boundaries of the perpendicular cloud phase. Region 4 corresponds to dynamic wires. Particles form dense static clusters in Region 5. Regions marked with diagonal lines pattern indicate a wide hysteretic domain where neighboring structures co-exist. (c) Loose pulsating cluster observed at 20 Hz, 27 Oe magnetic field. Scale bar is 2 mm. (d) Dynamic particle-thick wire formed at 180 Hz, 40 Oe magnetic field. Scale bar is 2 mm. (e) Snapshot of a perpendicular cloud consisting of continuously rearranging short chains. The cloud is extended perpendicular to the axis of the applied magnetic field (40 Hz, 40 Oe) in striking contrast to the cluster phase or dynamic wires. Scale bar is 2 mm. (f) Dynamics of a single spinner within one period of the driving alternating magnetic field (29 Oe, 50 Hz). Length of the spinner is 460 μm. (g) Spinner phase formed at 50 Hz, 29 Oe magnetic field. Short chains of particles rotate in either direction with the frequency of the applied magnetic field. Clock- and anti-clock-wise spinners are illustrated by arrows. Scale bar is 1 mm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4374141&req=5

f1: Dynamic self-assembled structures at the air-liquid interface.(a) Schematics of the experiment. A uni-axial alternating magnetic field is applied parallel to the air-liquid interface. (b) Phase diagram illustrating different states of magnetic dispersion (~102 −103 particles) versus the amplitude and frequency of the applied magnetic field. Region 1 depicts pulsating clusters. Region 2 corresponds to a gas of spinners. Region 3 delineates phase boundaries of the perpendicular cloud phase. Region 4 corresponds to dynamic wires. Particles form dense static clusters in Region 5. Regions marked with diagonal lines pattern indicate a wide hysteretic domain where neighboring structures co-exist. (c) Loose pulsating cluster observed at 20 Hz, 27 Oe magnetic field. Scale bar is 2 mm. (d) Dynamic particle-thick wire formed at 180 Hz, 40 Oe magnetic field. Scale bar is 2 mm. (e) Snapshot of a perpendicular cloud consisting of continuously rearranging short chains. The cloud is extended perpendicular to the axis of the applied magnetic field (40 Hz, 40 Oe) in striking contrast to the cluster phase or dynamic wires. Scale bar is 2 mm. (f) Dynamics of a single spinner within one period of the driving alternating magnetic field (29 Oe, 50 Hz). Length of the spinner is 460 μm. (g) Spinner phase formed at 50 Hz, 29 Oe magnetic field. Short chains of particles rotate in either direction with the frequency of the applied magnetic field. Clock- and anti-clock-wise spinners are illustrated by arrows. Scale bar is 1 mm.
Mentions: Surface tension confines the ferromagnetic microparticles (~90 μm) with intrinsically pinned magnetic moments (see Methods) to the surface of the water-air interface. An alternating magnetic field applied parallel to the interface (Fig. 1a) exerts torque on them. The torque is dissipated locally in the liquid and generates hydrodynamic flows around each particle. Consequently, the particles interact by two temporally related, but physically distinct types of forces: magnetic (dipole-dipole interactions) and hydrodynamic. Dynamic self-assembly reflects the interplay between magnetic interactions and hydrodynamic flows. The relative contributions of these two primary interactions are modulated by the parameters of the energizing alternating magnetic field. As a result, the system exhibits a remarkable diversity of quasi-stable dynamic states. The phase diagram in Fig. 1b delineates these various self-assembled phases as a function of the frequency and amplitude of the applied magnetic field. All the states are dynamic, and exist only while energy is supplied by the a.c. magnetic field. Fig. 1c-g illustrates major distinctive phases.

Bottom Line: The energy injection rate, and properties of the environment are important control parameters that influence the outcome of dynamic self-assembly.The spinners emerge via spontaneous breaking of the uniaxial symmetry of the energizing magnetic field.Demonstration of the formation and disaggregation of particle assemblies suggests strategies to form new meso-scale structures with the potential to perform functions such as mixing and sensing.

View Article: PubMed Central - PubMed

Affiliation: Complex Matter Department, Jozef Stefan Institute, Jamova 39, 1000 Ljubliana, Slovenia.

ABSTRACT
Dissipative colloidal materials use energy to generate and maintain structural complexity. The energy injection rate, and properties of the environment are important control parameters that influence the outcome of dynamic self-assembly. Here we demonstrate that dispersions of magnetic microparticles confined at the air-liquid interface, and energized by a uniaxial in-plane alternating magnetic field, self-assemble into a variety of structures that range from pulsating clusters and single-particle-thick wires to dynamic arrays of spinners (self-assembled short chains) rotating in either direction. The spinners emerge via spontaneous breaking of the uniaxial symmetry of the energizing magnetic field. Demonstration of the formation and disaggregation of particle assemblies suggests strategies to form new meso-scale structures with the potential to perform functions such as mixing and sensing.

No MeSH data available.