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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.


Simulations of dynamic phases.(a) Phase diagram of the dynamic states versus the magnitude and frequency of the alternating magnetic field as obtained from the simulations. Stars depict dynamic wires. Circles correspond to a gas of spinners. Diamonds delineate the perpendicular cloud phase. Triangles correspond to the simulation results where a mixture of different dynamic structures has been observed. Field amplitude H0 is rescaled by μ/(4πa3), where μ is a magnetic moment per particle. Frequency is scaled by 1 Hz. Right axis shows recalculated values of the field amplitude for the particles used in the experiments. (b) Starting configuration of the magnetic suspension in the simulations: particles with initially random orientations are distributed on a perturbed square lattice. Each particle is shown as a sphere with a darker hemisphere corresponding to a magnetic “north pole”. (c) Spinners phase as obtained from simulations. Top sequence of images illustrates rotation of two neighboring spinners over a half-period of the applied magnetic field. Arrows depict the axis of the applied magnetic field. See Supplementary Video 7. (d) Snapshot of a perpendicular cloud phase as obtained from the simulations. The cloud is extended perpendicular to the axis of the applied magnetic field in an agreement with the experimental observations (see Fig. 1e). (e), (f) Formation of dynamic wires. Self-assembly proceeds through a formation and subsequent merging and reorientation of short chain segments. Snapshots of a system after 1700 (e) and 41700 (f) periods of the applied field from the moment the field was turned on. See Supplementary Video 8.
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f4: Simulations of dynamic phases.(a) Phase diagram of the dynamic states versus the magnitude and frequency of the alternating magnetic field as obtained from the simulations. Stars depict dynamic wires. Circles correspond to a gas of spinners. Diamonds delineate the perpendicular cloud phase. Triangles correspond to the simulation results where a mixture of different dynamic structures has been observed. Field amplitude H0 is rescaled by μ/(4πa3), where μ is a magnetic moment per particle. Frequency is scaled by 1 Hz. Right axis shows recalculated values of the field amplitude for the particles used in the experiments. (b) Starting configuration of the magnetic suspension in the simulations: particles with initially random orientations are distributed on a perturbed square lattice. Each particle is shown as a sphere with a darker hemisphere corresponding to a magnetic “north pole”. (c) Spinners phase as obtained from simulations. Top sequence of images illustrates rotation of two neighboring spinners over a half-period of the applied magnetic field. Arrows depict the axis of the applied magnetic field. See Supplementary Video 7. (d) Snapshot of a perpendicular cloud phase as obtained from the simulations. The cloud is extended perpendicular to the axis of the applied magnetic field in an agreement with the experimental observations (see Fig. 1e). (e), (f) Formation of dynamic wires. Self-assembly proceeds through a formation and subsequent merging and reorientation of short chain segments. Snapshots of a system after 1700 (e) and 41700 (f) periods of the applied field from the moment the field was turned on. See Supplementary Video 8.

Mentions: We numerically solved the equations of motion for N particles on a plane. Particles are energized by an in-plane uni-axial magnetic field, and interact due to their magnetic dipole moments, self-induced hydrodynamic flows, and steric repulsion. In simulations, the length was scaled on the particle size, time was scaled by 1/f, where f is the frequency of the applied magnetic field, and field amplitude was scaled by μ/(4πa3), where μ is a magnetic moment per particle. The parameters in the equations of motion were calculated from actual properties of the particles and fluid (size, magnetic susceptibility, viscosity). See Methods for the details of the model and simulations. The simulations successfully reproduced the morphology of experimental phase diagram (Fig. 4a) and captured most of the observed phases (see Fig. 4).


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

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

Simulations of dynamic phases.(a) Phase diagram of the dynamic states versus the magnitude and frequency of the alternating magnetic field as obtained from the simulations. Stars depict dynamic wires. Circles correspond to a gas of spinners. Diamonds delineate the perpendicular cloud phase. Triangles correspond to the simulation results where a mixture of different dynamic structures has been observed. Field amplitude H0 is rescaled by μ/(4πa3), where μ is a magnetic moment per particle. Frequency is scaled by 1 Hz. Right axis shows recalculated values of the field amplitude for the particles used in the experiments. (b) Starting configuration of the magnetic suspension in the simulations: particles with initially random orientations are distributed on a perturbed square lattice. Each particle is shown as a sphere with a darker hemisphere corresponding to a magnetic “north pole”. (c) Spinners phase as obtained from simulations. Top sequence of images illustrates rotation of two neighboring spinners over a half-period of the applied magnetic field. Arrows depict the axis of the applied magnetic field. See Supplementary Video 7. (d) Snapshot of a perpendicular cloud phase as obtained from the simulations. The cloud is extended perpendicular to the axis of the applied magnetic field in an agreement with the experimental observations (see Fig. 1e). (e), (f) Formation of dynamic wires. Self-assembly proceeds through a formation and subsequent merging and reorientation of short chain segments. Snapshots of a system after 1700 (e) and 41700 (f) periods of the applied field from the moment the field was turned on. See Supplementary Video 8.
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC4374141&req=5

f4: Simulations of dynamic phases.(a) Phase diagram of the dynamic states versus the magnitude and frequency of the alternating magnetic field as obtained from the simulations. Stars depict dynamic wires. Circles correspond to a gas of spinners. Diamonds delineate the perpendicular cloud phase. Triangles correspond to the simulation results where a mixture of different dynamic structures has been observed. Field amplitude H0 is rescaled by μ/(4πa3), where μ is a magnetic moment per particle. Frequency is scaled by 1 Hz. Right axis shows recalculated values of the field amplitude for the particles used in the experiments. (b) Starting configuration of the magnetic suspension in the simulations: particles with initially random orientations are distributed on a perturbed square lattice. Each particle is shown as a sphere with a darker hemisphere corresponding to a magnetic “north pole”. (c) Spinners phase as obtained from simulations. Top sequence of images illustrates rotation of two neighboring spinners over a half-period of the applied magnetic field. Arrows depict the axis of the applied magnetic field. See Supplementary Video 7. (d) Snapshot of a perpendicular cloud phase as obtained from the simulations. The cloud is extended perpendicular to the axis of the applied magnetic field in an agreement with the experimental observations (see Fig. 1e). (e), (f) Formation of dynamic wires. Self-assembly proceeds through a formation and subsequent merging and reorientation of short chain segments. Snapshots of a system after 1700 (e) and 41700 (f) periods of the applied field from the moment the field was turned on. See Supplementary Video 8.
Mentions: We numerically solved the equations of motion for N particles on a plane. Particles are energized by an in-plane uni-axial magnetic field, and interact due to their magnetic dipole moments, self-induced hydrodynamic flows, and steric repulsion. In simulations, the length was scaled on the particle size, time was scaled by 1/f, where f is the frequency of the applied magnetic field, and field amplitude was scaled by μ/(4πa3), where μ is a magnetic moment per particle. The parameters in the equations of motion were calculated from actual properties of the particles and fluid (size, magnetic susceptibility, viscosity). See Methods for the details of the model and simulations. The simulations successfully reproduced the morphology of experimental phase diagram (Fig. 4a) and captured most of the observed phases (see Fig. 4).

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.