Turbulent mixing by microscopic self-assembled spinners

1. A system for mixing particles, comprising:

a liquid comprising inert particles and defining a liquid and air interface;

magnetic microparticles suspended at the liquid and air interface; and

a magnetic source configured to apply a uniaxial alternating magnetic field parallel to the liquid and air interface, wherein the uniaxial alternating magnetic field promotes the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid, which in turn promotes a diffusive motion of the inert particles;

wherein the system has a non-monotonic dependence of an active diffusion coefficient on a size of the inert particles.

2. The system of claim 1 , wherein the magnetic microparticles are self-assembled spinners within a range of an excitation parameter of the magnetic source.

3. The system of claim 2 , wherein the excitation parameter comprises a frequency in a range of 50-80 Hz.

4. The system of claim 3 , wherein the excitation parameter comprises an amplitude.

5. The system of claim 1 , wherein the magnetic microparticles inject energy at a rate that is tunable in response to a frequency and an amplitude of the magnetic field.

6. The system of claim 5 , wherein the magnetic microparticles form self-assembled microscopic chains that rotate in arbitrary directions in response to the magnetic field.

7. The system of claim 6 , wherein the self-assembled microscopic chains of the magnetic microparticles generate vigorous vortical flows at the liquid and air interface, and the vortical flows are in response to a torque that is influenced by the rate of the injected energy.

8. The system of claim 7 , wherein the self-assembled microscopic chains of the magnetic microparticles exhibit chaotic dynamics due to self-generated advection flows.

9. The system of claim 1 , wherein the turbulent motion also promotes a diffusive motion of the magnetic microparticles.

10. The system of claim 9 , wherein the diffusive motion is active diffusion that has the active diffusion coefficient that is a non-monotonic function of the active particle number density for the inert particles.

11. The system of claim 1 wherein the active diffusion coefficient for the inert particles is greater than or equal to 1.0 mm 2 s −1 and an active diffusion coefficient for the magnetic microparticles is less than 1.0 mm 2 s −1 .

12. The system of claim 11 , wherein each active diffusion coefficient is over a frequency in a range from 50-80 Hz.

13. A method of mixing particles, comprising:

providing a liquid comprising inert particles and defining a liquid and air interface;

suspending magnetic microparticles at the liquid and air interface; and

promoting the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid by applying a uniaxial alternating magnetic field parallel to the liquid and air interface using a magnetic source, wherein the turbulent motion promotes a diffusive motion of at least one of the magnetic microparticles and the inert particles;

wherein the method has a non-monotonic dependence of an active diffusion coefficient on a size of the inert particles.

14. The method of claim 13 , further comprising adjusting a strength the turbulent motion of the magnetic microparticles using at least one of a frequency and an amplitude of the magnetic field.

15. The method of claim 14 , wherein a range of the frequency is 50-80 Hz.

16. The method of claim 13 , wherein the magnetic microparticles form self-assembled spinners that rotate in arbitrary directions in response to the application of the magnetic field, and wherein the self-assembled microscopic chains of the magnetic microparticles generate vigorous vortical flows at the liquid and air interface.

17. The method of claim 16 , wherein the active diffusion coefficient for the inert particles is larger than an active diffusion coefficient of the magnetic microparticles.

18. The method of claim 17 , wherein the active diffusion coefficient for the inert particles exhibits a monotonic increase with a number density until a density to sustain a spinner phase reaches a threshold.

19. The method of claim 13 , wherein the active diffusion coefficient for the inert particles is greater than or equal to 1.0 mm 2 s −1 and an active diffusion coefficient for the magnetic microparticles is less than 1.0 mm 2 s −1 , and wherein each active diffusion coefficient is over a frequency in a range from 50-80 Hz.

20. A system for mixing particles, comprising:

a liquid comprising inert particles and defining a liquid and air interface;

magnetic microparticles suspended at the liquid and air interface; and

a magnetic source configured to apply a uniaxial alternating magnetic field parallel to the liquid and air interface, wherein the uniaxial alternating magnetic field promotes the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid, which in turn promotes a diffusive motion of the inert particles;

wherein the turbulent motion also promotes a diffusive motion of the magnetic microparticles;

wherein the diffusive motion is active diffusion that has an active diffusion coefficient that is a non-monotonic function of the active particle number density for the inert particles.

21. A system for mixing particles, comprising:

a liquid comprising inert particles and defining a liquid and air interface;

magnetic microparticles suspended at the liquid and air interface; and

a magnetic source configured to apply a uniaxial alternating magnetic field parallel to the liquid and air interface, wherein the uniaxial alternating magnetic field promotes the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid, which in turn promotes a diffusive motion of the inert particles,

wherein an active diffusion coefficient for the inert particles is greater than or equal to 1.0 mm 2 s −1 and an active diffusion coefficient for the magnetic microparticles is less than 1.0 mm 2 s −1 .

22. A method of mixing particles, comprising:

providing a liquid comprising inert particles and defining a liquid and air interface;

suspending magnetic microparticles at the liquid and air interface; and

promoting the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid by applying a uniaxial alternating magnetic field parallel to the liquid and air interface using a magnetic source, wherein the turbulent motion promotes a diffusive motion of at least one of the magnetic microparticles and the inert particles;

wherein the magnetic microparticles form self-assembled spinners that rotate in arbitrary directions in response to the application of the magnetic field, and wherein the self-assembled microscopic chains of the magnetic microparticles generate vigorous vortical flows at the liquid and air interface;

wherein an active diffusion coefficient for the inert particles is larger than an active diffusion coefficient of the magnetic microparticles.

23. A method of mixing particles, comprising:

providing a liquid comprising inert particles and defining a liquid and air interface;

suspending magnetic microparticles at the liquid and air interface; and

promoting the formation of microscopic spinning chains of magnetic microparticles resulting in a turbulent motion of the liquid by applying a uniaxial alternating magnetic field parallel to the liquid and air interface using a magnetic source, wherein the turbulent motion promotes a diffusive motion of at least one of the magnetic microparticles and the inert particles;

wherein an active diffusion coefficient for the inert particles is greater than or equal to 1.0 mm 2 s −1 and an active diffusion coefficient for the magnetic microparticles is less than 1.0 mm 2 s −1 , and wherein each active diffusion coefficient is over a frequency in a range from 50-80 Hz.