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A neutral atom consists of a positively charged nucleus surrounded by a negatively charged electron cloud. When placed in an external electric field, the external electric force pulls the electrons and nucleus apart, opposite to the intrinsic attraction between the nucleus and the electrons. The opposing forces balance each other with a slight shift between the center of masses of the nucleus and the electron cloud, resulting in a polarized atom. On the other hand, a few molecules, like water,...
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Negative differential mobility and trapping in active matter systems.

C Reichhardt1, C J O Reichhardt1

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Active matter particles exhibit complex flow behaviors in random obstacle arrays. Their mobility nonmonotonically changes with activity, showing enhanced flow at low levels and reduced flow at high levels due to particle trapping.

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Area of Science:

  • Physics, Soft Matter
  • Statistical Mechanics
  • Computational Physics

Background:

  • Active matter systems, such as self-propelled particles, exhibit unique emergent behaviors distinct from equilibrium systems.
  • Understanding particle dynamics in disordered media is crucial for applications ranging from microfluidics to biological transport.

Purpose of the Study:

  • To investigate the average velocity and mobility of active matter particles in a random obstacle array as a function of applied drift force.
  • To characterize different flow regimes, including linear response, negative differential mobility, and fully clogged states.
  • To analyze the influence of particle activity and system parameters on transport properties.

Main Methods:

  • Numerical simulations were employed to model the motion of active matter particles.
  • The system consisted of particles interacting with a random array of obstacles under an applied drift force.
  • Key parameters varied included drift force, particle activity, disk density, obstacle density, active run length, and motor force.

Main Results:

  • A linear flow regime was observed at low drift forces, with mobility increasing with drive.
  • At higher drift forces, negative differential mobility emerged due to particles becoming trapped behind obstacles.
  • A fully clogged regime was identified at very high drift forces, where all particles were permanently trapped.
  • Particle mobility showed a nonmonotonic dependence on activity, with enhancement at low activity and reduction at high activity.

Conclusions:

  • The study reveals complex transport phenomena in active matter systems interacting with disorder.
  • Negative differential mobility and clogging are significant emergent behaviors driven by particle-obstacle interactions.
  • System parameters like activity and density critically influence the observed transport regimes, offering insights into the design and behavior of active matter devices.