Theory and Simulations of Active Brownian Systems

• Applicant: Professor Abhinav Sharma, Ph.D.
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Biophysics
• Term: from 2020 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 440884972

• Final Report Year: 2024

Final Report Abstract

Movement is a vital aspect of life, enabling organisms to navigate toward more favorable environments and find food. Various biological systems, from molecular motors within cells to flocks of birds, belong to the category of active matter. In these systems, individual components convert energy into directed motion, propelling themselves forward. This principle applies not only to biological examples but also to synthetic active matter, which consists of self-propelled particles created in laboratories. These particles, typically colloidal in size, move by self-phoresis and operate in low Reynolds number environments, where the particle size is under a few micrometers. The models used to describe their motion extend Brownian motion, taking nonequilibrium dynamics into account. The project aims to investigate how the behavior of synthetic active particles, especially their preferential accumulation, can be controlled using simple design principles. In many cases, the propulsion speed of these particles is not uniform across space, causing them to swim faster in some areas than in others. A key focus is understanding how a single active particle, or multiple particles connected by a potential, respond to such spatial variations in activity. It is generally observed that an active particle, lacking any steering mechanism, tends to linger in regions where it moves more slowly. However, the likelihood of it moving toward more active regions is higher than the probability of it drifting into less active areas. Furthermore, when active particles are connected to passive ”cargo” particles, arranged in polymer-like chains, or attached to other active particles, their collective behavior depends on several factors. These include the friction of the cargo particle, the number of monomers in the polymer, and the orientation of the active particles. Depending on these variables, the particles may accumulate in either high or low activity regions. Additionally, when the activity varies both spatially and temporally, a steady drift of active particles can occur. This allows for the positioning of particles based on their size, even in the absence of a direct coupling between the propulsion direction and the activity gradient.

Publications

• Lorentz forces induce inhomogeneity and flux in active systems. Physical Review Research, 2(1).
  Vuijk, H. D.; Sommer, J. U.; Merlitz, H.; Brader, J. M. & Sharma, A.
  
• Pseudo-chemotaxis of active Brownian particles competing for food. PLOS ONE, 15(4), e0230873.
  Merlitz, Holger; Vuijk, Hidde D.; Wittmann, René; Sharma, Abhinav & Sommer, Jens-Uwe
  
• Chemotaxis of Cargo-Carrying Self-Propelled Particles. Physical Review Letters, 126(20).
  Vuijk, Hidde D.; Merlitz, Holger; Lang, Michael; Sharma, Abhinav & Sommer, Jens-Uwe
  
• Stochastic resetting of active Brownian particles with Lorentz force. Soft Matter, 17(5), 1307-1316.
  Abdoli, Iman & Sharma, Abhinav
  
• Active chiral molecules in activity gradients. The Journal of Chemical Physics, 157(13).
  Muzzeddu, Pietro Luigi; Vuijk, Hidde Derk; Löwen, Hartmut; Sommer, Jens-Uwe & Sharma, Abhinav
  
• Active colloidal molecules in activity gradients. Physical Review E, 106(1).
  Vuijk, Hidde D.; Klempahn, Sophie; Merlitz, Holger; Sommer, Jens-Uwe & Sharma, Abhinav
  
• Collisions Enhance Self-Diffusion in Odd-Diffusive Systems. Physical Review Letters, 129(9).
  Kalz, Erik; Vuijk, Hidde Derk; Abdoli, Iman; Sommer, Jens-Uwe; Löwen, Hartmut & Sharma, Abhinav
  
• Strongly enhanced dynamics of a charged Rouse dimer by an external magnetic field. PNAS Nexus, 1(3).
  Shinde, Rushikesh; Sommer, Jens Uwe; Löwen, Hartmut & Sharma, Abhinav
  
• Tunable Brownian magneto heat pump. Scientific Reports, 12(1).
  Abdoli, Iman; Wittmann, René; Brader, Joseph Michael; Sommer, Jens-Uwe; Löwen, Hartmut & Sharma, Abhinav
  
• Tailoring the escape rate of a Brownian particle by combining a vortex flow with a magnetic field. The Journal of Chemical Physics, 158(10).
  Abdoli, I.; Löwen, H.; Sommer, J.-U. & Sharma, A.
  
• Oscillatory Force Autocorrelations in Equilibrium Odd-Diffusive Systems. Physical Review Letters, 132(5).
  Kalz, Erik; Vuijk, Hidde Derk; Sommer, Jens-Uwe; Metzler, Ralf & Sharma, Abhinav