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SUMMARY:Fluctuations and Structure at Active Interfaces - Margarida Telo d
 a Gama (Universidade de Lisboa)
DTSTART:20240611T135000Z
DTEND:20240611T142000Z
UID:TALK214669@talks.cam.ac.uk
DESCRIPTION:The simplest class of active soft matter may be modelled at th
 e particle level by a system of self-propelled Brownian particles (ABPs) a
 nd at the hydrodynamic level by the (active) model B+ for the dynamics of 
 a conserved scalar order parameter field. Studies revealed surprising coll
 ective behavior\, notably phase separation in systems of purely repulsive 
 particles\, known as motility induced phase separation (MIPS) [1]. Even fo
 r these systems fundamental questions\, such as the surface tension [2] an
 d the scaling of interfacial fluctuations [3] were addressed only recently
 .\nEarly work based on computer simulations of phase separated ABPs in two
  dimensions (2D) reported an interfacial roughness compatible with equilib
 rium Edwards-Wilkinson behaviour [4\,5] in contrast with results from non-
 linear field theory that predict the existence of a MIPS universality clas
 s (qKPZ) away from the critical region [3]. One suggestion is that the sys
 tem of ABPs undergoes bubbly phase separation [6\,3] for which no theoreti
 cal predictions are available.\nHere we consider phase separation of ABPs 
 on a 2D lattice and perform simulations using rejection-free Kinetic Monte
  Carlo (KMC) methods [7] to access long length and time scales\, over a wi
 de range of parameters: at fixed activity system sizes L = 10 to 6500 (in 
 lattice units) and at fixed L activities from near-critical to deep in the
  phase separated system (persistence length lp = 50 to 230). &nbsp\;\nWe f
 ound different regimes: lp/L>1\, where w(t) saturates with L\, and lp/L<1\
 , where w(t) does not saturate with L. The crossover occurs at lp/L = 1. I
 nspection of the interface reveals the emergence of interfacial (quasi) pe
 riodic structures with period ~ lp. The activity driven structure is confi
 rmed by the scaling of the structure factor peak\, with 1/lp. Finally\, a 
 third regime is observed near the critical point (lp=50) where the interfa
 ce is structureless. The behaviour of the auto-correlation function confir
 ms the existence of long-lived interfacial structures that decay at the lo
 west activities. At large activity the decay of the interfacial structures
  was not observed in the time frame of the simulations. The nature of thes
 e structures and their dynamical behaviour suggests that the phase separat
 ion may be bubbly rather than MIPS. Finally\, near the critical point the 
 auto-correlation function exhibits a fat tail.\nClearly\, further work is 
 needed (and is underway) to understand the rich behaviour of active interf
 aces.\nReferences\n\nE. Cates and J. Tailleur\, Motility-Induced Phase Sep
 aration\, Annu. Rev. Condens. Matter Phys.\, 6\, 219 (2015).\nFausti\, E. 
 Tjhung\, M.&thinsp\;E. Cates\, and C. Nardini\, Capillary Interfacial Tens
 ion in Active Phase Separation\, Phys. Rev. Lett.\, 127\, 068001\; Erratum
  Phys. Rev. Lett. 128\, 219901 (2021)\nBesse\, G. Fausti\, M.&thinsp\;E. C
 ates\, B. Delamotte\, and C. Nardini\, Interface Roughening in Nonequilibr
 ium Phase-Separated Systems\, Phys. Rev. Lett.\, 130\, 187102 (2023).\nBia
 lk&eacute\;\, J. T. Siebert\, H. L&ouml\;wen\, and T. Speck\, Negative int
 erfacial tension in phase-separated active Brownian particles\, Phys. Rev.
  Lett.\, 115\, 098301 (2015).\nPatch\, D. M. Sussman\, D. Yllanes\, and M.
  C. Marchetti\, Curvature-dependent tension and tangential flows at the in
 terface of motility-induced phases\, Soft Matter\, 14\, 7435&ndash\;7445 (
 2018).\nTjhung\, C. Nardini\, and M. E. Cates\, Cluster phases and bubbly 
 phase separation in active fluids: Reversal of the ostwald process\, Phys.
  Rev. X 8\, 031080 (2018).\nNeta\, M. Tasinkevych\, M. M. Telo da Gama\, C
 . S. Dias\, Wetting of a solid surface by active matter\, Soft Matter\, 17
 \, 2468-2478 (2021).\nSurfaces and Interfaces of Soft Active Matter\, J. M
 . Cordeiro\, MSc Thesis\, University of Lisbon\, 2023\n
LOCATION:Seminar Room 1\, Newton Institute
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