High-density MIPS dynamics and evolution remain unresolved

Determine the microscopic dynamics, structural organization, and temporal evolution of the coexisting dense and dilute phases that arise during motility-induced phase separation in active Brownian particles at high packing fractions, in order to clarify critical aspects of the high-density regime.

Background

Active Brownian particles (ABPs) undergo motility-induced phase separation (MIPS), producing coexisting dense and dilute phases without attractive forces. While many features of MIPS have been studied, the high-density regime presents unresolved complexities related to how particles interact and reorganize over time within and across phases.

This paper analyzes ABP contact networks during MIPS to reveal structural features in dense and dilute phases, but explicitly notes that key microscopic and temporal aspects of high-density MIPS remain not yet understood. Addressing this problem would bridge micro-level dynamics with emergent network structures and phase behavior.

References

Despite significant advances in theoretical, computational, and experimental investigations, critical aspects of MIPS, at high densities, such as microscopic dynamics, structural complexities, and the temporal evolution of these phase-separated states, remain not yet understood.

— Contact temporal network during motility induced phase separation (2506.08642 - Salas et al., 10 Jun 2025) in Introduction (Section 1)