Arrested states in persistent active matter: Gelation without attraction

Abstract

We explore phase separation and kinetic arrest in active hard-core particles, in the limit of infinite persistence time of their active orientation. The passive limit of the model we consider, namely crossshaped particles on a square lattice, exhibits a first order transition from a fluid phase to a solid phase with increasing density. Quenches into the two-phase coexistence region exhibit a crossover from a simple fluid to an extremely slowly coarsening regime in which concentrated immobile clusters with local crystalline order emerge. These states represent an aging passive glass in this system. Adding persistent, yet small, active bias to the particle dynamics enhances and speeds up the aggregation of such clusters of immobile particles, creating states that resemble the passive glass at lower densities. For large active bias, the dense, immobile clusters proliferate until a spanning network bridges the system leading to percolation of an arrested phase, reminiscent of gelation in attracting colloids. Active particles remaining within the voids inside this network collect to form an interface which "wets" the surface of the arrested solid. We use an asymmetric simple exclusion process to map out a non-equilibrium phase diagram for this system. The phase diagram exhibits intriguing similarities to that of attracting colloids, however, we observe novel phases such as solid-liquid-void states that have no analogue in systems with zero activity.

Dynamic heterogeneity in active glass-forming liquids is qualitatively different compared to its equilibrium behaviour

“…Motivated by the experimental findings, such systems have been studied via simulations [19][20][21][22][23][24] as well as extended analytical theories of equilibrium glasses, such as mode-coupling theory (MCT) [25][26][27][28][29][30] and random first order transition theory [29]. Studies on single-particle dynamics [31] and jamming transition [19,32,33] have also been extended for active systems. The current consensus in the field is that activity pushes the glass and jamming transitions to lower temperature or higher density, though the nature of an active glass seems to be qualitatively similar to an equilibrium glass and the difference lies in the quantitative description, such as in the form of long-ranged velocity correlation [30,34] or the evolving effective temperature, T ef f , much like a sheared system [25,26].…”

Displacement correlations in disordered athermal networks

“…Such situations naturally arise in dense systems with activity where jammed regions arise with the directions and magnitudes of the individual active forces being randomly distributed. [45][46][47]. We assume the relaxation timescale to achieve the mechanical equilibrium is considerably less than the timescale of the angular fluctuations of the pinned forces.…”

Enhanced Phonon Peak in Four-point Dynamic Susceptibility in the Supercooled Active Glass-forming Liquids

“…On the other hand, glassy liquids or supercooled liquids are the systems whose particles start to move collectively with decreasing temperature (increasing density) until they get kinetically trapped near their putative glass transition temperature (density) [3][4][5][6][7][8]. The former is a non-equilibrium system that shows spectacular dynamical properties like largescale ordering, flocks, swarms, etc., and is one of the current hot topics of research [9][10][11][12][13][14][15][16][17][18][19][20]. Many biological systems are shown to have dynamical properties similar to the glass-forming liquids in the presence of active driving.…”