Dynamic Assembly of Active Colloids: Theory and Simulation

Abstract

Because they consume energy to drive their motion, systems of active colloids are intrinsically out of equilibrium. In past decades, a variety of intriguing dynamic patterns have been observed in systems of active colloids, which offer a new platform for studying non‐equilibrium physics, in which computer simulation and analytical theory have played an important role. Recent progress in understanding the dynamic assembly of active colloids by using numerical and analytical tools is reviewed, including progress in understanding the motility induced phase separation in the past decade, followed by discussion on the effect of shape anisotropy and hydrodynamics on the dynamic assembly of active colloids.

Time-dependent properties of interacting active matter: Dynamical behavior of one-dimensional systems of self-propelled particles

“…Certain biological systems such as run-and-tumble bacteria or crawling cells, as well as nonbiological systems such as self-driven colloids or artificial swimmers, commonly referred as active matter, can be described in terms of effective models able to capture their salient features [1][2][3]. Active particles display a very rich phenomenology, such as their accumulation at the boundaries [4][5][6][7] and near rigid obstacles [8][9][10][11][12][13] or a kind of nonequilibrium phase-coexistence, known as motility induced phase separation (MIPS) [14][15][16][17][18] occurring even in the absence of attractive [19][20][21][22][23][24][25][26][27][28] or depletion interactions [29]. Selfpropelled particles are far-from-equilibrium systems, showing several dynamical anomalies which have not a Brownian counterpart [30,31].…”

Onsager's variational principle in active soft matter

“…Examples in biology are abundant and occur at all length scales, ranging from bacteria suspensions 3,[9][10][11][12] to animal cells, 2,4 animal cell aggregates (or tissues), [13][14][15][16][17] bird and fish flocks, 18,19 and pedestrian crowds. 20,21 Artificially made active matter 3 includes layers of vibrated granular rods, 1,22 collections of robots, 23 and suspensions of colloidal or nanoscale particles [24][25][26] that are propelled through catalytic activities at their surfaces.…”

“…One of the most interesting questions in the nonequilibrium dynamics of active matter is how the local driving forces operating at the small scale of individual active unit can produce the observable macroscopic emergent phenomena at the large scale of the whole system. Answering this question will not only shed new light on the fundamental statistical mechanics, 3,6,8,26 but also deepen our understanding of biological processes, [1][2][3][4] and help design new generations of biomimetic active materials that balance structural flexibility and stability. 1,3,5 The study of active matter can be brought into the framework of condensed matter physics based on the consideration that the collective behaviors of active matter emerge from the interactions among the constituent self-propelling units and the dissipation mechanisms operating inside the system.…”

“…2 The physical understanding for the emergent structures and behaviors of active soft matter has been rapidly growing, [1][2][3][4][5][6][7][8][9][10] with particular attention paid to dry active matter, 3,18 active polar fluids, 42 active nematics, 43 active gels, 44 and active membranes. 45 Theoretically there have been two major approaches to the study of active soft matter: particle-based models 3,[6][7][8]26,46 and continuum phenomenological models. 1,2,[4][5][6]14,15,43 In particlebased models, the active units are usually modeled as selfpropelled particles with fixed or variable speed and random orientation moving in an inert background, following the seminal work of Vicsek et al 47 It provides a straightforward approach to the study of active soft matter with an emphasis on the order and fluctuations rather than the forces and mechanics.…”

“…1,2,[4][5][6]14,15,43 In particlebased models, the active units are usually modeled as selfpropelled particles with fixed or variable speed and random orientation moving in an inert background, following the seminal work of Vicsek et al 47 It provides a straightforward approach to the study of active soft matter with an emphasis on the order and fluctuations rather than the forces and mechanics. 3,7,8,26 In continuum phenomenological models, active units are represented by a smooth density field rather than individually resolved particles. A continuum model for active soft matter is usually constructed by modifying the dynamic model of a proper reference soft matter system.…”