Emergent Cometlike Swarming of Optically Driven Thermally Active Colloids

Abstract

We propose a simple system of optically driven colloids that convert light into heat and move in response to self-generated and collectively generated thermal gradients. We show that the system exhibits self-organization into a moving cometlike swarm and characterize the structure and response of the swarm to a light-intensity-dependent external tuning parameter. We observe many interesting features in this nonequilibrium system including circulation and evaporation, intensity-dependent shape, density and temperature fluctuations, and ejection of hot colloids from the swarm tip.

Unusual swelling of a polymer in a bacterial bath

“…The collisions of the bacteria with the chain lead to nonequilibrium (non-thermal) fluctuations of the chain which may result in new phenomena of chain stretching and compaction different from equilibrium solvents. Active matter itself has been intensely explored over the last years, both for living systems as bacteria [4], spermatozoa [5] and mammals [6,7] or is system of artificial microswimmers [8][9][10][11][12][13] with various propulsion mechanisms [14][15][16][17] and a plethora of nonequilibrium pattern formation phenomena were discovered [18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33]. At fixed system boundaries active system show distinct clustering and trapping behaviour [34][35][36][37][38][39][40][41][42][43][44][45] and can be expoited to * kaiser@thphy.uni-duesseldorf.de steer the motion of microrotors and microcarriers [46][47]…”

Shape control and compartmentalization in active colloidal cells

“…Active matter covers a range of length scales that include molecular motors in the cytoskeleton (3)(4)(5), swimming bacteria (6)(7)(8), driven colloids (9,10), flocks of birds and fish (11)(12)(13)(14), and people and vehicles in motion (15). Over the last decade, studies of active matter have demonstrated behavior not seen in equilibrium systems, including giant number fluctuations (16,17), emergent attraction and superdiffusion (18)(19)(20), clustering (21,22), swarming (23)(24)(25)(26)(27), and self-assembled motifs (28,29). These systems provide interesting theoretical and engineering challenges as well as opportunities to explore and target novel behaviors that proceed outside of thermodynamic equilibrium.…”

“…−p + τ nn = κH, [27] where τ nn = n · τ · n is the normal component of the viscous stress at the boundary, and κ is the surface tension of the boundary (in units of ηMr 3=2 =K 1=2 ). Provided that forces due to surface tension are large compared with those due to boundary activity (i.e., κ Rτ′), deformations in the shape of the boundary will be small.…”

Hydrodynamic front-like swarming of phoretically active dimeric colloids

“…Chemically active Janus colloidal particles have already shown clustering and selfassembled structures [12] as well as schooling behavior; and the formation of living crystals has already been observed for light powered micromotors [13,14]. Brownian simulations of thermophilic active colloids predicted the appearance of clustering and comet-like swarming structures [15,16]. Nevertheless, the mechanisms involved in the formation of these structures, the importance of the phoretic and hydrodynamic effects, and the behavior of various types of phoretic swimmers are still very relevant and largely unexplored questions.…”

“…Similar to previous works [10,32], heating is modeled by rescaling the temperature of fluid particles in a short layer (0.08s H ) around the hot beads to a value of T h = 1.5, while keeping the overall average fluid temperature at T = 1.0 using simple velocity rescaling. This constant heating neglects shadowing effects [16], it corresponds to colloids made of materials with the same light refraction index as the solvent, and which in the case of thermophobic behavior will have smaller influence. Simulations are performed using a modified variant of the software package lammps [33], in particular a modified version of the 'srd'-package [34].…”