Non‐Equilibrium Assembly of Light‐Activated Colloidal Mixtures

Abstract

The collective phenomena exhibited by artificial active matter systems present novel routes to fabricating out-of-equilibrium microscale assemblies. Here, the crystallization of passive silica colloids into well-controlled 2D assemblies is shown, which is directed by a small number of self-propelled active colloids. The active colloids are titania-silica Janus particles that are propelled when illuminated by UV light. The strength of the attractive interaction and thus the extent of the assembled clusters can be regulated by the light intensity. A remarkably small number of the active colloids is sufficient to induce the assembly of the dynamic crystals. The approach produces rationally designed colloidal clusters and crystals with controllable sizes, shapes, and symmetries. This multicomponent active matter system offers the possibility of obtaining structures and assemblies that cannot be found in equilibrium systems.

Engineering Contactless Particle–Particle Interactions in Active Microswimmers

“…See Supporting Information for the derivation of Equation (4). Similar to our recent study on Janus sphere dimer conformations, the parameter subspace (α, α′) of  E can be reduced by symmetry arguments.…”

“…Active propulsion and the powering of nanomotors, [1][2][3][4][5][6][7][8] microbots, [3,[9][10][11][12][13][14] and nanomachines [15,16] have been the subject of intense research over the past decade. These studies have not only led to better understanding of nonequilibrium active matter, [17] but have also facilitated numerous practical applications [18,19] such as small scale cargo delivery, [20][21][22][23][24] sensing, [25][26][27] and nanoscale actuation within complex fluids.…”

“…[28] Currently, the behavior of individual active particles is well documented and mostly understood. However, as this field advances, greater emphasis is being placed upon investigating and engineering the interactions between swimmers, [4,[29][30][31][32][33] for the next wave of advanced applications. The majority of the available studies on the interactions between active colloids have demonstrated selfassembly via direct contact excluded volume interactions and through powered motility of the mobile entities, [34][35][36][37] e.g., the particles come into contact to form self-assembled clusters that translate and rotate.…”

“…We did not magnetize the particles before dispersal as magnetized Janus spheres were observed to rapidly self-assembled as a result of their permanent dipoles from the ferromagnetic Ni. However, as this field advances, greater emphasis is being placed upon investigating and engineering the interactions between swimmers, [4,[29][30][31][32][33] for the next wave of advanced applications. We note this alignment of the Janus director in the absence of a magnetic field is due to interactions between the particles and the solid boundary.…”

Chemical Nanomotors at the Gram Scale Form a Dense Active Optorheological Medium

“…[43] Since Tempol is also an oxygen scavenger, it suppresses the formation of gaseous bubbles and keeps the reaction mixture stable for long periods of time. [12,45,46] It is seen that without light (UV 365 nm), i.e., in the absence of activity, the particles exhibit Brownian motion (Figure 1b). The holes react with hydroxide ions to produce hydroxyl radicals.…”