Nonequilibrium thermodynamics of Janus particle self-assembly

Abstract

We compute the energetic cost of formation of Janus particle structures. Using an approach that couples particle dynamics to the evolution of fuel concentration in the medium, which we consider to be initially inhomogeneous, we show the different types of emerging structures. The energy dissipated in the formation of such structures is obtained from the entropy production rate, which is a non-monotonic function of the fraction of assembled particles and, thus, different in each self-assembly regime. An analysis of the free energy of these particles allows us to establish a thermodynamic criterion of structure formation based on the behavior of chemical potential as a function of the fraction of assembled particles.

Minimal numerical ingredients describe chemical microswimmers’ 3-D motion

“…23,24 It is generally accepted that a more complete description of such "chemically active colloids" requires the full solution of their phoretic fields, including details of the colloids, the substrate, and the solution composition. [25][26][27] Unfortunately, such detailed descriptions call for a high level of technical expertise, are system-specific due to phoretic mobility parameters, have only been solved for spherical and ellipsoidal structures, and do not easily allow the inclusion of thermal fluctuations, which are critical when describing the dynamics of micronscale objects.…”

“…33 Recent experimental studies investigating tracer flows around chemical microswimmers 34 and their directed motion under flow (“rheotaxis”) 35,36 have also indicated that the flow fields generated by such active agents are characteristic of squirmer-type systems. Therefore, “coarse-graining” Janus chemical microswimmers as squirmers provides a viable approach to model their behaviour despite neglecting the (albeit important) contributions arising from chemical fields 26,27 and an asymmetric surface. 33…”

“…33 Recent experimental studies investigating tracer flows around chemical microswimmers 34 and their directed motion under flow ("rheotaxis") 35,36 have also indicated that the flow fields generated by such active agents are characteristic of squirmertype systems. Therefore, "coarse-graining" Janus chemical microswimmers as squirmers provides a viable approach to model their behaviour despite neglecting the (albeit important) contributions arising from chemical fields 26,27 and an asymmetric surface. 33 A number of numerical strategies have been implemented to simulate the coarse-grained dynamics of (chemical) microswimmers, amongst which a multi-particle-collision dynamics (MPCD) description of the solvent is perhaps the most frequently invoked due to its ability to include thermal fluctuations at a lower computational cost than e.g.…”