Formation, compression and surface melting of colloidal clusters by active particles.

  title={Formation, compression and surface melting of colloidal clusters by active particles.},
  author={Felix K{\"u}mmel and Parmida Shabestari and Celia Lozano and Giovanni Volpe and Clemens Bechinger},
  journal={Soft matter},
  volume={11 31},
We demonstrate with experiments and numerical simulations that the structure and dynamics of a suspension of passive particles is strongly altered by adding a very small (<1%) number of active particles. With increasing passive particle density, we observe first the formation of dynamic clusters comprised of passive particles being surrounded by active particles, then the merging and compression of these clusters, and eventually the local melting of crystalline regions by enclosed active… 

Figures and Tables from this paper

Metastable Clusters and Channels Formed by Active Particles with Aligning Interactions
We introduce a novel model for active particles with short-range aligning interactions and study their behaviour in crowded environments using numerical simulations. When only active particles are
Nucleation pathway and kinetics of phase-separating active Brownian particles.
Computer simulations are employed to study the nucleation kinetics and the microscopic pathway active Brownian disks take in two dimensions when quenched from the homogeneous suspension to propulsion speeds beyond the binodal, suggesting that the scenario of an effective free energy also extends to the kinetics of phase separation.
Active Atoms and Interstitials in Two-Dimensional Colloidal Crystals.
The motion of a self-phoretic active particle in two-dimensional loosely packed colloidal crystals at fluid interfaces is studied to realize non-close-packed crystalline phases with internal activity.
Clustering-induced velocity-reversals of active colloids mixed with passive particles.
A simple effective model of colloidal mixtures is explored that allows reproducing most aspects seen in experiments, including the morphology and the velocity-reversal of the clusters, particularly the nonreciprocal phoretic attractions of the passive particles to the active colloids' caps.
Propagating interfaces in mixtures of active and passive Brownian particles
The emergent collective dynamics in phase-separated mixtures of isometric active and passive Brownian particles is studied numerically in two-dimensions. A novel steady-state of well-defined
Microscopic field-theoretical approach for mixtures of active and passive particles
We consider a phase field crystal modeling approach for mixtures of interacting active and passive particles in two dimensions. The approach allows us to describe generic properties for such
Emergent behavior in active colloids
Active colloids are microscopic particles, which self-propel through viscous fluids by converting energy extracted from their environment into directed motion. We first explain how articial
Demixing of active particles in the presence of external fields.
It is shown that dynamical demixing may be reduced drastically in the presence of external fields even when the response to the field is the same for both species.
Fabricating large two-dimensional single colloidal crystals by doping with active particles.
It is shown that active dopants both generate and are attracted to defects, such as vacancies and interstitials, which leads to clustering of dopants at grain boundaries, causing rapid coarsening of the crystal domains.
Dimensionality matters in the collective behaviour of active emulsions
Two simple adjustments of the experimental setting lead to a suppression of clustering: either a decrease of the reservoir height below a certain value, or a match of the densities of droplets and surrounding phase, showing that the convection is the key mechanism for the clustering behaviour.


Dynamical clustering and phase separation in suspensions of self-propelled colloidal particles.
A (quasi-)two-dimensional colloidal suspension of self-propelled spherical particles propelled due to diffusiophoresis in a near-critical water-lutidine mixture finds that the driving stabilizes small clusters and undergoes a phase separation into large clusters and a dilute gas phase.
Shear thinning and local melting of colloidal crystals.
It is shown that shear thinning originates from the nonlinear dependence of the locally melted surface area on the drag velocity, providing unprecedented quantitative evidence for the intimate relation between mechanical properties and underlying changes in microscopic structure.
Dynamic clustering in active colloidal suspensions with chemical signaling.
The experimental results are reproduced mathematically by a chemotactic aggregation mechanism, originally introduced to account for bacterial aggregation and accounting here for diffusiophoretic chemical interaction between colloidal swimmers.
Cooperative motion of active Brownian spheres in three-dimensional dense suspensions
The structural and dynamical properties of suspensions of self-propelled Brownian particles of spherical shape are investigated in three spatial dimensions and long-lived cooperative motion of particles in the dense regime is found.
Activity-induced phase separation and self-assembly in mixtures of active and passive particles.
It is found that phase separation from an initially disordered mixture can occur with as little as 15% of the particles being active, and it is shown that a system prepared in a suitable fully segregated initial state reproducibly self-assembles an active "corona," which triggers crystallization of the passive core by initiating a compression wave.
Clustering and heterogeneous dynamics in a kinetic Monte Carlo model of self-propelled hard disks.
  • D. Levis, L. Berthier
  • Physics
    Physical review. E, Statistical, nonlinear, and soft matter physics
  • 2014
It is found that the diffusion constant has a nonmonotonic behavior as self-propulsion is increased at finite density and that activity produces strong deviations from Fickian diffusion that persist over large time scales and length scales, suggesting that systems of active particles generically behave as dynamically heterogeneous systems.
Particle diffusion in a quasi-two-dimensional bacterial bath.
The effect of bacterial motion on micron-scale beads in a freely suspended soap film is studied, and the measured mean-square displacements indicate superdiffusion in short times and normal diffusion in long times.
Athermal phase separation of self-propelled particles with no alignment.
This work shows that the isotropic fluid phase separates well below close packing and exhibits the large number fluctuations and clustering found ubiquitously in active systems.
Crystallizing hard-sphere glasses by doping with active particles.
By performing Brownian dynamics simulations of glassy systems consisting of mixtures of active and passive hard spheres, it is shown that the crystallization of such hard-sphere glasses can be dramatically promoted by doping the system with small amounts of active particles.
Self-motile colloidal particles: from directed propulsion to random walk.
The motion of an artificial microscale swimmer that uses a chemical reaction catalyzed on its own surface to achieve autonomous propulsion is fully characterized experimentally and suggests strategies for designing artificial chemotactic systems.