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The influence of an external flow on the dynamics of active deformable particles demands a detailed understanding of the involved mechanism due to their prominent applications in medical and indust...

We present a simple chemical strategy for the formation of a self-propelling cluster via the process of capture and assembly of passive colloids on the surface of a chemically active colloid. The two species of colloids that are isotropic and Brownian otherwise interact to form propelling cluster. With the help of coarse-grained numerical simulations, we show that a chemically active colloid can induce diffusiophoretic motility to nearby chemically inert colloids towards itself. This propulsion and then self-assembly can then lead to the formation of active cluster. We observe the formation of propelling dimers, trimers, tetramers, etc. depending on the chemical activity and size of the colloids., 11 figures, 2 tables

In the presence of a chemically active particle, a nearby chemically inert particle can respond to a concentration gradient and move by diffusiophoresis. The nature of the motion is studied for two cases: first, a fixed reactive sphere and a moving inert sphere, and second, freely moving reactive and inert spheres. The continuum reaction-diffusion and Stokes equations are solved analytically for these systems and microscopic simulations of the dynamics are carried out. Although the relative velocities of the spheres are very similar in the two systems, the local and global structures of streamlines and the flow velocity fields are found to be quite different. For freely moving spheres, when the two spheres approach each other the flow generated by the inert sphere through diffu- siophoresis drags the reactive sphere towards it. This leads to a self-assembled dimer motor that is able to propel itself in solution. The fluid flow field at the moment of dimer formation changes direction. The ratio of sphere sizes in the dimer influences the characteristics of the flow fields, and this feature suggests that active self-assembly of spherical colloidal particles may be manipulated by sphere-size changes in such reactive systems.

Self-propelling chemical motors have thus far required the fabrication of Janus particles with an asymmetric catalyst distribution. Here, we demonstrate that simple, isotropic colloids can spontaneously assemble to yield dimer motors that self-propel. In a mixture of isotropic titanium dioxide colloids with photo-chemical catalytic activity and passive silica colloids, light illumination causes diffusiophoretic attractions between the active and passive particles and leads to the formation of dimers. The dimers constitute a symmetry-broken motor, whose dynamics can be fully controlled by the illumination conditions. Computer simulations reproduce the dynamics of the colloids and are in good agreement with experiments. The current work presents a simple route to obtain large numbers of self-propelling chemical motors from a dispersion of spherically symmetric colloids through spontaneous symmetry breaking.

We investigate the dynamics of an active deformable particle in external shear flow. The active deformable particle under consideration is a diffusiophoretic vesicle that exhibits motility due to the asymmetric chemical reaction on its surface. The vesicle was constructed using the triangulated surface model, where a combination of chemically active and inactive vertices results in its propulsion. In most practical situations, the dynamics of active particles are affected by their environment and the external flow field is one such example. In this work, we observe the transition of vesicle dynamics from simple directed motion to a circular motion on application of shear flow, leading to a cycloidal trajectory. A detailed study about the dynamics of the active vesicle has been carried out here emphasizing the type of motion, shape, and tank-treading of the vesicle in shear. An elaborate comparison of active and passive vesicles has also been made.