Propelling chemical dimer motors can spontaneously self-assemble from isotropic non-propelling colloids.

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 diffusiophoresis 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.

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.

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