Conformations and dynamics of active star polymers

We study conformations and dynamics of active star polymers. The analysis shows that active star polymers stretching behaviour is quite different from that of active linear chains. The visual inspection of conformations and bond-bond correlations reveal a better coordination for the alignment and coordination of bonds for the star polymers than for the linear counterparts. The architecture substantially affects the chain extension transition at high values of active force. The scaling laws for the shape factor and the arm asphericity ratio established for the passive star polymers coincide with the passive case for active force values below the transition. For the values above the transition range the scaling of these quantities switches to different values.Comment: 14 pages, 17 figure

Diffusiophoretically induced interactions between chemically active and inert particles

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

Colloidal chemotaxis and a biased random walk model with finite mean first-passage time

We introduce a power-law distance-dependent biased random walk model with a tuning parameter $(\sigma)$ in which finite mean first-passage times are realizable if σ is less than a critical value $\sigma_c$ . We perform numerical simulations in one dimension to obtain $\sigma_c \approx 1.14$ . A three-dimensional variant of this model is argued to be related to the phenomenon of chemotaxis. Diffusiophoretic theory supplemented with coarse-grained simulations for colloidal chemotaxis establish the connection with the specific value of $\sigma = 2$ as a consequence of in-built solvent diffusion