Active polymers

Active polymers are composed of units which can produce fluid flow around it. Depending on the nature of the activity and the domain, the polymers produce a series of spontaneous motion. For instance, extensile semiflexible polymers produce autonomous motion driven by the active flows and contractile polymers shows rotational motion when confined in a spherical cavity. Our study fouces on the collective dynamics of active polymers in confined geometry and demonstrates the dynamic formation of knots and links, nonequilibrium transition between isotropic and liquid crystalline states and athermal creation and annihilation of different kind of defects. Moreover, the non-equilibrium fluid flows produced by atcive polymers can be harnessed with smart designs to transport vesicles ballistically.

Entanglement in volume confinement

The topological constraint that polymers cannot slide through each other due to its connectivity, allows all polymer fluids to contain entanglements to some degree depending on the system properties such as volume fraction. The effect of these entanglements is explored and studied in detail by the reptation model first proposed by de-Gennes. However, such theories are limited to passive systems. Here, we extend these studies to the case of active polymers in spherical confinement. We find that at moderate polymer densities, spontaneous and persistent collective motion of extensile polymers leads to chain entanglement which cannot be released through active reptation. On the contrary, contractile polymers always form entangled state independent of density.
Manna et al, Soft Matter 15, 477 (2019)

Dynamics of disclinations in surface confinement

We study suspension of extensile and contractile active polymers confined to the surface of a spherical volume. Spontaneous and persistent collective motion of extensile polymers in surface confinement leads to the generation of half-integer topological defects, which remarkably, are neither created or annihilated in pairs. Instead, defects appear and disappear through active reptation of individual polymer. Our results reproduce the phenomenology of several recent experiments and suggest non-equilibrium kinetic routes to polymeric structures that are otherwise difficult to obtain in equilibrium.
Manna et al, Soft Matter 15, 477 (2019)

Flexibility enhances the diffusivity of short active colloidal chains

We demonstrate that flexibility enhances the diffusivity of a short active colloidal chain. The active colloidal chain is modeled as a chain of active beads which produce extensile hydrodynamic flow. We found that the diffusivity of active colloidal chain increases with the increase of flexibility. In contrast, there are no significant changes in the diffusivity of passive chain with the flexibility. Our results of diffusivity of the active colloidal chain are in perfect agreement with the experimental results obtained using chains of catalytic micro-particles. Our results suggest that the enhancement of diffusivity in these systems can be attributed to the interplay between chain conformation fluctuations and active hydrodynamic flow.
Biswas et al, ACS Nano 11, 10 (2017)

Colloidal transport by an active filaments

Enhanced colloidal transport beyond the limit imposed by diffusion is usually achieved through external fields. We demonstrate the ballistic transport of a colloidal sphere using internal sources of energy provided by an attached active filament. The speed and efficiency of transport depend on the dynamical conformational states of the filament.This transport mechanism has a remarkable resemblance to the flagellar propulsion of microorganisms which suggests its utility in biomimetic systems.
Manna et al, J. Chem. Phys. 146 , 024901 (2017)