Ramin Golestanian FRS

Abstract:

This thesis investigates the conformation and dynamics of active polymers driven tangentially along their backbone in complex environments, including porous structures, granular media, and aqueous settings. Active polymers, in contrast to passive systems, are self-driven entities capable of converting energy into mechanical motion, a characteristic observed in both biological and synthetic systems. Through advanced computer simulations, this research examines the interplay between polymer flexibility, self-propulsion strength, and environmental features such as fluid-mediated interactions and obstacle arrangements in porous media. The findings reveal how conformational transitions, such as coil-stretch and spiral formations, influence polymers' transport. By elucidating the influence of activity on both conformational and dynamical properties, this thesis enhances the understanding of transport phenomena in active matter. The results have broad implications for biological processes, such as intracellular transport and active motion of polymer-like worms, and for the development of synthetic active materials

Abstract:

Breaking spatial symmetry is an essential requirement for phoretic active particles to swim at low Reynolds number. This fundamental prerequisite for swimming at the micro scale is fulfilled either by chemical patterning of the surface of active particles or alternatively by exploiting geometrical asymmetries to induce chemical gradients and achieve self-propulsion. In the present paper, a far-field analytical model is employed to quantify the leading-order contribution to the induced phoretic velocity of a chemically homogeneous isotropic active colloid near a finite-sized disk of circular shape resting on an interface separating two immiscible viscous incompressible Newtonian fluids. To this aim, the solution of the phoretic problem is formulated as a mixed-boundary-value problem that is subsequently transformed into a system of dual integral equations on the inner and outer domains. Depending on the ratio of different involved viscosities and solute solubilities, the sign of phoretic mobility and chemical activity, as well as the ratio of particle–interface distance to the radius of the disk, the isotropic active particle is found to be repelled from the interface, be attracted to it, or reach a stable hovering state and remain immobile near the interface. Our results may prove useful in controlling and guiding the motion of self-propelled phoretic active particles near aqueous interfaces.