Active Hydrodynamics Couples Polymer Organization, Shape Fluctuations, and Motility in Deformable Droplets

Abstract

We study semiflexible active polymers confined within a soft, deformable droplet suspended in a fluid using dissipative particle dynamics (DPD) simulations. Extensile and contractile force dipoles along the polymer backbone generate distinct hydrodynamic flow fields that mediate effective interactions between polymer segments. Extensile activity promotes parallel alignment and lateral attraction, whereas contractile activity favors predominantly perpendicular organization, leading to qualitatively different collective behavior. The activity-generated flows couple strongly to the deformable interface, selectively enhancing low-order spherical-harmonic modes associated with long-wavelength droplet deformations. Activity also drives the interfacial relaxation away from passive capillary behavior, with extensile and contractile droplets exhibiting distinct mode-dependent dynamics. These differences in internal organization and interfacial fluctuations strongly influence droplet motility. Extensile activity produces increasingly persistent droplet motion with increasing polymer number, whereas contractile activity can sustain long-lived near-ballistic motion whose duration depends sensitively on polymer number and activity strength. Our results demonstrate how active hydrodynamics governs the interplay between internal structure, interfacial fluctuations, and emergent motility in confined active matter systems.