arXiv subjects

Edward B. Steager

Publications and source records attributed to Edward B. Steager.

3 recordsLinked to original sources

arXiv2026

A sweeping twist defect as a topological flagellum that drives colloid motion

Nematic liquid crystals can dramatically reconfigure under dynamic forcing, providing exciting opportunities in active matter. Here, we study a hybrid disk colloid rotated by an external field which generates a dynamic companion topological defect. The disk moves faster when the defect sweeps across the disk's face. We identify the defect as a non-singular twist wall, characterize the twist energy landscape, and identify the sweeping motion as a topological instability. As the defect sweeps, it reverses the handedness of twist and lowers the free energy in the fluid in the gap above the disk. Landau-de Gennes modeling shows that the sweeping wall behaves as a propagating director texture: the director field is nearly stationary in the wall frame, while nematogens rotate locally as the wall passes. The nematogens' rotation generates a viscous stress on the surface of the disk that hastens its propulsion. Thus, the defect acts as a flagellum that powers colloid swimming, providing an example of a dissipative topological structure whose dynamics can be harnessed to perform useful work.

cond-mat.soft↗

arXiv2022

Nematic colloidal micro-robots as physically intelligent systems

Physically intelligent micro-robotic systems exploit information embedded in micro-robots, their colloidal cargo, and their milieu to interact, assemble and form functional structures. Nonlinear anisotropic fluids like nematic liquid crystals (NLCs) provide untapped opportunities to embed interactions via their topological defects, complex elastic responses, and their ability to dramatically restructure in dynamic settings. Here we design and fabricate a 4-armed ferromagnetic micro-robot to embed and dynamically reconfigure information in the nematic director field, generating a suite of physical interactions for cargo manipulation. The micro-robot shape and surface chemistry are designed to generate a nemato-elastic energy landscape in the domain that defines multiple modes of emergent, bottom-up interactions with passive colloids. Micro-robot rotation expands the ability to sculpt interactions; the energy landscape around a rotating micro-robot is dynamically reconfigured by complex far-from-equilibrium dynamics of the micro-robot's companion topological defect. These defect dynamics allow transient information to be programmed into the domain and exploited for top-down cargo manipulation. We demonstrate robust micro-robotic manipulation strategies that exploit these diverse modes of nemato-elastic interaction to achieve cargo docking, transport, release, and assembly of complex reconfigurable structures at multi-stable sites. Such structures are of great interest to future developments of LC-based advanced optical device and micro-manufacturing in anisotropic environments.

cond-mat.soft↗

arXiv2021

Topological defect-propelled swimming of nematic colloids

Non-equilibrium dynamics of topological defects can be used as a fundamental propulsion mechanism in microscopic active matter. Here, we demonstrate swimming of topological defect-propelled colloidal particles in (passive) nematic fluids through experiments and numerical simulations. Dynamic swim strokes of the topological defects are driven by colloidal rotation in an external magnetic field, causing periodic defect rearrangement which propels the particles. The swimming velocity is determined by the colloid's angular velocity, sense of rotation and defect polarity. By controlling them we can locomote the particles along different trajectories. We demonstrate scattering -- that is, the effective pair interactions -- of two of our defect-propelled swimmers, which we show is highly anisotropic and depends on the microscopic structure of the defect stroke, including the local defect topology and polarity. More generally, this work aims to develop biomimetic active matter based on the underlying relevance of topology.

cond-mat.soft↗