Research

Synthetic active matter – Superwalking droplets

Superwalking droplets—self-propelled liquid drops bouncing on a vertically vibrated fluid bath—are a novel class of synthetic active matter, where each droplet acts as an energy-consuming particle powered by its interaction with a self-generated wave field. Unlike many synthetic active systems with constant motility, superwalking droplets exhibit rich internal-state dynamics, including transitions between stationary, steady, and oscillatory motion, driven by memory effects in the wave–particle coupling. Such active wave-particle entities have also been shown to exhibit hydrodynamic quantum analogs.

Active matter with internal-state dynamics

Murmurations of birds, schooling of fish, insect swarms, bacterial suspensions, human crowd and swarming of robots/drones are all examples of complex and dynamical collective behaviours that result from complex interactions among individuals. We have explored a collection of particles, coined attractor-driven matter, where we model each particle’s internal complexity by attributing to it an internal state space that is represented by a point on an attracting set of a chaotic dynamical system. We illustrate the rich dynamical and emergent behaviors that can arise from such particles. The formalism provides a flexible means to generate complex dynamical and collective behaviors that may be broadly applied in various contexts.

Nonlinear dynamics of passive and active particles in channel flows

We explore the complex dynamics of particles in fluid flows through confined geometries, focusing on how both active and passive particles behave under the influence of flow profiles and channel shapes relevant to microfluidic applications. Active particles swimming in Poiseuille flow through rectangular channels exhibit a variety of nonlinear trajectories such as periodic swinging, trapping, and chaotic tumbling, that shaped by the interplay between their intrinsic propulsion and the flow velocity. Meanwhile, passive particles suspended in fluid flow through curved microchannels experience focusing effects driven by the balance of inertial lift and secondary flows, leading to bifurcations and tipping phenomena that govern their stable equilibrium positions. These nonlinear behaviors under combined hydrodynamic and geometric effects reveal mechanisms for controlling particle motion and enabling passive separation strategies in microfluidic devices.

Seminar talk: R. Valani and B. Harding (2023, July 5), Inertial Particle Focusing in Curved Ducts: Bifurcation and Dynamics

Active wave-particle entities: Inertial active particles with memory

We explore how the intrinsic coupling between an active particle and its self-generated wave-memory fields gives rise to rich dynamical complexity captured by Lorenz-like nonlinear models.