Self-propelling colloids in optical potentials

• Applicants: Professor Dr. Ivo Buttinoni; Professor Dr. Hartmut Löwen
• Subject Area: Statistical Physics, Nonlinear Dynamics, Complex Systems, Soft and Fluid Matter, Biological Physics ; Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: since 2023
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 522595197

Synthetic active colloids, i.e. microparticles that self-propel in liquid media, offer exciting opportunities to design metamaterials with self-sustaining properties. Autophoretic patchy microparticles undergo, for instance, cooperative motion analogous to swarms and flocks in living matter. These exciting non-equilibrium dynamics is the result of a delicate interplay between self-propulsion, inter-particle interactions and external conditions. While many recent studies have investigated the collective motion of active colloidal suspensions both in bulk and in complex media, the microscopic origin of the interactions between the self-propelling particles and their compliance with environmental stimuli - such as thermal quenches and noise time-dependent random energy landscapes - are still matters of vibrant debates. In this project, we plan to shed light on these fundamental yet unexplored topics by experimentally looking at the motion of active colloids in laser-tweezing potentials and rationalising our observations using Brownian dynamics simulations. Harmonic optical potentials are, in fact, powerful tools in the field of soft condensed matter, but their application to active colloids is so far limited to very few recent examples. We will build upon our recent characterisation of the properties of active Brownian motion in harmonic laser confinements to (1) measure the interaction forces between pairs of active colloids and pinpoint how they affect the response to (2) thermal quenches and (3) noisy environments. In (2), we will focus on the “colloidal Mpemba effect”, which has similarities with the anomalous cooling of water, already know by Aristotle: hot water freezes faster than warm water. In (3), we will consider optical environments that are noisy in time and look for novel dynamical resonances. The first funding period, which purposely investigates the behaviour of single particles and particle pairs to gain fundamental understanding, will motivate projects where noisy landscapes and inter-particle interactions are exploited to program the collective motion of many-particle suspensions. The ultimate goal is to provide guided routes for the assembly of active colloidal materials.

• DFG Programme: Research Grants