We have a new paper to be published in ACS Photonics on “Optothermal evolution of active colloidal matter in defocused laser trap”

In the context of non-equilibrium statistical mechanics, it is relevant to ask : how does a system of (active) Brownian particles respond to environmental cues ?

Structured light in the form of an optical trap can facilitate a platform to create unconventional, environmental cues in which Brownian particles can dynamically assemble and evolve as a function of space and time.

In this work, we utilize a simple defocused laser trap and study the evolutionary dynamics of thermally active colloids (polystyrene spheres infused with iron oxide). We observe a variety of (nonlinear) dynamical states including hovering of a pair, a kind of synchrony among the assembled colloids in the trap (see video).

Thanks to the great efforts of Dipta and Rahul from my group, we have been able to study and unveil the complex forces at play. The dual contribution of optical potential of the laser and thermophoretic interaction of colloids were revealed by systematic experiments and numerical simulations leading to this elaborate report.

This study further motivates interesting questions in the context of microscopic heat engines where the light and heat created in an optical trap can lead to some interesting nonlinear dynamics of soft matter systems. Another prospect is to characterize structured optothermal fields using Brownian motors as microscopic probes in an optical trap. More on this in the coming month….

all videos related to the work on our lab youtube channel

preprint version of the paper on arxiv : https://arxiv.org/abs/2203.08904

I will post the published version of the article when available