Fluid viscoelasticity triggers fast transitions of a Brownian particle in a double well optical potential

TL;DR

This study observes how viscoelastic fluids significantly increase the transition rates of Brownian particles in a double well potential, contrasting with behavior in Newtonian fluids, and compares results with a theoretical model.

Contribution

First direct experimental observation of Brownian particle transitions in a viscoelastic fluid within a bistable optical potential, validated by a generalized Langevin equation model.

Findings

Transition rates are drastically amplified in viscoelastic fluids.

Fluid relaxation during crossing events influences particle dynamics.

Experimental results align with theoretical predictions.

Abstract

Thermally activated transitions are ubiquitous in nature, occurring in complex environments which are typically conceived as ideal viscous fluids. We report the first direct observations of a Brownian bead transiting between the wells of a bistable optical potential in a viscoelastic fluid with a single long relaxation time. We precisely characterize both the potential and the fluid, thus enabling a neat comparison between our experimental results and a theoretical model based on the generalized Langevin equation. Our findings reveal a drastic amplification of the transition rates compared to those in a Newtonian fluid, stemming from the relaxation of the fluid during the particle crossing events.