Tunable Brownian Vortex at the Interface

TL;DR

This paper demonstrates a tunable Brownian vortex at a liquid-air interface by applying a nonconservative force, revealing how thermal fluctuations and advection create circulatory motion that reflects interface fluctuations.

Contribution

It introduces a method to generate and analyze Brownian vortices at interfaces using external forces and flow, providing new insights into interface fluctuation measurement.

Findings

Brownian vortexes can be controlled at liquid-air interfaces.

The angular velocity of vortex motion correlates with interface fluctuations.

Thermal fluctuations and advection jointly influence vortex dynamics.

Abstract

A general kind of Brownian vortexes are demonstrated by applying an external nonconservative force field to a colloidal particle bound by a conservative optical trapping force at a liquid-air interface. As the liquid medium is translated at a constant velocity with the bead trapped at the interface, the drag force near the surface provide enough rotational component to bias the particle's thermal fluctuations in a circulatory motion. The interplay between the thermal fluctuations and the advection of the bead in constituting the vortex motions is studied, inferring that the angular velocity of the circulatory motion offers a comparative measure of the interface fluctuations.