Few-body hydrodynamic interactions probed by optical trap pulling experiment

TL;DR

This study experimentally investigates hydrodynamic interactions between micro-beads in optical traps, providing insights into viscous coupling effects at micron scales and millisecond timescales relevant for colloidal assembly and optical tweezer resolution.

Contribution

It offers direct experimental validation of hydrodynamic coupling at larger scales and timescales, enhancing understanding of colloidal interactions and optical trapping techniques.

Findings

Hydrodynamic coupling observed at micron scales.

Measured relaxation times of entrained beads.

Validated theoretical models with experimental data.

Abstract

We study the hydrodynamic coupling of neighboring micro-beads placed in a dual optical trap setup allowing us to precisely control the degree of coupling and directly measure time-dependent trajectories of the entrained beads. Average experimental trajectories of a probe bead entrained by the motion of a neighboring scan bead are compared with theoretical computation, illustrating the role of viscous coupling and setting timescales for probe bead relaxation. The findings provide direct experimental corroborations of hydrodynamic coupling at larger, micron spatial scales and millisecond timescales, of relevance to hydrodynamic-assisted colloidal assembly as well as improving the resolution of optical tweezers. We repeat the experiments for three bead setups.