Observation of Brownian elastohydrodynamic forces acting on confined soft colloids

TL;DR

This paper introduces a novel microscopy-based method to analyze the complex coupling of fluid flow, surface forces, and fluctuations affecting soft colloids in confined environments, revealing a significant transient Brownian force.

Contribution

It presents a new approach combining holographic microscopy and statistical inference to precisely measure forces and mobilities at the nanoscale in complex, confined systems.

Findings

Detection of a large, transient soft Brownian force

High-precision reconstruction of local mobilities and forces

Implications for microbiological transport and chemical reactions

Abstract

Confined motions in complex environments are ubiquitous in microbiology. These situations invariably involve the intricate coupling between fluid flow, soft boundaries, surface forces and fluctuations. In the present study, such a coupling is investigated using a novel method combining holographic microscopy and advanced statistical inference. Specifically, the Brownian motion of softmicrometric oil droplets near rigid walls is quantitatively analyzed. All the key statistical observables are reconstructed with high precision, allowing for nanoscale resolution of local mobilities and femtonewton inference of conservative or non-conservative forces. Strikingly, the analysis reveals the existence of a novel, transient, but large, soft Brownian force. The latter might be of crucial importance for microbiological and nanophysical transport, target finding or chemical reactions in crowded environments, and hence the whole life machinery.