Direct measurement of the viscocapillary lift force near a liquid interface

TL;DR

This paper reports the first direct measurement of a viscocapillary lift force on a particle near a liquid interface, revealing how the force varies with distance and validating a theoretical model.

Contribution

It provides the first direct experimental quantification of the viscocapillary lift force and confirms the theoretical soft lubrication model predictions.

Findings

Lift force increases as particle approaches the interface.

Force saturates at small distances.

Experimental results agree with the theoretical model.

Abstract

Lift force of viscous origin is widespread across disciplines, from mechanics to biology. Here, we present the first direct measurement of the lift force acting on a particle moving in a viscous fluid along the liquid interface that separates two liquids. The force arises from the coupling between the viscous flow induced by the particle motion and the capillary deformation of the interface. The measurements show that the lift force increases as the distance between the sphere and the interface decreases, reaching saturation at small distances. The experimental results are in good agreement with the model and numerical calculation developed within the framework of the soft lubrication theory.