Contactless Rheology of Soft Gels over a Broad Frequency Range

TL;DR

This study introduces a contactless AFM-based method to measure the viscoelastic properties of soft gels across a broad frequency spectrum, revealing elastohydrodynamic coupling and validating a lubrication model.

Contribution

It presents a novel contactless rheology technique using colloidal-probe AFM in liquid, enabling detailed frequency-dependent analysis of soft gel mechanics.

Findings

Elastohydrodynamic coupling observed between flow and gel deformation.

Viscoelastic moduli extracted match the Chasset--Thirion law.

Method effectively probes soft interfaces over wide frequency range.

Abstract

We report contactless measurements of the viscoelastic rheological properties of soft gels. The experiments are performed using a colloidal-probe Atomic Force Microscope (AFM) in a liquid environment and in dynamic mode. The mechanical response is measured as a function of the liquid gap thickness for different oscillation frequencies. Our measurements reveal an elastohydrodynamic (EHD) coupling between the flow induced by the probe oscillation and the viscoelastic deformation of the gels. The data are quantitatively described by a viscoelastic lubrication model. The frequency-dependent storage and loss moduli of the polydimethylsiloxane (PDMS) gels are extracted from fits of the data to the model and are in good agreement with the Chasset--Thirion law. Our results demonstrate that contactless colloidal-probe methods are powerful tools that can be used for probing soft interfaces finely over a wide range of frequencies.