A flexible rheometer design to measure the visco-elastic response of soft solids over a wide range of frequency

TL;DR

This paper introduces a versatile rheometer that non-invasively measures the visco-elastic properties of soft solids across a broad frequency spectrum using electromagnetic excitation and interferometric detection.

Contribution

The novel rheometer design employs magnetic surface excitation and optical measurement to accurately assess visco-elastic responses over wide frequencies without direct contact.

Findings

Successfully measured PDMS gel rheology showing scale-free behavior

Achieved high accuracy over a broad frequency range

Validated the method with theoretical and experimental data

Abstract

We present a flexible set-up for determining the rheology of visco-elastic materials which is based on the mechanical response of a magnet deposited at the surface of a slab of material and excited electromagnetically. An interferometric measurement of the magnet displacement allows one to reach an excellent accuracy over a wide range of frequency. Except for the magnet, there is no contact between the material under investigation and the apparatus. At low frequency, inertial effects are negligible so that the mechanical response, obtained through a lock-in amplifier, directly gives the material complex modulus. At high frequency, damped waves are emitted and the rheology must be extracted numerically from a theoretical model. To validate the design, the instrument was used to measure the rheology of a test PDMS gel which presents an almost perfect scale free response at high frequency.