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Issue 19, 2018
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A symmetrical method to obtain shear moduli from microrheology

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Abstract

Passive microrheology typically deduces shear elastic loss and storage moduli from displacement time series or mean-squared displacements (MSD) of thermally fluctuating probe particles in equilibrium materials. Common data analysis methods use either Kramers–Kronig (KK) transformation or functional fitting to calculate frequency-dependent loss and storage moduli. We propose a new analysis method for passive microrheology that avoids the limitations of both of these approaches. In this method, we determine both real and imaginary components of the complex, frequency-dependent response function χ(ω) = χ′(ω) + iχ′′(ω) as direct integral transforms of the MSD of thermal particle motion. This procedure significantly improves the high-frequency fidelity of χ(ω) relative to the use of KK transformation, which has been shown to lead to artifacts in χ′(ω). We test our method on both model and experimental data. Experiments were performed on solutions of worm-like micelles and dilute collagen solutions. While the present method agrees well with established KK-based methods at low frequencies, we demonstrate significant improvement at high frequencies using our symmetric analysis method, up to almost the fundamental Nyquist limit.

Graphical abstract: A symmetrical method to obtain shear moduli from microrheology

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Article information


Submitted
20 Dec 2017
Accepted
21 Mar 2018
First published
21 Mar 2018

This article is Open Access

Soft Matter, 2018,14, 3716-3723
Article type
Paper

A symmetrical method to obtain shear moduli from microrheology

K. Nishi, M. L. Kilfoil, C. F. Schmidt and F. C. MacKintosh, Soft Matter, 2018, 14, 3716
DOI: 10.1039/C7SM02499A

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