Discriminating stochastic processes for the assessment of materials properties by diffusion measurements

Title data

Metzler, Ralf ; Weiss, Matthias:
Discriminating stochastic processes for the assessment of materials properties by diffusion measurements.
In: Physical Chemistry Chemical Physics. Vol. 27 (June 2025) . - pp. 14350-14358.
ISSN 1463-9084
DOI: https://doi.org/10.1039/D5CP01378J

Official URL:

Abstract in another language

Assessing the materials properties of complex media, e.g. colloidal suspensions or intracellular fluids, frequently relies on quantifying the diffusive motion of tracer particles. In particular, from the particles’ mean squared displacement (MSD) one may infer the complex shear modulus of the medium. Yet, experimentally the same power-law forms of the MSDs emerge for tracer diffusion in very different environments. For example, diffusive motion in a static maze of fractal obstacles (obstructed diffusion, OD) and motion in viscoelastic fluids (often described by fractional Brownian motion, FBM) can show an identical sublinear MSD scaling, but an MSD-derived complex shear modulus is meaningless for OD as the system does not feature any viscoelasticity. Here we show that OD and FBM trajectories are highly similar in many observables, including the MSD and the autocovariance function that reports on the memory of the particle motion. The Gaussianity and/or the asphericity of trajectories, extracted with single-particle tracking, allows for a proper discrimination of OD and FBM, facilitating a meaningful interpretation of the materials properties of the medium. In contrast, techniques that only monitor particle number fluctuations in a region of interest are not capable of discriminating highly similar random processes like FBM and OD as they only rely on the MSD. We therefore highly recommend the use of the more informative tracking of single particles when aiming to asses materials properties of the medium under investigation.

Further data

Item Type:	Article in a journal
Refereed:	Yes
Institutions of the University:	Faculties > Faculty of Mathematics, Physics und Computer Science > Department of Physics > Chair Experimental Physics I - Physics of Living Matter > Chair Experimental Physics I - Physics of Living Matter - Univ.-Prof. Dr. Matthias Weiss
Result of work at the UBT:	Yes
DDC Subjects:	500 Science > 530 Physics 500 Science > 570 Life sciences, biology
Date Deposited:	10 Jul 2025 12:29
Last Modified:	10 Jul 2025 12:29
URI:	https://eref.uni-bayreuth.de/id/eprint/94169