Unsteady flows uncover the limits of the stress-optic law.

ABSTRACT: Birefringence induced in complex fluid flows, containing anisotropic microstructures, exhibits vibrant patterns, captivating people perceptually. More practically, it has garnered multidisciplinary expectations on the noninvasive characterization of stress fields in flowing materials based on the stress-optic law established for solid materials, prospecting its in situ and in vitro applications. Here, we question such a paradigm by demonstrating the failure of the law in unsteady flows through laboratory experiments. The latter originates from the relaxation of the microscopic structures, characterized by the Deborah number De, which is a dimensionless number that compares the material's relaxation time and the characteristic time of the applied deformation process. Flow birefringence turn

SUBMITTER: Noto D 

PROVIDER: S-EPMC12552630 | biostudies-literature | 2025 Oct

REPOSITORIES: biostudies-literature