The dark side of microrheology: Non-optical techniques

Microrheology probes the mesoscale between bulk rheology, which provides an integral sample response, and nanorheology, which refers to a local response at a molecular confinement level. The term ‘microrheology’ is often used to refer to optical particle tracking methods that measure a local response of a sample. In contrast to this, non-optical microrheology techniques generally allow two different effects to be studied: actual confinement effects on the rheology and boundary effects such as slip. Investigating the mesoscale range has additional advantages such as the possibility to perform measurements with small sample volumes and at high shear rates. This review bundles the wide array of non-optical techniques into five categories: adaptations to a conventional rotational rheometer, sliding plate rheometry on a micrometer scale, microfluidics, piezo vibrators and radial channel flows. The concept of each set of techniques is described, together with their operational window and examples of recent studies.