Yield stress “in a flash”: investigation of nonlinearity and yielding in soft materials with an optofluidic microrheometer

Abstract

Yield stress materials deform as elastic solids or flow as viscous liquids, depending on the applied stress, which also allows them to trap particles below a certain size or density...

Deformation profiles and microscopic dynamics of complex fluids during oscillatory shear experiments

“…Despite being a technique that has had enormous success, passive microrheology is unable to provide complete rheological information in all cases of interest. For instance, if the storage modulus of the material is too large or if one is interested in the non-linear rheological properties, it is often preferred to recur to active microrheology, in which at least one of the embedded particles is driven by an external force obtained, for instance, via optical or magnetic trapping 1,[3][4][5] . Passive and active microrheology techniques are very powerful tools for the characterization of soft materials, as they can access high frequencies and enable a space-resolved study of the rheological properties of complex, heterogeneous systems 3 .…”

Roadmap for optical tweezers

“…The integrated microrheometer has been initially validated by characterizing well-known fluids, such as water-glycerol mixtures, providing very reliable results. The potential of the system has then been confirmed by accurately measuring the regimes of the mechanical response of non-Newtonian fluids, such as DNA hydrogels and yield stress materials [202,203].…”

“…Force intensity up to 1 nN, with good trapping stability, has been demonstrated, also making possible the reliable investigation of the viscoelastic properties of a vast class of materials in a nonlinear viscosity regime. As an example [203] reports the results obtained on an aqueous suspension of packed, swollen microgels, a well-studied example of simple yield stress fluids.…”