Abstract
Gelling colloidal suspensions represent an important class of soft materials. Their mechanical response is characterized by a solid-to-liquid transition at a given shear stress level. Moreover, they often exhibit a complex time-dependent rheological behavior known as thixotropy. The viscosity changes find their origin in the microstructure, which depends on flow history. Yet, the structural response of colloidal gels to flow differs fundamentally from most complex fluids, where flow induces orientation. Upon yielding, low to intermediate volume fraction gels break down in a spatially anisotropic way. Bonds in the velocity-velocity gradient plane are broken, whereas microstructural features in other planes are less affected. The subsequent flow-induced microstructural anisotropy is characterized by typical butterfly scattering patterns. However, as yet there was no evidence for the pertinence of this anisotropy for the rheological properties of these systems. In the present work, orthogonal superposition rheometry was first used to evaluate how the flow-induced microstructure affects the viscoelastic properties. It was shown to retain significant elasticity in the velocity-vorticity plane, even when the structure liquefied. Further, the shear-induced mechanical anisotropy was measured using two-dimensional small amplitude oscillatory shear, exploiting the fact that for suitable thixotropic samples the recovery after arresting the flow is relatively slow. It was hence possible to measure the anisotropy of the moduli upon cessation of flow. The mechanical anisotropy was shown to be spectacular, with the storage moduli in perpendicular directions differing by as much as 2 orders of magnitude.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.