Life and death of colloidal bonds control the rate-dependent rheology of gels

Colloidal gels exhibit rich rheological responses under flowing conditions. A clear understanding of the coupling between the kinetics of the formation/rupture of colloidal bonds and the rheological response of attractive gels is lacking. In particular, for gels under different flow regimes, the correlation between the complex rheological response, the bond kinetics, microscopic forces, and an overall micromechanistic view is missing in previous works. Here, we report the bond dynamics in short-range attractive particles, microscopically measured stresses on individual particles and the spatiotemporal evolution of the colloidal structures in different flow regimes. The interplay between interparticle attraction and hydrodynamic stresses is found to be the key to unraveling the physical underpinnings of colloidal gel rheology. Attractive stresses, mostly originating from older bonds dominate the response at low Mason number (the ratio of shearing to attractive forces) while hydrodynamic stresses tend to control the rheology at higher Mason numbers, mostly arising from short-lived bonds. Finally, we present visual mapping of particle bond numbers, their life times and their borne stresses under different flow regimes. Understanding the origin of transient spatio-temporal response of colloidal gels is an essential aspect for their application. Nabizadeh and Jamali demonstrate the coupling between the lifetime of colloidal bonds and the rheology from computer simulations on steadily sheared model gels.

Automated summary

The study explores the coupling between the kinetics of colloidal bonds and rheological response in attractive gels under different flow regimes. It reveals the importance of interplay between particle attraction and hydrodynamic stresses in understanding the physical basis of colloidal gel rheology. The research also presents visual mapping of particle bond dynamics and stresses under various flow conditions.