(138b) Microstructure and Rheology of Associative Soft Particles Glasses

Soft particle glasses (SPGs), such as associative microgels, provide a wide range of applications under shear flow due to their tunability of physical properties and unique rheology. In practice, the associative submicron microgels are functionalized with alkyl groups, which are responsible for short-range attractive forces. Therefore in a jammed state, there is a competition between the attractive and repulsive forces. Experimentally it is observed that the strength of the attraction can be tuned with the length of alkyl chains, and in contrast with the repulsive SPGs, these suspensions show flow heterogeneities under shear flow. Here we combine the three-dimensional (3-D) particle-dynamics simulation with the JKR model, which accounts for the attractive forces between the particles, to build a 3-D simulation technique for describing the dynamics of jammed attractive microgels. Simulations tools are used to predict the rheology of these suspensions with different attraction strengths under steady shear flow. At low shear rates, these suspensions exhibit a yield stress and at an intermediate shear rate, the shear stress plateaus for several decades of applied shear rate, which confirms the existence of flow heterogeneities as seen in the experiments. Simulations are used to characterize the origin of the heterogeneities by characterizing the relaxation times corresponding to cage opening and cage association and connect the microstructure and macroscopic properties of attractive microgels.