Bimodal suspensions: semi-empirical prediction of viscosity and linear viscoelastic response

Understanding the rheology of highly concentrated bimodal suspensions presents a longstanding challenge due to the complexity of particle interactions. This work develops a novel semi-empirical model to accurately predict the viscosity across a wide range of volume fractions in bidisperse systems. The model uniquely captures the viscosity deviation caused by many-body hydrodynamic effects and interparticle contact forces. Good agreement is obtained between model predictions and experimental data from dilute to highly concentrated region. The infinite viscosity at jamming further verifies model validity. Systematic studies reveal the significant impact of key dispersity parameters—diameter ratio and weight fraction ratio of large-to-small particles—on viscosity and linear viscoelastic response. Optimal combinations of these parameters are shown to maximize maximum packing fraction and minimize viscosity. The model provides new physical insights into highly concentrated bimodal suspension viscosity and enables customized design of bidisperse suspensions over a wide concentration range.