Effect of DLVO interactions on the rheology and microstructure of non- Brownian suspensions

JH Wang and DY Pan, ACTA MECHANICA SINICA, 39, 322469 (2023).

DOI: 10.1007/s10409-023-22469-x

The macroscopic rheological properties of suspensions are often inextricably related to changes in their microstructure, and a number of experimental studies have demonstrated the significant influence of DLVO (Derjaguin-Landau-Verwey-Overbeek) interactions, namely microscopic repulsive and attractive forces due to surface charge on particles in suspensions, on the microstructure of suspensions, especially on cluster formation. In this study, the rheological properties of non-Brownian suspensions and their microstructures are investigated by numerical simulations combining DLVO interactions with hydrodynamics and frictional contacts. Di fferent mechanisms have been identified to account for diverse rheological responses of repulsive and adhesive suspensions, revealing a significant association between the evolution of particle clusters and suspension rheology. In repulsive systems, competitions between repulsive and hydrodynamic forces and the resulting change in the distribution of minimum particle separation are responsible for the first shear thinning at low shear rates. Shear thickening is observed at high shear rates and is dominated by particles contacts. Enhancing attractive forces give rise to the viscosity of the suspensions while obscuring shear thickening, and particles make contacts even at the first shear thinning conditions. The second normal stress di fference exhibit similar evolution with viscosity while the first normal stress di fference is mainly dominated by fluctuations. Microstructure analysis shows frictional clusters appear in repulsive suspensions with growth in both quantity and size as shear rate increases. Clusters in strongly adhesive suspensions, on the other hand, break into smaller ones, resulting in a viscosity reduction. The calculation of the shape anisotropy indicates that frictional clusters in repulsive suspensions tend to expand uniformly in simulation box whereas at high attractive strength, clusters deform more cylindrical when strongly sheared. Our studies in microstructure can fundamentally help in bridging the gap between microscale evolution and macroscale rheological responses, thus contributing to the foundation of the constitutive model of non-Brownian suspensions.

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