Frictional contact network in dense suspension flow

Dense suspensions often exhibit discontinuous shear thickening (DST) and shear jamming (SJ). A consensus has emerged that this behavior is driven by a transition from lubricated, unconstrained particles to system-spanning frictional contact networks (FCNs) responsible for enhanced flow resistance. Using a network framework, we quantify FCN topology and show that suspensions with only sliding friction form highly branched FCNs with multi-contact nodes and compressive force chains needing orthogonal support. In contrast, rolling resistance reduces branching and increases rattlers, enabling long, linear chains without orthogonal support. This transition explains why rough particles show DST and SJ at lower packing fractions. Rolling resistance alters the jamming packing fraction and FCN, leading to a revised mechanical stability picture for rough particles. Our findings reveal that suspensions with similar viscosities can exhibit fundamentally distinct FCNs, depending on frictional constraints, highlighting limitations of mean-field models and establishing a framework connecting microscale constraints to macroscale rheology.