Designing metafluids with multi-dimensional rheological properties: Dual shear thickening, rheopexy, and thixotropy in a single Fluid

The non-Newtonian rheology of dense suspensions enables transitions between states with widely varying viscosity. Conventional suspensions, however, have limited dynamic tunability and the shear-induced microstructures lack an extended lifetime. We report on suspensions in which the interplay of two distinct types of particle interaction, physical and chemical, leads to multi-dimensional rheological characteristics, encompassing dual shear thickening regimes, rheopectic, and thixotropic behaviors, all in the same fluid but across different stress ranges. These unconventional rheological properties represent metamaterial qualities, albeit for a fluid. Such metafluid retains a memory of its shear-induced microstructure, enabling applications in multi-functional energy damping systems that can be trained. We demonstrate this capability by training the suspension's stress response through repeated impact.