Tuning the rheology and microstructure of suspensions in the glass transition regime using attractive interactions

Near the glass transition, a monodisperse suspension of hard-sphere particles under shear exhibit string-like ordering along the flow direction and hexagonal patterns perpendicular to the flow. These patterns reduce suspension viscosity, resulting in non-monotonic viscosity behavior as a function of volume fraction in dense regimes. Using Stokesian dynamics simulations, we explore the control of these patterns via attractive interactions modeled by a van-der-Waals-like potential. The ratio of shear to attractive forces is defined by the Mason number. At high Mason numbers (shear-dominant regime), shear-ordering patterns emerge between 48% and 58% volume fractions, with a time-dependent viscosity decrease known as thixotropy. At moderate to low Mason numbers, attractive forces disrupt the formation of shear-ordering structures, preventing viscosity reduction. In these regimes, viscosity increases monotonically with volume fraction and follows the power law. At very low Mason numbers, strong attractions cause significant viscosity increase due to the formation of an attractive glass. These findings manifest the ability to tune the rheology and microstructure of these systems through the interplay of attraction and shear.