Suspensions exhibit scale-dependent behavior: while they can be treated as homogeneous viscous fluids at macroscopic scales, the presence of discrete particles introduces local heterogeneity that becomes significant during dynamic processes like droplet pinch-off. In this study, high-speed photography is used to explore the thinning and pinch-off dynamics of Newtonian suspensions laden with monodisperse, neutrally buoyant particles. By systematically varying particle volume fraction (ϕ) and diameter (ds), we analyze the thinning process and identify two critical neck thicknesses, h* and h′, which delineate transitions between the equivalent fluid regime, the dislocation regime, and the interstitial fluid regime. The results show that the oscillations of thinning rate are progressively suppressed at higher-particle concentrations yet become increasingly amplified for larger particles, especially when particle entrapment perturbs the filament. We demonstrate that the onset of heterogeneous thinning is associated with particle dislocation and concentration fluctuations, leading to an acceleration in neck thinning. The dislocation regime exhibits a tunable power-law thinning behavior h(t) ∼ tc−tα, where α lies between 0.5 and 1, depending on particle concentration and size. Furthermore, the threshold thickness h* is quantitatively predicted using a theoretical model based on capillary–viscous energy balance, and good agreement with experimental data was achieved. Our findings provide new insights into the multiscale mechanics of suspension breakup and offer predictive tools applicable to a wide range of technologies, including inkjet printing and microfluidics.
An et al. (Sun,) studied this question.