Newtonian coalescence in colloidal and noncolloidal suspensions

Coalescence event in pendant and sessile droplets is distinguished by the formation and evolution of the liquid bridge created upon singular contact. For Newtonian droplets, the bridge radius, R, is known to evolve as R similar to t (b), with universal values of the power-law exponent, b, signifying the dominant governing forces. However, recent works on different subclasses of rheologically complex fluids comprising of macromolecules have highlighted the effects of additional forces on coalescence. In this work, we experimentally explore the phenomenon in distinct subclasses of rheologically complex fluids, namely, colloidal and noncolloidal suspensions, that have particle hydrodynamic interactions as the origin of viscoelasticity. Our observations suggest that such fluids have flow-dependent thinning responses with finite elasticity in shear rheology but negligible elasticity in extensional rheology. Based on these, the study extends the Newtonian universality of b = 0.5 to these thinning fluids. Further, we fortify these observations through a theoretical model developed by employing Ostwald-de Waele's constitutive law. Finally, we utilize this theoretical model to inspect the existence of arrested coalescence in generalized Newtonian fluids.