Newtonian coalescence in colloidal and non-colloidal suspensions

TL;DR

This study investigates coalescence dynamics in colloidal and non-colloidal suspensions, revealing flow-dependent thinning and extending the Newtonian coalescence universality to complex fluids through experiments and a theoretical model.

Contribution

It extends the Newtonian coalescence law to complex fluids with viscoelastic properties using experimental data and a theoretical model based on Ostwald-de Waele law.

Findings

Flow-dependent thinning response observed in suspensions.

Newtonian coalescence exponent $b=0.5$ extended to complex fluids.

Theoretical model supports the existence of arrested coalescence.

Abstract

Coalescence event in pendant and sessile drop is distinguished by the formation and evolution of the liquid bridge created upon singular contact. The bridge radius, $R$, is known to evolve as $R\sim t^b$, with power-law exponent, $b$, signifying the dominant governing forces. In this work, we experimentally explore the phenomenon in sub-classes of complex fluids namely, colloidal and non-colloidal suspensions that have particle hydrodynamic interactions as origin of viscoelasticity. Our observations suggest that such fluids have flow dependent thinning response with finite elasticity in shear flows but negligible in extensional flows. 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 constitutive law. Finally, we utilize this theoretical model to inspect the existence of arrested coalescence in generalized Newtonian fluids.