Sub-newtonian coalescence in polymeric fluids

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MTech (Res); 2022; Mechanical engineering

Droplet coalescence is a thermodynamic equilibration process driven by surface energy minimization. The physics of this phenomenon is characterized by the temporal evolution of a liquid bridge formed upon the proximate approach of two droplets. This phenomenon is ubiquitous, manifesting in processes linked to life like those in raindrop formation, growth of tumor cells, and industrial processes like those in combustion, spray paintings, and coatings. Despite these universal occurrences, studies on the coalescence of complex fluid droplets remain scarce in the literature. Unlike Newtonian fluids, complex fluids have signature micro-structures that can result in a wide range of responses depending on external perturbations making a unified model elusive. Such diversity in micro structures and flow behaviors have resulted in classifying these in sub-classes ranging from polymers to suspensions. But there has been a recent surge in studies investigating coalescence dynamics in macromolecular-based micro-structure fluids, i.e., polymeric fluids. However, a detailed work on developing a theoretical framework for coalescence in complex fluids remain unknown. Here in this thesis we propose such frameworks for polymers, suspensions and dispersions. Further based on our observations for polymeric fluids, we propose the existence of new coalescence regime, namely the sub-Newtonian regime with arrested coalescence as its limiting case.