Dynamics of viscoelastic fluid droplet under very low interfacial tension in a serpentine T-junction microchannel

摘要

Droplets of viscoelastic fluid were generated in silicone oil using a microfluidic T-junction device, and their intrinsic dynamics were studied. The viscoelastic fluid used was a dilute aqueous solution of cetyltrimethylammonium chloride (CTAC) with sodium salicylate (NaSal) at the same mass concentration as CTAC. The surfactant greatly lowered the interfacial tension between the silicone oil and surfactant-laden droplet and also introduced elasticity to the aqueous solution. The generated droplets experienced extension-shearing mixed kinematics as they moved along the confined microchannel, showing distinct morphological evolvement compared with those of Newtonian fluids and polymeric solutions under normal magnitudes of interfacial tension. With surfactant additives in the dispersed phase, the droplet tail streaming was composed of tiny satellites at the rear (upstream) of the droplet. The emergence of tails depended on the physical properties, such as the flow rate ratio, of the two fluids. This phenomenon indicates a new regime for the deformation of soluble-surfactant-laden droplets governed sequentially by three different processes of dynamic shearing, elongation and interfacial instability.