Studio della dinamica di trasporto di gocce in canali microfluidici

Systems of drops in annular flows are common in nature and many applications that employ such phenomena are under development. This thesis presents an experimental work regarding the velocity of medium sized water-in-oil droplets in micrometric circular capillaries (0.3 um of diameter) as a function of different parameters – length of the drop (long from 1 to 15 tube diameters), viscosity ratio, surface tension, presence of surfactants. Velocity depends on the capillary number with a power law, whose exponent depends on both the droplet lenght and the superficial tension, but numerically near to 1/3; surfactants are proven to change the system’s dynamics due to the presence of Marangoni forces, which slow down droplets.