Motion of long droplets of liquid alkanes in a hydrophilic capillary due to a pressure drop

The velocity of a long droplet of an apolar liquid (octane, tridecane, tetr adecane) during its pressure-induced motion in a hydrophilic capillary fill ed (in its remaining part) with an aqueous solution of SDS (1.4 x 10(-4) M) and KCl (0.1 M) is experimentally studied and the results presented. The v ariable parameters are the pressure drop applied to the whole working capil lary, the radius of the capillary, and the length of the apolar liquid colu mn. The results are compared to known theoretical solutions. The experiment al results display a better agreement with the theory based on the film flo w model than with the theory based on the hydrodynamic lubrication mechanis m. However, the agreement is usually incomplete even for the former. In acc ordance with theoretical predictions, the experiment shows that the velocit y does not depend on the viscosity of the liquid in the droplet.