Effect of width/height of the gap between piston and wall on the performance of a novel small volume emulsification device

Abstract

The concept of a small volume emulsification device developed by the authors is further studied in the present work. Following suggestions of previous work, five different piston plates with orthogonal edges are constructed to oscillate inside a small cube-shaped cell. The different pistons yield several combinations of gap width and height between the plates and the walls of the cell. Their performance is assessed by performing emulsification experiments over an extensive range of piston stroke frequency and emulsification time for a specific non-coalescing system (fixed oil fraction and surfactant concentration). The resulting droplet size distributions are estimated by microscopy images analysis and by phase separation observations. The combined information from these techniques is necessary in order to register the broad size range of droplets. A semiquantitative analysis of the flow field in the gap reveals that droplet breakage process starts at the laminar boundary layers developed between the piston and the cell walls and allows characterization of this field. A theoretical analysis for the mechanism of droplet breakup is presented. The analysis of experimental results demonstrates that four of the five tested piston plates are appropriate for emulsification regarding the generated droplet size distribution and the choice among them requires additional criteria, e.g. energy requirements.