A new method for significantly reducing drop radius without reducing nozzle radius in drop-on-demand drop production

The lack of a simple method for generating drops whose radii (R-d) are much smaller than those (R) of nozzles which produce them has heretofore been a major limitation of the drop-on-demand technique. Therefore, the only reliable way to reduce R-d to date has been to reduce R. A new method is reported which allows an order of magnitude reduction in drop volume while using the same nozzle. It is shown that the key to forming drops with R-d<R is to judiciously control the capillary, viscous, and inertial time scales that govern the flow within the nozzle and the forming drop. The time scales are controlled in experiments by appropriately driving a piezoelectric sleeve surrounding a microcapillary tube, and the interplay between them is elucidated through computation. (C) 2002 American Institute of Physics.