(316k) Passive Single Droplet Dispensing Using Capillary on Ehd Method

Using electrohydrodynamic force is an alternative method of dispensing single droplet of various liquids. EHD method is predictable and controllable since it only uses electrostatic interaction as its driving mechanism. Unlike EHD jet, single droplet dispensing needs to be controlled before each process to maintain homogeneous droplet size. This process of controlling the initial state of EHD dispensing is one limit of the single droplet dispensing using EHD method.

In this work, capillary force was used to overcome this limit and to reduce the size of the total dispensing system. On the bottom reservoir capillary was installed vertically, lower than the equilibrium height of the liquid inside the capillary to maintain the same height even after dispensing. The use of external pump is needless since the surface force inside the capillary pulls the liquid to the equilibrium state. With high voltage, concave shape of the top of the liquid inside the capillary changes into convex shape which is defined by the applied voltage.

Stainless and glass capillary of 450ìm OD was used to dispense DI water on glass substrate. One sine pulse with 4kV of amplitude was used for one droplet. After 100 times of continuous dispensing, it can be concluded that passive dispensing with capillary has better uniformity even with the smaller operating size.