Evaluation of Microgap Control of Needle-Type Dispenser for Precise Microdroplet Dispensation

Microdroplet dispensation is required in current systems and industrial equipment. However, dispensing microdroplets from high-viscosity liquids using dropon-demand inkjet technologies is difficult. Therefore, a needle-type dispenser comprising a thin needle and glass capillary containing the liquid to be dispensed has been developed for microdroplet dispensation. When the needle passes through the capillary, a droplet of the liquid adheres to the needle tip. A microdroplet can be transcribed by bringing the needle-tip droplet into contact with the target surface. The needle-type dispenser can dispense sub-pico-liter droplets with viscosities of several hundred pascalseconds at a throughput of a droplet per 1 s. When a microdroplet is dispensed, a gap between the needle tip and target surface may be formed. Droplet volumes depend on the dispensing gap, and unstable if the gap fluctuates. Thus, a contact-detection method for the needle-tip droplet and target surface is proposed where the needle is vibrated by a piezoelectric actuator using a leaf spring. The needle-vibration characteristics depend on conditions between the needletip droplet and target surface. Contact of the needletip droplet with the target surface can be detected by the needle-vibration characteristics. The dispensing gap can thus be kept constant to dispense precise droplet volumes. In this study, the needle-vibration characteristics of the fabricated mechanism were evaluated experimentally for needle diameters of 500 and 100 µm. The needle-vibration displacements decreased depending on the dispensing gap for liquids with viscosities of 0.1 to 100 Pa•s.