la3014392_si_001.pdf (368.43 kB)
Discrete Electrostatic Charge Transfer by the Electrophoresis of a Charged Droplet in a Dielectric Liquid
journal contribution
posted on 2012-08-14, 00:00 authored by Do Jin Im, Myung Mo Ahn, Byeong Sun Yoo, Dustin Moon, Dong Woog Lee, In Seok KangWe have experimentally investigated the electrostatic
charging
of a water droplet on an electrified electrode surface to explain
the detailed inductive charging processes and use them for the detection
of droplet position in a lab-on-a-chip system. The periodic bouncing
motion of a droplet between two planar electrodes has been examined
by using a high-resolution electrometer and an image analysis method.
We have found that this charging process consists of three steps.
The first step is inductive charge accumulation on the opposite electrode
by the charge of a droplet. This induction process occurs while the
droplet approaches the electrode, and it produces an induction current
signal at the electrometer. The second step is the discharging of
the droplet by the accumulated induced charge at the moment of contact.
For this second step, there is no charge-transfer detection at the
electrometer. The third step is the charging of the neutralized droplet
to a certain charged state while the droplet is in contact with the
electrode. The charge transfer of the third step is detected as the
pulse-type signal of an electrometer. The second and third steps occur
simultaneously and rapidly. We have found that the induction current
by the movement of a charged droplet can be accurately used to measure
the charge of the droplet and can also be used to monitor the position
of a droplet under actuation. The implications of the current findings
for understanding and measuring the charging process are discussed.