Fig. 3 showed a schematic of EPD process of CNTs on carbon fibers
with or without ultrasonic. When the voltage of 20 V was applied,
rapid bubbling was observed at the region both the positive electrode
(carbon fibers) and negative electrode (graphite plate) because of the
electrolysis of water (decomposition voltage of 1.23 V). As shown
in Fig. 3(a), the tiny bubbles formed at the positive electrode had attached
themselves onto the surface of carbon fibers and until they
achieved a certain size they would gradually be separated away
from the electrode. If not removed immediately, the bubbles would
behave as insulation between the carbon fibers and aqueous CNTs suspension, which greatly reduced the number of deposition site.
However, in the presence of ultrasonic (Fig. 3(b)), the bubbles formed
were immediately dislodged and removed from the deposition sites
as a stream of bubbles. Meanwhile, ultrasonic ensured that bubbles
do not coalesce at the deposition location, thus avoiding trapped air
pockets that impede the deposition process