Microbubble Generation Using Carbon Nanotubes Heating Elements

The generation of microbubbles using localized microwatt heating of carbon nanotubes (CNTs) is presented in this paper. Dielectrophoretic force is used to form CNTs between micrometal electrodes. The improvement for our CNTs heater is that a thin aligned SiO₂ film is employed to fix contact between metal electrodes and the CNTs, in order to decrease the heat loss from metal electrodes. The localized heat generated by CNTs is provided by a dc current that induces a temperature increase due to resistive heating. The bubble diameter grows as the transduction of electrical energy into Joule heating across the CNTs heater. We conduct experimental and theoretical analysis to estimate the surface temperature of a typical CNTs heater when bubble generation occurs. Similar to typical boiling phenomenon, the micron-scale bubbles are generated using CNTs as the nucleation site. Our experiments show that the instantaneous power required to generate bubbles is less than ~113 μW, which is only ~1% to 10% of the metal heaters, as reported by other researchers. Experiments also show that total input energy could be as small as 0.3~5 mJ to initiate bubble generation. As the maximum diameter of generated bubbles is around 400 μm and the speed of the expansion of the diameter is controllable by adjusting current input, this novel CNTs heating elements could be used in various application areas that require low-power consumption, such as hand-held ink-jet printing or heat-convection-based micromotion sensors.