Water Freezes at Near-Zero Temperatures Using Carbon Nanotube-Based Electrodes under Static Electric Fields
Although static electric fields have been effective in controlling ice nucleation, the highest freezing temperature (Tf) of water that can be achieved in an electric field (E) is still uncertain. We performed a systematic study of the effect of an electric field on water freezing by varying the thickness of a dielectric layer and the voltage across it in an electrowetting system. Results show that Tf first increases sharply with E and then reaches saturation at −3.5 °C after a critical value E of 6 × 106 V/m. Using classical heterogeneous nucleation theory, it is revealed that this behavior is due to saturation in the contact angle of the ice embryo with the underlying substrate. Finally, we show that it is possible to overcome this freezing saturation by controlling the uniformity of the electric field using carbon nanotubes. We achieve a Tf of −0.6 °C using carbon nanotube-based electrodes with an E of 3 × 107 V/m. This work sheds new light on the control of ice nucleation and has the potential to impact many applications ranging from food freezing to ice production.