Capacitive micro-oil detector with a nanotextured superhydrophobic/superoleophilic surface

In this study, we design and fabricate a capacitive micro-oil detector, and evaluate its performance. The surface of the detector, which is covered by nanotips, is superhydrophobic and superoleophilic. Because of the surface characteristics, while water cannot penetrate into the empty space between the two micro-spaced electrodes, oil is able to do so, leading to a change in the detector capacitance. Because of superoleophilicity enhanced by nanotips, nanostructured surfaces enable faster response times than nonstructured surfaces. We used the three primary types of marine fuel oils (heavy oil, crude oil, and diesel) to evaluate the performance of the fabricated oil detector. For oil films with thicknesses of 3μm or less, the capacitance increased almost linearly as the thickness increased, regardless of oil type. On the contrary, the capacitance remained almost constant for oil films thicker than 3μm. From highest to lowest, the measured capacitance is rated in the order heavy oil, crude oil, and diesel. Seawater did not seep into the microcavity of the fabricated detector for the depth of 1m. The fabricated detectors showed almost the same capacitances when detected and cleaned consecutively for 10 times. Furthermore, there was no surface damage during the 4-wk-long seawater immersion test.