Figure 3: Oil collection on PDMS needle arrays.

(a) Schematic of the collection device. When the oil–water mixture flowed through the needle array, the oil in the mixture was collected by the conical needles, and the pure water flowed towards the other end of the device. (b) Oil–water mixture. (c) Collected oil. (d) Separated water, nearly no visible red oil was present. To facilitate observation, Oil Red O is added to the oil.