A hybrid microfluidic chip with electrowetting functionality using ultraviolet (UV)-curable polymer

Electrowetting (EW) is widely used in digital microfluidics for the manipulation of drops sandwiched between two parallel plates. In contrast, demonstrations of closed microfluidic channels enhanced with EW functionality are scarce. Here, we report a simple, low-cost method to construct such microchannels enclosed between two glass plates, each of which comprises electrodes and insulating layers. Our method uses soft imprint lithography with thiolene precursors to design the channel geometry. UV exposure is used to seal the chips permanently and a silanization treatment renders all inner channel surfaces hydrophobic. Compared to earlier polydimethylsiloxane-based designs, this method allows us to make microchannels with smaller dimensions (down to 10 microns), lower aspect ratios (down to height/length = 1/10), and symmetric electrodes both on the top and the bottom of the channel. We demonstrate the new capabilities with two examples: (i) EW-enhanced drop generation in a flow focusing geometry allows precise and continuous control on drop diameter in the range approximate to 1-15 microns while maintaining monodispersity; (ii) EW allows tuning of the excess water pressure needed to displace oil in a microchannel, leading to spontaneous imbibition at EW number eta > 0.89.