On-Demand Capture and Release of Organic Droplets Using Surfactant-Doped Polypyrrole Surfaces

In this paper, we demonstrate the controlled capture and release of dichloromethane (DCM) droplets on dodecylbenzenesulfonate-doped polypyrrole (PPy(DBS)) surfaces in an aqueous environment. The droplets captured on oxidized PPy(DBS) surfaces were released on-demand via a reduction process at ∼0.9 V, with controlled release time and droplet morphology. The release time of an entire droplet (2 ± 1 μL) was proportional to the thickness of the PPy(DBS) coating, increasing from 11.5 to 26.3 s for thicknesses ranging from 0.6 to 5.1 μm. The droplet-release time was also affected by the redox voltages, and among the tested redox voltages, the fastest release was achieved at -0.9/0.1 V. The PPy(DBS) surfaces with larger thicknesses were more durable for the droplet capture and release. The droplets were more rapidly released from PPy(DBS) surfaces with increased surface roughness ratios, such as 6.0 s on a micropillared surface and 10.3 s on a meshed surface, as compared to 14.6 s on the 1.8 μm thick PPy(DBS) surfaces coated on frosted-glass substrates (i.e., with random microstructures). The release of a single droplet was achieved by increasing the underwater oleophobicity of PPy(DBS) surface via O₂ plasma treatment.