Covalently Grafted Slippery Surfaces for Transport of Large-Volume Droplets and Bubbles

The directional transport and precise control of droplets and bubbles are crucial for future applications, but remain challenging due to complex fluid dynamics and application limits. In light of existing research on droplet manipulation, a MnO₂/carbon microsphere (MnO₂/Cs) covalently grafted lubricant-infused slippery surface (SPM) is designed for the manipulation of droplets and bubbles. The structure and morphology of the MnO₂/Cs are examined using X-ray diffraction (XRD) and field-emission scanning electron microscopy (FESEM), and the elemental composition and chemical bonds of the compounds are characterized by X-ray photoelectron spectroscopy (XPS), Raman spectra and Fourier transform infrared spectrometer (FTIR). The SPM with a sliding angle as low as 3° is prepared. On the SPM, the rapid transportation and precise control of small droplets can be achieved, with the transportation speed of 5 µL droplets reaching 1 mm s⁻¹ and the round-trip control of droplets also being feasible. The surface is capable of controlling the speed of a 100 µL droplet with a precision of 0.49 mm s⁻¹, while a 50 µL droplet can be directed with a load of 1 mg. Moreover, bubbles with a volume of 5 to 20 µL can also be transported.