Wetting properties of patterned silicon microchannels with tunable surface energy using layer-by-layer nano self-assembly

The wettability of patterned silicon microchannels with tunable surface free energy through coating hydrophilic TiO₂ nanoparticles using layer-by-layer (LbL) nano self-assembly technique is presented in this paper. Wettability of microchannels is tested by measuring the contact angle of a water droplet on the substrate. The capillary rise rate is tested by measuring the front location of liquid on the silicon microchannel surface laid on a 45 degree inclined platform. It is found that the silicon microchannels with tunable surface free energy have super-hydrophilic wettability, and demonstrate powerful capillary. For the silicon microchannels 200 μm wide, the liquid front can move up 40 mm in approximately 3 second. Fourier transformed infrared spectroscopy (FTIR) and X-ray photoelectron spectroscopy (XPS) reveal the generation of -OH radicals after coating TiO₂ nanoparticals, verifying that the -OH radicals have a strong effect on the hydrophilicity. The super-hydrophilic patterned microchannels suggest potential applications to microfluidic systems and heat diffusion systems based on liquid surface tension.