Femtosecond Laser Interference Micro-patterning on Mold Surface to Improve Hydrophobicity for Microfluid Applications

Fluidic flow in micro-channels is driven by capillary filling actuation mechanism. Therefore, surface hydrophobicity plays a significant role in controlling the fluidic flow. Surface hydrophobicity can be tuned by depositing hydrophobic material onto the surface, or by creating surface micro-/nano-textures that follow Cassie-Baxter model (hydrophobic). To facilitate fluidic flow in a microchannel, it is critical to design and create superhydrophobic surfaces with high contact angle and low contact angle hysteresis, which require accurate control of two-scale micro-/nanostructures. In this study, we propose to use laser interference to create deterministic micro- and or nano-level patterns on a metal mold surface. Femtosecond laser is chosen due to its high machining precision and minimum heat-affected zone. The surface structures are characterized by optical and scanning electron microscopy. The surface wettability is analyzed by measuring surface water contact angles. Through hot embossing, the surface structures are replicated onto surfaces of polymer microfluidic channels. The proposed method is shown to be effective and easy to implement for microfluidic applications.