Droplet evaporation and de-pinning in rectangular microchannels

Experimental and numerical studies are presented for evaporation of micro-droplets of deionised (DI) water and toluene on lead zirconate titanate (PZT) substrates. The microchannels are fabricated with SU-8 2025 and 2075. The effects of channel width and depth on the evaporation and de-pinning rates of embedded micro-droplets are presented and compared for both fluids. The study reveals a partially hydrophobic nature of SU-8/PZT microchannel to DI water and a complete wetting when toluene is used as the droplet. The rate of evaporation of toluene is about double the rate of evaporation of DI water. Comparisons of the rates of evaporation and de-pinning show that the channel width has a larger effect on evaporation than the depth of the channel. The equivalent contact angle of the pinned film and bulk fluid compensated for the evaporation of the droplet. Surface roughness was also shown to have a significant effect on the pinned film in the rectangular microchannels.