EFFECT OF THE WETTABILITY ON THE IR LASER PHOTOTHERMALLY INDUCED PHASE CHANGE IN MICROCHANNELS

In this paper, the IR laser photothermally induced phase change characteristics in the microchannels with different wettabilities were studied using visual experiments. The hydrophobic microchannel was obtained by the hydrophobic nature of the PDMS material while the hydrophilic microchannels were obtained by the inert gas plasma surface treatments. Effects of the contact angle, laser power and spot position were investigated. It is interesting to find the change of the wettability and laser power could alter the phase change behaviors. The hydrophobic microchannel showed the interface advancement at low laser power and the liquid slug formation accompanying with the interface receding at high laser power. For less hydrophilic microchannel, the liquid slug formation accompanying with the interface receding was observed at low laser power while the sole interface receding was observed at high laser power. For more hydrophilic microchannel, the sole interface receding was observed for both low and high laser powers. Besides, it was also found that increasing the distance between the initial interface location and laser spot led to the increased thermal resistance, lowering the evaporation rate and thereby the above-mentioned effect.