Droplet Evaporation on a Hydrophobic Photothermal Conversion Substrate

Use of the photothermal effect to control droplet evaporation shows great promise in various applications. Droplet evaporation initiated by direct photothermal conversion between light and fluid is limited by the interaction between the wavelength and fluid type. Here, we report laser-induced sessile droplet evaporation on a hydrophobic photothermal conversion substrate formed by embedding Ti2O3 particles into polydimethylsiloxane. Our results indicated that the photothermal conversion substrate could efficiently convert light energy into heat to enable droplet evaporation on it. Unlike droplet evaporation actuated by direct photothermal conversion, in which higher interface temperature was located at the laser projection region, the droplet evaporation on the photothermal conversion substrate showed higher temperature near the triple-phase contact line because of heat transfer from the substrate to the droplet and small heat transfer resistance resulting from small height at the edge. Due to the increased substrate temperature, the droplet evaporation on the photothermal conversion substrate could exhibit a relatively stable and long-term constant contact angle mode even under the localized heating effect. Moreover, by controlling the laser beam position, droplet evaporation could exhibit a directional long-term constant contact angle mode. The obtained results will be helpful for the design and operation of droplet microfluidics based on the photothermal conversion substrate.