Rapid deposition and precise control of particles are crucial for various applications, including microfluidics, therapeutics, and nanomaterials. Controlling particle deposition to suppress the coffee ring effect still remains challenging due to the droplet evaporation kinetics, thermal Marangoni flow, and solute Marangoni flow. Here, we propose changing the heating mode from surface heating to bulk-phase heating by utilizing laser-induced evaporation of plasmonic-containing droplets. We found that the evaporation rate on the hydrophobic substrate exceeds that on the hydrophilic substrate by an order of magnitude, reaching approximately 0.03 μL/s compared to 0.003 μL/s on the hydrophilic surface. Infrared thermal imaging and numerical analysis show that there is competition between thermal and solutal Marangoni flows inside the plasmonic droplet. On hydrophilic substrates, solutal Marangoni flow is inhibited in the late stage of evaporation due to the pinning effect with thermal Marangoni flow toward the contact line dominating. In contrast, hydrophobic substrates are dominated by solutal Marangoni flow toward the laser center throughout the evaporation process. Laser-induced evaporation of plasmonic-containing droplets on hydrophobic substrates enables rapid particle deposition control. These results offer a new approach for highly tunable and precise control over the preparation of functionalized patterns.
Lei et al. (Tue,) studied this question.