A Universal Way to Manipulate Droplet via Light‐Fueled Thermocapillary Convection

Abstract Droplet manipulation plays an important role in scientific research and applications, such as microfluidics and microreactors. Among various driving forces, light‐induced thermocapillary convection is a good candidate for propelling liquid droplets. Until now, photothermal additives that convert light into heat have been used as an essential component for droplet manipulation. However, additive‐based droplet manipulation relies on inefficient heat transfer and can be applied to limited surfaces and/or droplets. Herein, a new way to manipulate droplets is introduced, directly powered by mid‐infrared (MIR) light irradiation. Liquids, such as water and alcohol, exhibit high absorption coefficients for MIR light, efficiently converting it into heat. By using this phenomenon, the MIR laser is applied to realize thermocapillary convection. Liquid molecules at the outer surface of the droplet can spontaneously generate heat fueled by MIR laser, so that powerful thermocapillary convection can be generated within milliseconds. This simple yet effective thermocapillary convection enables highly efficient, controllable, and precise droplet manipulations. No additional additives and/or complicated substrates are required, allowing the method to be versatile for most kinds of liquid droplet and liquid repellent surfaces. Additionally, it is very advantageous for microreactor applications because it does not require a purification process to remove additives.