Flexible fabrication of lipophilic-hydrophilic micromotors by off-chip photopolymerization of three-phase immiscible flow induced Janus droplet templates

Abstract

Self-propelled microparticles are promising for lots of applications ranging from analytical detection to water treatment. Herein, we present an effective approach to fabricate lipophilic-hydrophilic micromotors via the photocuring of three-phase immiscible flow induced droplet templates. In the microfluidic system, two immiscible inner fluids, the lipophilic 1, 6-Hexanediol diacrylate (HDDA), and the hydrophilic poly (ethylene glycol) diacrylate (PEGDA), are simultaneously injected into a theta-shaped cylindrical capillary from two separate inlets, and they are emulsified into Janus drops when encountering the outer immiscible silicone oil. Because of the immiscible feature of droplet templates, off-chip photopolymerization strategy has been used, which can significantly decrease the blocking chance of microdevice. And also, the lipophilic-hydrophilic structure of droplets is convenient for the loading of cargos with different characteristics. More importantly, the size and configuration of droplet templates can be flexibly regulated by changing the flow rates of three different phases. Accordingly, multifunctional micromotors can be fabricated by adding different nanoparticles and materials into the HDDA or PEGDA phase first and then photocuring the droplets. Taking the bubble-propelled micromotors for example, we prepare microswimmers by loading Ag, TiO2 and Fe3O4 nanoparticles into the PEGDA phase. The swimming behaviors of micromotors in H2O2 solution are systematically investigated, finding that the proportion of PEGDA phase and the concentration of H2O2 both positively affect the moving speed. Furthermore, the applicability of motor particles on water treatment is successfully demonstrated by using neutral red solution as the model pollutant. And the micromotors can be recycled using magnets after the catalytic degradation process. Therefore, this micromotor generation technique and this kind of micromotor can be attractive for many applications.