Motion behaviors of droplets containing Au nanoparticles on a superhydrophobic laser-induced graphene surface

Abstract

The movement of nanoparticle-containing droplets on solid surfaces significantly affects the distribution of the nanoparticles and is of great interest in the fields of two-phase separation, biosensing detection, inkjet printing, and microarrays. There has been little research on the initiation and motion behaviors of colloidal droplets containing nanoparticles on superhydrophobic surfaces. Here, we prepare superhydrophobic laser-induced graphene (LIG) surfaces with excellent depinning effects using an extremely simple method and explore the formation mechanism of the depinning-LIG surfaces. The reduction of nano-graphene fibers and the increased hydroxyl group ratio after alcohol modification further enhance the hydrophobic properties of depinning-LIG, reducing its surface adhesion. The initial and continuous motion of droplets containing Au nanoparticles (AuNPs) on these superhydrophobic surfaces under airflow is studied using high-speed microscopy. The coupling effects of the droplet size, surface properties, airflow velocity, and nanoparticles on the droplet motion behaviors are analyzed. The dimensionless parameter G is incorporated to obtain the partition diagram of AuNP droplet motion behaviors on depinning-LIG surfaces, which delineate the critical conditions for droplet “oscillation,” “initiate sliding,” and “continuous rolling” as a function of system parameters. For AuNP droplets, the viscous force Fγ,p exerted by the nanoparticles on the contact line significantly affects the droplet movement behaviors. In addition, a mathematical model about the competition of dynamic forces and resistance is established to describe the motion of AuNP droplets, and the critical conditions for different motion behaviors of the droplet are clarified to guide practical applications.