Regulating droplet impact dynamics of nanoparticle suspension: Phenomena, mechanisms, and implications

Droplet impact on solid substrates is a ubiquitous phenomenon in nature, agriculture, and industrial processes, playing a crucial role in numerous applications including self-cleaning, pesticide utilization, and inkjet printing. As a promising technique, adding nanoparticles into simple fluids to form nanofluids can effectively manipulate droplet impact behaviors. However, a comprehensive understanding of how nanoparticles modify the droplet impact dynamics, especially on the nanoscale, is still far from being fully explored. Hence, in this work, through the combined effort of molecular dynamics simulations and theoretical analysis, we elaborate on the influences of nanoparticles on droplet impact process. Using simple droplets as a control, we summarize four typical droplet impact modes and reveal how nanoparticles alter the impact behaviors of droplets, taking into account the key parameters including substrate wettability, impact velocity, volume fraction, and mass fraction of nanoparticles. We also demonstrate that with appropriate modifications, the theoretical/empirical models to predict the maximum contact diameter and the occurrence of breakup for simple droplets still hold to predict those of nanofluid droplets. Our findings and results enhance the understanding of the impact of nanoparticles on the droplet impact dynamics, with promising possibilities for various applications where regulating droplet impact behaviors is desired.