The effect of gold nanoparticles on the physical and chemical properties of water after drops fall from a height of several meters and hit from a hard surface

Introduction Nanofluids are known to be highly effective in droplet coolers. It is also known that the presence of nanoparticles in a water droplet significantly alters the nature of the droplet’s spreading after impact with a solid surface. The physics of this phenomenon is unclear, although it is known that the droplet viscosity, as well as the temperature and properties of the substrates on which the droplets impact, have an effect. It has been hypothesized that the observed phenomenon may be based on changes in the physicochemical properties of the liquid (pH, temperature, gas phase distribution, concentration of molecular oxygen and reactive oxygen species) in the presence of nanoparticles. Therefore, the aim of this work was to study the effect of gold nanoparticles on the physicochemical properties of water after droplets impact with a solid surface. Methods Laser ablation in liquid, spectroscopy in the visible and ultraviolet range, DLS, TEM, luminescence, thermal oximetry, measurement of the concentration of hydrogen peroxide and hydroxyl radical, inhibitory analysis. Results Luminescence of water droplets and aqueous colloids of gold nanoparticles, arising when the drops fall from a height onto a solid surface, has been detected. It has been shown that the luminescence intensity increases with an increase in the impact force; an increase in the concentration of gold nanoparticles; an increase in the concentration of molecular oxygen dissolved in the liquid. After water droplets fall from height of several meters onto solid surface, the concentration of dissolved molecular oxygen in them decreases, the intensity of such degassing increases with an increase in the concentration of nanoparticles and the fall height. The phenomenon is largely due to the release of gas into the atmosphere due to the formation and floating up to the liquid-gas boundary of large gas bubbles, and to a lesser extent due to an increase in the droplet temperature upon impact. It has been shown that ROS generation is observed upon droplet impact on solid surface. The intensity of ROS generation depends on the fall height of the droplets and the content of nanoparticles in the droplets. The process that triggers ROS generation is probably the transition of oxygen molecules dissolved in water from the triplet to the singlet state. Discussion The processes we have discovered may bring us closer to understanding the mechanisms underlying the anomalous change in the pattern of droplet spreading after impact on a solid surface in the presence and absence of nanoparticles.