Pattern Formation in Drying Drops of Polystyrene/Water nanofluids

We study the pattern formation and the evaporation dynamics of drying drops of polystyrene/water based nanofluids with concentrations ranging from 0.01{\%} to 6{\%}. Cracks formation is evidenced to depend on the nanoparticles concentration. The dynamics of evaporation is recorded using an electronic balance with an accuracy of 10$\mu $g. A top view recording enables to analyze the pattern formation in relation with the mass evolution. We determine several key parameters such as the time of evaporation, the wetting diameter, the final solid deposition diameter, the number and the spacing of the cracks. We evidence a ring formation above a critical concentration. We evidenced by change of the surrounding humidity in the range of 10 to 90{\%} that this pattern remains constant. The pattern formation is influenced by the liquid phase evaporation dynamics but only depends on the concentration in nanoparticles. These results are of great interest regarding the formation of droplets in several areas such as inkjet printing, pharmacology...