Freezing of complex fluids
When a drop of water is deposited on a cooled surface allowing freezing, such as a Peltier module, the propagation of the solidification front leads to the formation of a tip at the top. This singularity is the result of the lower density of ice compared to liquid water as well as the angles formed between liquid, ice and air. Here, the researchers compared the shape of the tips for drops of pure water to other drops with low solute concentrations, and they noticed measurable variations in the angles formed. The photograph illustrates the difference between a drop of pure water on the left and a drop of water containing a surfactant on the right. We also observe that crystals grow at the summits by condensation. These results show the significant importance of impurities on morphologies in glaciation processes, which can be used for the purpose of global characterizations of water purity.