Mixed liquids can be separated from each other by allowing two immiscible solvents to flow against each other. However, this only works if the density and flow behavior of the two liquids are matched. During their experiments with a self-built apparatus, Felix Engelmann, Carina Lämmle and Simeon Völkel (from left to right) came across the problem of phase retention: it is difficult to hold back one of the liquids while the other flows over it at a defined speed. The young scientists then investigated the change in flow behavior in a rotating glass screw as a function of rotation, screw diameter and material properties and were awarded the Federal Minister of Education and Research's prize for the best interdisciplinary work. They want to transfer the findings from the analysis to their apparatus in order to improve the separation process.