A blue-dyed material going across the interface while a yellow due material does not. The difference is that treble has a positive charge and the yellow is negatively charged.
The researchers used two polymer aqueous solutions, one of polyethylene glycol (PEG) and water, the other dextran and water, with different electrical charges, that can be combined but do not mix. They say it’s a classic example of coacervation, where the solution undergoes liquid-liquid phase separation and forms two separate domains, like the non-mixing wax-and-water in a lava lamp. Courtesy UMass Amherst/Russell Lab