Traveling Coacervate Band Through a Charged Gel

It is well known that coacervates can be formed when polycation solutions and polyanion solutions mix at appropriate pH, ionic strength, and polymer concentration. In this work, we experimentally find a novel coacervation phenomenon where a polyanionic gel is exposed to a solution of polycations. For the system of poly(acrylamide-co-sodium acrylate) and poly(allylamine), we have discovered that the coacervates would initially travel through the gel and form a thin band in the middle of the gel. This band subsequently gives rise to a second band which grows in the opposite direction. Curiously, these two bands subsequently result in a third band which forms between the two pre-formed bands. The rich details on the features of these bands and their growth kinetics will be presented.