Band Formation in Coacervate Gels

By experimentally investigating the invasion of a polyelectrolyte into a charged hydrogel, we report a novel coacervate band formation deep inside the gel, unlike in equilibrated coacervate gel composites. Using turbidimetry, static and dynamic light scattering, and rheology, we have monitored the beginning location and time of birth of the coacervate band inside the gel, and its time-evolution. Once a band is born, with time, it becomes more intense and broadens downstream with the permanent localization of the initial beginning location. Even more remarkably, at later stages of the band’s life, it forms daughter bands upstream, suggesting redistribution of the guest molecules at late times. The various quantitative features of the band depend crucially on the initial concentration gradient of the invader. Our observations open a new direction in coacervate gel systems under nonequilibrium conditions.