Propagation of a chemo-mechanical phase boundary in polyacrylate gels

The competition between mono- and divalent counterions in polyelectrolyte gels can lead to reversible transitions between swollen and collapsed phases. In this study, we investigate the emergence of a propagating boundary that separates the two phases in cylindrical polyacrylate gels, where it moves along the gel's longitudinal axis. We emphasize the distinction between an overall calcium-induced contraction and the axial progression phenomenon and use an object detection algorithm to determine the boundary propagation rate. Additionally, we investigate how calcium concentration, external voltage, and gel diameter influence the formation time and propagation velocity of the phase boundary. Our findings reveal that an increased calcium concentration in the adjacent bath, the application of an external voltage, and a decreased gel diameter contribute to a shorter formation time and a higher propagation velocity of the phase boundary. These results provide important insights into the complex dynamics of phase boundaries in cylindrical polyelectrolyte gels.