Figure 2.

Hierarchical PEC hydrogel microstructures. (a) Progression of the self-assembly of oppositely charged diblock polyelectrolytes (left) and triblock polyelectrolytes (right) in the structural progression of polyelectrolyte complex (PEC) hydrogels. Diblock bPEs form star-like micelles, while triblock bPEs form phase-separated gels. As the polymer concentration increases, diblock micelles become jammed, while triblock micelles begin to bridge into a percolated gel. Eventually, both diblock and triblock PE self-assemblies form ordered microstructures and undergo several order–order transitions. Scattering spectra of diblock (red) and triblock (blue) PEC self-assemblies with increasing polymer concentrations as a function of wave vector q (center) reveal their microstructural evolution. Scale bars are 15 nm. Adapted from ref (29). Licensed under CC BY 4.0. (b) Experimental morphology map of PEC hydrogels as a function of polymer composition and concentration. The symbols denote the following: red circles for disordered (DIS) spheres, blue squares for body-centered cubic (BCC) spheres, green triangles for hexagonally closely packed (HCP) cylinders, orange diamonds for parallelly stacked lamellae (LAM), and pink three-pointed stars for the gyroid (GYR). Adapted with permission from ref (30). Copyright 2020 American Chemical Society. (c and d) Experimental morphology maps of PEC hydrogels as a function of polymer and salt concentrations. In panel d, the disorder–order transition appears at a lower polymer concentration of 12 wt% due to the longer charged block lengths of bPEs. Panel c adapted with permission from ref (12). Copyright 2013 American Chemical Society. Panel d adapted with permission from ref (3). Copyright 2020 American Chemical Society.