Figure 2: Inhomogeneous structure model for the tough DN gels. The first network PAMPS has a mesh size of several nm with large “voids” of size . The second component PAAm chains are in concentrated region and they both are entangled with each other and with the PAMPS network. For clarity, only some of the PAAm chains are highlighted by bolder lines. The voids that are filled with concentrated PAAm act as “crack-stop” to enhance the mechanical strength of the DN gels. Reproduced with permission from [14] © 2003, Elsevier, Inc.