Project

Self-assembled double polymer networks: flow and fracture

Double polymer networks consist of two independently cross-linked, water-filled polymer networks that are topologically interlocked. A mechanical synergism between the two networks gives such double network hydrogels an exceptional toughness, which makes them very interesting for usage in biomedical applications.

However, covalently cross-linked double networks have the draw-back that they cannot recover from suffered damage and that, once prepared, the materials are fixed and hard to process. The aim of this project is to develop and study a new class of double polymer network hydrogels, based on physical rather than chemical cross-links.

By choosing associating groups that can be triggered selectively (for example by a change in pH, temperature, or a chemical signal), we obtain dual-responsive materials, with visco-elastic properties that can be tuned from very soft to very stiff. Because the physical bonds can form and break reversibly such physically cross-linked double networks will be self-healing, producing materials that are not only tough, but also smart. These networks will be studied by combining experimental work on mixtures of well characterized triblock copolymers (microscopy, scattering and rheology) with molecular theory and coarse-grained simulations.

Figure 1. (a) Schematic picture of a double polymer network consisting of two interlocked cross-linked networks; (b) mechanism proposed for toughening. Local damage of the first (blue) network softens the material around the crack tip. The energy dissipation of this yielding enhances the fracture energy of the double network and thus increases the resistance to crack propagation.
Figure 1. (a) Schematic picture of a double polymer network consisting of two interlocked cross-linked networks; (b) mechanism proposed for toughening. Local damage of the first (blue) network softens the material around the crack tip. The energy dissipation of this yielding enhances the fracture energy of the double network and thus increases the resistance to crack propagation.