Effect of polymer–particle interaction on the fracture toughness of silica filled hydrogels

We have investigated the mechanical and fracture properties of hybrid hydrogels made of chemically crosslinked polyacrylamide (PAAm) and silica nanoparticles. Unlike the case where the polymer is poly(dimethylacrylamide) (PDMA), the introduction of silica nanoparticles at 6–7 vol% does not lead to any significant reinforcement in the mechanical properties (modulus, hysteresis and fracture toughness) of the hydrogels. The key difference between the two hybrid gels is that PAAm does not absorb on silica while PDMA does L. Petit, L. Bouteiller, A. Brulet, F. Lafuma and D. Hourdet, Langmuir0, 2007, 23(1), 147–158. These results stress the importance of polymer/filler interactions in controlling the macroscopic mechanical properties of hybrid hydrogels and suggest that a strong but breakable interaction leads to superior fracture toughness.