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Nano-hybrid gels : from pure chemical to hybrid networks
Nano-hybrid hydrogels combine a poly(N,N-dimethylacrylamide) covalent network and physical interactions by strong adsorption of polymer chains at the nanoparticle surface. The resulting mechanical behavior of such highly stretchable nano-hybrid hydrogels highlighted a very unusual combination of properties induced by the incorporation of silica nanoparticles : elasticity, dissipation, strength and strain at failure were seen to be enhanced simultaneously. The talk reports on the time-dependence of dissipative mechanisms and probes the characteristic times for self-recovery. A series of model nano-hybrid gels have been designed to obtain well-controlled architecture and formulation. The characteristic times involved in the nanoparticle/polymer associations were investigated by large strain mechanical cycling in a wide range of strain rate. The strong physical interactions taking place between nano-silica particles and PDMA chains were seen to enable the network to rapidly recover its mechanical properties. Total recovery of strain and modulus is typically achieved for time-scales of tens of seconds. The main feature of this work is the remarkable role played by silica nano-particles in the network to promote transient and recoverable connectivity. Such network dynamics opens up interesting prospects for toughening, self-recovering or self-healing applications.