Exploring the effects of nanoparticle incorporation on the mechanical properties of hydrogels.

Recent studies have expanded our understanding of the effects of nanoparticles on hydrogel mechanical properties. However, further studies are needed to validate the generality of the findings, as well as to determine the exact mechanisms behind the enhancements afforded by the incorporation of nanoparticles. In this study, we performed rotational rheological characterizations of chemically crosslinked poly(acrylamide) hydrogels incorporating silica nanoparticles to better understand the role of nanoparticles on the enhanced properties of hydrogel nanocomposites. Our results indicate that the increases in elastic moduli due to the addition of nanoparticles depend strongly on particle size and concentration, as well as the overall concentration of the hydrogel. Moreover, we find that incorporating nanoparticles can lead to enhancements in hydrogel elastic moduli greater than the maxima obtainable through purely chemical crosslinking. Finally, our data indicates a strong role for pseudo-crosslinking mediated by non-covalent interactions between the nanoparticles and hydrogel polymers on the observed reinforcements. Collectively, our results shed further insight into the role of nanoparticles on enhancements of mechanical properties of polymers and may thereby facilitate engineering specific mechanical properties in a wide range of hydrogel nanocomposite systems.