(397al) Effect of Nanoparticles On the Viscoelastic Properties of Poly(acrylamide) Hydrogels

It is well established that the addition of nanoscopic filler particles to polymer systems can have a large impact on mechanical properties, even for very low weight fractions of nanoparticles. However, despite over two decades of research using experimental studies and modeling, the mechanisms behind this reinforcement are still under debate. Our work aims to shed light on the molecular underpinnings of reinforcement in polymer nanocomposites so that specific mechanical properties can be engineered in a wide range of polymer nanocomposite systems. In our current study, we investigated the viscoelastic response of poly(acrylamide) hydrogels containing silica nanoparticles of various sizes and concentrations. The polymer density and crosslink density of the hydrogels were controlled by manipulating the relative concentrations of acrylamide monomer and N,N-methylenebis(acrylamide) crosslinker. Initial results suggest that the elastic modulus of the hydrogels depends strongly on particle size and concentration. In addition, the relative increase in the elastic modulus of the nanocomposite compared to the pure polymer appears to depend strongly on the overall concentration of the gel. Furthermore, we find that incorporating nanoparticles can result in gel stiffnesses greater than the maximum that is obtainable through purely chemical crosslinking. Future work will explore the fundamental nature of this reinforcement.