(584d) The Simplicity of Fractal Nanocomposites: Hierarchical Structure and Dynamic Consequences

An outstanding issue in the field of polymer nanocomposite has been to separate and quantify the roles of polymer-particle, particle-particle and polymer mediated particle-particle interactions in controlling properties of such systems. In this study, we have attempted to understand the linear and non-linear rheological properties of the nanocomposites in terms of their structure and the underlying polymer-particle interactions. Neutron scattering studies revealed that, above the percolation threshold, in quiescent state, nanotubes form a hierarchical fractal network made of aggregated flocs or clusters inside which tubes overlap each other to form dense mesh. As a direct consequence of the self-similar fractal network, the linear flow properties display ?time-temperature-composition' superposition. But remarkably, this superposability can be extended for non-linear deformations when the non-linear properties are scaled by the local strain experienced by the elements of the network. More interestingly, under steady shear these nanocomposites show network independent behavior. The absolute stress value is a function of the particle loading but the characteristic time scales related to the process are independent of it. For fully grown particle network in viscous polymer, cluster dynamics under external shear controls the non-linear behavior of the system.