Molecular Mechanics of Polymer Nanocomposites

Polymer nanocomposites have been a central theme in nanotechnology over the last decade. This activity was determined primarily by expectations generated by early experiments showing significant property enhancement associated with the addition of a small fraction of nano-fillers in thermoplastics. A large number of experimental, numerical and theoretical investigations of the physical basis of these enhancements followed. Today it is generally accepted that, while the fillers do not modify chemically the matrix material, the mechanical properties of the polymer are nevertheless altered. This chapter reviews some of the numerical and experimental works aimed at developing this basic understanding. We focus on modifications of the chain structure and relaxation time in the vicinity of impenetrable fillers, the residence time of polymeric chains on filler surfaces in melts, and the formation of a network of chains connecting fillers. This molecular-scale physics has been incorporated in rheological models aimed at predicting the macroscopic response of the composite. One such model is presented here. Despite not reviewing the entire, large literature produced to date on this subject, the discussion provides insight into the essential physics of these systems, and a starting point for future investigations.