| In recent times, nanofillers have attracted the interest of a variety of research groups as these materials can cause unusual mechanical, electrical, optical and thermal enhancements. These enhancements are induced by the presence of the nanoparticles, their interaction with the host matrix, and also quite critically, by their state of dispersion. In this work we find that nanoparticles can be dispersed in linear polymers, despite chemical dissimilarity, when the nanoparticle is smaller than the linear polymer, as demonstrated by the miscibility of polyethylene (PE) nanoparticles in linear polystyrene (PS) or PS nanoparticles in poly (methyl methacrylate) (PMMA) (PS-PE and PS-PMMA are classical phase separating systems). If the particles become larger than the polymer, phase separation occurs with even polystyrene nanoparticles phase separating from linear polystyrene. In addition, small angle neutron scattering shows the linear polymer becomes distorted on the addition of nanoparticles in the stable systems and is far from its equilibrium conformation. This aspect demonstrates the uniqueness of nanoscale thermodynamics as phase separation is expected (i.e. depletion flocculation) and we believe that the nanoparticles are stabilized by enthalpic gain. When properly dispersed, the addition of nanoparticles causes a large reduction (up to 90%) in the melt viscosity of the system, a result at odds with Einstein's century old prediction and experimental observations of the viscosity increase particles provide to liquids (i.e. slurries and suspensions) and melts. Also, the addition of specific nanoparticles, apart from improving the polymer processing by reducing the viscosity, can simultaneously lead to enhanced electrical conductivity (greater than Maxwell's prediction), enhanced mechanical damping (up to 5 fold increase), enhanced thermal stability/fire retardancy, and can even make the polymers magnetic. The above and other unusual nanoscale phenomena are discussed in this work. |
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